Issuu

Geological Society of Australia

ABSTRACTS Number

Victorian Universities Earth Sciences Conference A Meeting Organised by the Students of:

Monash University School of Geosclences 5 September 2003

VU ESC The

Victorian Universities Earth Sciences Conference

MONASH U N I V E R S I T Y

A Meeting Organised by the Students of the School of Geosciences at l\/lonash University 5 September 2003

Geological Society of Australia Abstract Volume Number 70

Geological Society of Australia

Abstracts Number 70

17th Victorian Universities Earth Sciences Conference Abstracts Volume Editors' Names:

Rene D. LaBerge Virginia G. Toy

ISSN 0729-011X

Geological Society of Australia Incorporated, 2003

Citation for this volume: LaBerge, R.D. and Toy, V.G. (Editors),2003, 2003, Victorian Universities Sciences Conference, September Geological Society of AustraliaEarth Abstracts 70, 65 p.

Example of citations for papers in this volume: Author, A.B., 2003, Title of paper, In: R.D. LaBerge and V.G. Toy (Editors), Victorian Universities Earth Sciences Conference, September 2003, Geological Society of Australia Abstracts 70, p. 5. OR Author, A.B., 2003, Title of paper. Geological Society of Australia Abstracts

Copies of this publication

may be obtained from:

The Business Manager Geological Society of Australia Incorporated Suite 706 Thakral House, 301 George Street Sydney NSW 2000 Australia

70, p. 5.

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

Programme 9:00-9:15

^ . „ . Opening Remarks:

9:15-10:15 9:15-9:30 9:30-9:45

Jim Cull - School of Geosciences, Monash University ' Peter Pritchard - Geological Society of Australia, Victoria Division

Session 1: Geochemistry, Geomorphology, and Volcanology Can the Late Miocene Ramadas Volcanic Centre of NW Argentina's Andean Puna be Classified as a Collapse Caldera?

M.A. TAIT, R.A.F. Cas, andJ.G. Viramonte

The Use of Electron Microprobe Analysis to Determine the Distribution of Mid-Holocene Tephras in Central New Britain

T. HASSELL, P. Jackson, and J. Webb

9:45-10:00

Geomorphology, Chronology and Late Cainozoic Environments of Greens Swamp, Upper 1 Wimmera Catchment Victoria M.J. HOCKING

10:00-10:15

The Geology and Geomorphology of the Zahrat Adh-Dhra' Region, Dead Sea Plain, Jordan

10:15-10:30 10:30-11:15 10:30-10:45 10:45-11:00 11 00

E. HOUSE, J. Webb, and P. Edwards

Break for Morning Tea Session 2: Palaeontology and Sedimentology Diagenesis of the Nullawarre Greensand, a Late Cretaceous Ooidal Ironstone Fades in Southeastern Australia G.A. BOYD Cambrian Sediments in the Songshan Range, Henan Province, China and their Archaeological Significance

j.j.

GORTON, J.A. Webb, G. Xu, andL Liu

11-15 ' Oligocene Cetacea (Mammalia) from the Southern Margin of Australia E.M.G. FITZGERALD

11:15-11:30

Break

11:30-12:30

Session 3: Climatology and Hydrogeology

11:30-11:45

A Possible Reversal of the Leeuwin Current During the Cenozoic as Shown by New Zealand and SE Australian Corals M. GROVER

11:45-12:00

Assessment of Extratropical Cyclones in the CSIRO Coupled GCM with Increasing CO2

12:00-12:15

Temperature Trends in the Mallee Wimmera Wheat Belt and Some Implications

12:15-12:30 12:30-1:30 1:30-2:30 1:30-1:45 1:45-2:00

E.-P. LIM and 1. Simmonds A. LAING

Simulating Snow Depths at Australian Alpine Locations LA. CORBET, 1. Smith, and 1. Simmonds

Lunch: MUGS Barbecue Session 4: Structural Geology and Tectonics Evolution into the Stagnant Lid Regime with an Ice Rheology J. FREEMAN, L. Moresi, and D. May

Laminar Shear Flow and Composite Fabric Development in the Rauer Group, East Antarctica C. QUINN, D. Kelsey, and C.J.L. Wilson

2:00-2:15

The Structural Evolution of the Gum Creek Field Area, Olary Domain, South Australia

2:15-2:30

Evidence for a Core Complex in Central-East Queensland

2:30 - 2:45 2:45 - 3:45

K. FRY and P Betts D.G. WOOD and G.S. Lister

Break for Afternoon Tea Session 5: Economic Geology and Environmental Studies

2:45 - 3:00

Structure and Alteration of Basaltic Ocean Crust, Caroline Cove, Macquarie Island

3:00-3:15

The Volcano-Sedimentary and Structural Architecture of the Wildwood Prospect, Western Lachlan Orogen: A Comparison with the Stawell Gold Deposit

S.J. LEWIS and G.J. Davidson

A.L KAUFMAN

3:15-3:30 3:30 - 3:45 4:00 - 5:30

Structural Controls on Central Lode Mineralisation within the Magdala Gold Mine, Stawell, 1 Western Victoria J.A. ROBINSON The Composition and Stability of Mine Drainage Treatment Sludges J. WOOLLARDandJ.A.

Poster Session

5:30 - 5:45

Judges Deliberation

5:45-6:15

Awards and Closing Remarks

6:30

Conference Dinner

Webb

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

The Committee of the 1 Victorian Universities Earth Sciences Conference would like to thank the following sponsors for their kind support:

MONASH U N I V E R S I T Y

Monash University School of Geosciences

Geological Society of Australia

DeB E E R S A

DIAMOND

FOREVER

De Beers Exploration

PIACER DOME AS^ PACIFIC Placer Dome Incorporated

Geological Society of Australia Abstracts 70

17'" Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

Australian Institute of Geoscientists

The Australian Institute of Mining and Metallurgy

The Australian Society of Exploration Geophysicists

Commonwealth Scientific and Industrial Research Organisation

Esso Australia Pty. Ltd. iv

Geological Society of Australia Abstracts 70

17'" Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

Geological Society of Australia - Victorian Division

Geological Sun/ey of Victoria

"Sinking i n d u s t r y a n d students"

Geoscience Victoria Student Industry Organisation

MINERALS COUNCIL OF AUSTRALIA

Minerals Tertiary Education Council (MTEC)

MONASH U N I V E R S I T Y

Monash University School of Geosciences Postgraduate Student Organisation

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

Petroleum Exploration Society of Australia Ltd.

pmd^RC Predictive Mineral Discovery Cooperative Research Centre

THE U N I V E R S I T Y OF

MELBOURNE

The University of Melbourne - School of Earth Sciences

Victorian Institute of Earth and Planetary Sciences

V ict o r ia n ^^ 1 n e

•Mkf &

a is

e n e r g y

council

Victorian Minerals and Energy Council VI

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

Contents SESSION ONE: GEOCHEMISTRY, GEOMORPHOLOGY, and VOLCANOLOGY Can the Late Miocene Ramadas Volcanic Centre of NW Argentina's Andean Puna be Classified as a Collapse Caldera? M.A. TAIT, R.A.F. Cas, andJ.G.

Viramonte

The Use of Electron Microprobe Analysis to Determine the Distribution of Mid-Holocene Tephras in Central New Britain T. HASSELL, P. Jackson, and J. Webb

Geomorphology, Chronology and Late Cainozoic Environments of Greens Swamp, Upper Wimmera Catchment Victoria M.J. HOCKING

The Geology and Geomorphology of the Zahrat Adh-Dhra' Region, Dead Sea Plain, Jordan E. HOUSE, J. Webb, and P. Edwards

Fluctuating Magmatic and Phreatomagmatic Eruptions at the Quaternary Red Rock Volcanic Centre, Southeastern Australia A.R CHEESMAN, and R.A.F. Cas

A Combined U-Pb and LA-ICPMS Hf-lsotope Study of Zircon from S-Type Granites and Associated Enclaves, Lachlan Fold Belt, SE Australia R. KEMP, J. Hergt, J. Woodhead, and I. Williams

Substrate Deformation Produced by the Shear Force of a Pyroclastic Density Current: An Example from the Cimino Ignimbrite, Northern Lazio, Italy R.D. LABERGE, G. Giordano, and R.A.F. Cas

Rockfall Hazard Asssessment of the Bluff, Barwon Heads, Victoria B.J. MULLER

Varied Basaltic Eruption Styles of the Mount Leura Volcanic Complex within the Newer Volcanics Province of Southeastern Australia A. SHAW-STUART

and R.A.F. Cas

Development of a Fissure-Vent System toward a Shield Volcano - An Example Within, and Implications For, the Newer Volcanics Province, Victoria, Australia R. TROWBRIDGE and R.A.F. Cas

SESSION TWO: PALAEONTOLOGY and SEDIMENTOLOGY Diagenesis of the Nullawarre Greensand, a Late Cretaceous Ooidal Ironstone Fades in Southeastern Australia G.A. BOYD

Cambrian Sediments in the Songshan Range, Henan Province, China, and their Archaeological Significance J.T GORTON, J.A. Webb, G. Xu, andL. Liu

Oligocene Cetacea (Mammalia) from the Southern Margin of Australia E.M.G. FITZGERALD

Oligocene-Recent Canyon Systems of the Otway Basin, Victoria, Australia /A.S. LEACH and M.W. Wallace

Mammalian Biochronology of Australia - An Early Pleistocene Assemblage from Nelson Bay, Portland, Victoria K.J. PIPER

The Paraphyly of Nambaroo (Marsupialia: Macropodoidea) and its Biostratigraphic Implications L.R.S. SCHWARTZ

Observations on the Early Cretaceous Palynoflora and their Palaeoclimatic Implication D.E. SEEGETS-VILLIERS

VII

Geological Society of Australia Abstracts 70

17*^ Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

SESSION THREE: CLIMATOLOGY and HYDROGEOLOGY A Possible Reversal of the Leeuwin Current During the Cenozoic as Shown by New Zealand and SE Australian Corals M. GROVER

Assessment of Extratropical Cyclones in the CSIRO Coupled GCM with Increasing CO2 E.'P. LIM and I. Simmonds

Temperature Trends in the Mallee Wimmera Wheat Belt and some Implications LAING

Simulating Snow Depths at Australian Alpine Locations LA. CORBET, I. Smith, and I. Simmonds

Hydrogeology and Water Chemistry of the Campaspe Irrigation Area C. TANAKA andJ.A. Webb

The Origin of Salinity in the Hopkins River J.L WATTIEandJ.A.

Webb

SESSION FOUR: STRUCTURAL GEOLOGY and TECTONICS Evolution into the Stagnant Lid Regime with an Ice Rheology 33

J. FREEMAN, L Moresi, and D. May

Laminar Shear Flow and Composite Fabric Development in the Rauer Group, East Antarctica C. QUINN, D. Kelsey, andC.J.L

Wilson

The Structural Evolution of the Gum Creek Field Area, Olary Domain, South Australia K. FRY and P. Betts

Evidence for a Core Complex in Central-East Queensland D.G. WOOD and G.S. Lister

Evolution of the South African Drakensberg High-Elevation Passive Margin: New Insights from Low Temperature Thermochronologic Data from Deep Boreholes V.-A. DIMASandR.W.

Brown

Strain Partitioning and a Detachment in the Broken Hill Block, NSW 33

C.J. FORBES, andP.G. Betts

The Structural Evolution of the Dead Horse Synform, Olary Domain, South Australia 39

C. LORINI and P. Betts

Three Dimensional Slab Structure of the Northwest Pacific Margin M.S. MILLER

Quantifying the Role of Normal Fault Growth, Segmentation and Interaction on Sedimentation During Ancient Basin Formation: A Case Study from the Late Cambrian Owen Conglomerate, West Coast Range, Western Tasmania C.A. NOLL andM. Hall

Formation of Arcuate Orogenic Belts in the Western Mediterranean Region 42

G. ROSENBAUM and G.S. Lister

Structural Evolution of the Minerva Anticline, Otway Basin, Southeast Australia - Inversion During Regional Extension 43

C.L SCHNEIDER, K.C. Hill, and N. Hoffman

A Revised Model for Convergence Between India and Asia 44

V.G. TOY, G.S. Lister, and C. Duboz

VIII

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

SESSION FIVE: ECONOMIC GEOLOGY and ENVIRONMENTAL STUDIES Structure and Alteration of Basaltic Ocean Crust, Caroline Cove, Macquarie Island S.J. LEWIS and G.J. Davidson

The Volcano-Sedimentary and Structural Architecture of the Wildwood Prospect, Western Lachlan Orogen: A Comparison with the Stawell Gold Deposit A.L KAUFMAN

Structural Controls on Central Lode Mineralisation within the Magdala Gold Mine, Stawell, Western Victoria 49

J.A. ROBINSON

The Composition and Stability of Mine Drainage Treatment Sludges J. WOOLLARD and J.A. Webb

A Rock-Magnetic Study of Bacterially Mediated Iron Sulfide Diagenesis Associated with Gas Hydrate-Bearing Sediments J.A. HOLLAMBY and R.J. Musgrave

Regolith Mapping at Bendigo, Central Victoria, Australia A. KOTSONIS, B. Joyce, and S. Carey

The Lake Boga Granite, Northwest Victoria —Uranium in Fluorapatite and its Implications for Secondary Mineralisation 53

S.J. MILLS

The Geology, Age, Near Surface Features, and Mineralogy of the Merlin Kimberlite Field, Northern Territory, Australia W.R.H. RAMSAY, A. Hell, G. Reinberger, and S. Pooley

A Laboratory Study of the Conditions Governing Iron Precipitation within Anoxic Limestone Drains S. SANTOMARTINO and J.A. Webb

Geochemistry and Architecture of the NiS Deposit, Riwaka Complex, Graham Valley, West Nelson, New Zealand R. SMITS, S.W. Beresford, and B. Schaefer.

Phosphorous Fixation in Acid Sulphate Soils of the Coode Island Silt, Central Victoria D.T.VU, J. Webb, and P. Sale

The 440 Ma Mineralising Event in the Lachlan Fold Belt: Result of a Tectonic Mode Switch? I.M.A. VOS, G.S. Lister, and F.P. Bierlein

Structural and Metallogenic Characteristics of Gold Deposits in the Amanda Bel Goldfield, Broken River Province, NE Queensland, Australia 59

I.M.A. VOS, F.P. Bierlein, and G.S. Teale

Fertility of the Agnew Komatiite, Agnew, Western Australia H.M. WALLACE, S. Beresford, and R.A.F. Cas

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

2003 VUESC Organising Committee Conference Convenor:

; Caroline Forbes

Abstract Volume Editors:

: Rene LaBerge 1 Virginia Toy Mark Tait

Website Design:

1 Nic Rosengren j Abstract/Web Coordinator:

Pattie Sie

: Sponsorship:

Christian Noll Ivo Vos Anthony Morey

Publicity:

Leah Schwartz Ana Storey John Clulow

Catering:

Katrina Fry Ben Petrides

Audiovisual:

Trevor Allen Jill Middleton

; Poster Session: Conference Dinner:

David Wood GeoViSIO David Wood

General Support:

Rob Duncan i Melissa Gregory : Yusen Ley-Cooper Adrian Pittari

Session Convenors: 51) Adrian Pittari and Olivier Reubi 52) Christian Noll and Leah Schwartz 53) Andrew Marshall® and Elisabetta Carrara"^ 54) Quinton Hills^ and Craig Schneider"^ 55) Robert Duncan and Silvana Santomartino'" ^ Australian Crustal Research Centre ® Bureau of Meteorology, Monash University ^ La Trobe University ^ The University of Melbourne

Thanks also to:

nuns 2003

Monash University Geological Society

Geological Society of Australia Abstracts 70

17'" Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

SESSION ONE GEOCHEMISTRY, GEOMORPHOLOGY, and VOLCANOLOGY

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

CAN THE LATE MIOCENE RAMADAS VOLCANIC CENTRE OF NW ARGENTINA'S ANDEAN PUNA BE CLASSIFIED AS A COLLAPSE CALDERA? M,A. T A I T \ R.A,F. C a s \ a n d J.G, Viramonte^ ^ School of Geosciences, Monash University, PO Box 28E Melbourne Australia, 3800 ^ Institutio Geonorte, Universidad Nacional de Salta, Buenos Aires 177, Salta, Argentina The Altiplano-PUna Volcanic Zone of South Americas Central Andes is world famous for its high density of collapse caldera structures. The Ramadas Volcanic Centre (RVC) is located within this region and lies -3800 m a.S.I. in NW Argentina's Salta Province. The RVC is identified as the source for the distinctive rhyolitic Corte Blanco Tuff (CBT), which is dominated by coarse widespread pumiceous fallout deposited from a sustained plinian eruption column. The RVC is geo-morphologically defined by a 4 x 5km "amphitheatre", set within hills of uplifted Precambrian basement. Presently, thick Quaternary fanglomerates cover much of the local landscape, largely obscuring the RVC and its associated deposits. Where exposed, facies within the vent comprise a thick arcuate sequence of pyroclastic surge deposits, coarse lithic breccias, limited fallout deposits and a lava dome. A negative gravimetric response has been identified across the proposed vent. This is consistent with significant removal of country rock, and filling of the vent with juvenile material during the eruption. According to recent workers, this is also indicative of caldera collapse, and the term "cryptic" caldera has been used to describe the largely obscured RVC.

Re-assessment of the dominant facies types of the CBT, and modelling of the local gravimetric response indicates that it is unlikely that piston style subsidence occurred during eruption of the RVC. The morphology of the vent, the modelled subsurface structure of the complex and the sustained nature of the eruption column are consistent with pulsating but minimal variations to the magma discharge rate and inconsistent with catastrophic collapse of the chamber roof during the eruption. Using current models for the mechanisms of caldera formation, the RVC is best described as a "funnel" caldera, similar in morphology to numerous young Japanese calderas (eg. Nigorakawa). However, the scale and style of the RVC eruption can more simply be explained as a highly explosive vent with an associated diatreme sourcing a deep magma chamber. As there is no evidence for significant collapse during this eruption, it seems unreasonable to classify the RVC as a collapse caldera. Furthermore, this work questions the classification of explosive systems as "funnel" calderas, particularly as many systems are categorised based solely on geophysical response, and interpreted sub-surface geometry, often with little evidence for significant or catastrophic collapse within the vent or its conduit.

Keywords: Andes, Collapse Caldera, Ramadas, Plinian tait@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

THE USE OF ELECTRON MICROPROBE ANALYSIS TO DETERMINE THE DISTRIBUTION OF MID-HOLOCENE TEPHRAS IN CENTRAL NEW BRITAIN T. HASSELL, P. Jackson, and J. Webb Department of Earth Science, LaTrobe University, Victoria 3086, Australia Central New Britain is an area of active volcanism. Through the mid Holocene there were several large scale eruptions of Witori volcano, 20km south east of Hoskins. In particular two such eruptions occurred at 5600 BP and 3300 BP, known as W-K1 and W-K2 respectively. These volcanic events had a dramatic effect on the landscape and human population occupying central New Britain at the time. An ash deposit of 50cm is sufficient to devastate rainforest vegetation and make an area uninhabitable for several years. W-K2 ash forms deposits up to 40cm thick at sites approximately 100km from the Witori volcano. The material deposited would have been enough to kill rainforest vegetation, pollute streams and damage animal and human life. Because of this, archaeologists are interested in establishing the tephrostratigraphy resulting from volcanic activity in central New Britain. Volcanic ash samples were taken from archaeological excavation sites on the north, central and southern parts of central New Britain, and analyses were performed

on pristine glass fragments extracted from the tephras. Electron microprobe analysis showed that glasses from separate eruptions are readily distinguished by plotting Fe (expressed as FeO) against CaO. Weathered samples are easily recognised by the loss of CaO relative to FeO and can be eliminated from the data sets. In this way tephra samples can be attributed to an individual eruption event. Previous studies have shown that the W-K1 and W-K2 tephras are distributed across the northern part of central New Britain, but further sampling and analysis has revealed that the dispersal of volcanic material from these eruptions extends 150km to the south coast where significant deposits have been recorded. Thus, without considering ash fall to the north or east of Witori volcano, each of the W-K1 and W-K2 eruptions covered an area of at least 10 000 km^ with an average thickness of 10-40cm of ash. The spread of material is comparable to the massive eruption of Taupo, New Zealand in 186 AD.

Keywords: New Britain, tephra, volcanic glass, tephrostratigraphy, archaeology. tmhassell@yahoo.com.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

GEOMORPHOLOGY, CHRONOLOGY AND LATE CAINOZOIC ENVIRONMENTS OF GREENS SWAMP, UPPER WIMMERA CATCHMENT VICTORIA MJ. HOCKING Department of Physical Science & Engineering, La Trobe University, Bendigo, Victoria 3550 Australia Various analytical techniques including OSL and C^^ dating have been used to determine the geomorphologic evolution of Greens Creek Catchment, a tributary of the Wimmera River 20 kilometres north east of Stawell. The focus of the study is a wetland complex, including the lower reaches of the catchment near the Wimmera River and Heifer Station Creek confluence. The catchment is characterised by Palaeozoic sedimentary rises, kaolinised in the lower parts of the landscape with two source-bordering clayrich dunes fringing the wetland. The development of clay dunes at the foothills of Palaeozoic geology is unique to Greens Swamp within the Upper Wimmera, and is rare throughout the Murray Basin. The initiation of Greens Swamp began prior to 35,000 BP during the development of stream levees associated with the Shepparton Formation. During this time, an extensive levee of Shepparton Formation developed, effectively damming Greens Creek catchment. Since then surface water export from the catchment has been restricted. From around 26,000 to 20,000 BP stream flows gradually decreased as the glacial maximum was approached. The glacial maximum was cold, windy and relatively dry; as a consequence vegetation growth was poor. Low rainfall during this period minimised overflow and ensured surface water did not export from the catchment. Assisted by levee damming, a swampland therefore

Keywords: geomorphology, lunette, Upper Wimmera mark@hockingetal.com

developed in the lower parts of the catchment. Waterlogging as a result of poor drainage and low vegetation growth rates increased groundwater levels that became saline over time. As the catchment has a westerly aspect and is extremely flat in the lower reaches, the summer dominant westerly winds ensured water remained on the eastern side of the swamp. A complex of conditions including extensive areas of unvegetated, waterlogged, saline soil of poor structure allowed the initiation of a lunette on the eastern side of the swamp around 25,500 BP +/- 1,300. Once initiated a period of rapid dune development occurred over the next 2-5 thousand years, followed by an abrupt end to the lunette building phase. Although the period at and after the last glacial maxima was favourable for extensive lunette formation across southern Australia, no record of these episodes is preserved in the Greens Creek catchment. A second, smaller clay dune to the west of the main lunette was initiated at 5,330 BP +/- 160. This dune appears to be intermittently active with material currently being added to the crest and flank. Organic sediment dated around 1,390 BP +/- 70, accumulated up-catchment of the older lunette, is inferred to represent a wetter climate. This concurs with a documented La Nina phase in Australia.

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

THE GEOLOGY AND GEOMORPHOLOGY OF THE ZAHRAT ADH-DHRA' REGION, DEAD SEA PLAIN, JORDAN E. HOUSE\ J. Webb\ and P. Edwards' ^ Department of Earth Sciences, La Trobe University, Victoria, Australia ^ Department of Archaeology, La Trobe University, Victoria, Australia Situated on the south eastern edge of the Dead Sea in Jordan, the Zahrat adh-Dhra' region lies on the hyperarid Dead Sea Plain, and is bordered by the Lisan Peninsula to the west and the Jordan Valley margin to the east. Geological investigation of this region was undertaken as part of the 'Archaeology and Environment of the Dead Sea Plain' project, a study which aims to expand on current knowledge of the cultural and natural history of the Dead Sea Plain. Present within the Zahrat adh-Dhra' area are two archaeological sites: a PrePottery Neolithic A (PPNA) settlement dated to 9,500 yrs BP (ZAD 2) and 200m to the south, a Middle Bronze Age (ca. 2,000-1,500 BC) village (ZAD 1). Detailed geological mapping of a 10km^ area identified three major formations. The oldest is the Eocene Um Rijam Chert-Limestone Formation (URC) a dominantly foraminifera-rich limestone containing lensoidal beds of chert. Generally steeply dipping to the west, the URC lies on the western section of the Dhra' Monocline, an arc-like flexure splaying off the Dead Sea Fault and present along the eastern margin of the mapped area. Conformably overlying the URC are a series of Oligocene-Miocene sandstones, marls, calcarenites and poorly sorted chert conglomerates belonging to the Dana Formation. Extensive faulting of these beds has produced variously tilted blocks, some of which are capped by the well-lithified chert conglomerate beds to form resistant ridges. In turn the Dana Formation is unconformably overlain by the horizontally bedded Pleistocene Lisan Formation. (60,000-13,000 yrs BP). Consisting of poorly consolidated gravel beds, sands and laminated marls these

deposits accumulated in and adjacent to Lake Lisan, the precursor to the Dead Sea. The contact between the base of the Pleistocene Lisan Formation and the top of the Oligocene-Miocene Dana Formation is sharp, the gravels of the Lisan Formation mantling the pre-existing topography. A contour map delineating the base of the Lisan Formation reveals that the prePleistocene topography was characterised by a valley and ridge morphology. This morphology resulted from faulting of the Dana Formation to produce tilted blocks and is significantly different to the mostly flat plains that characterise this part of the landscape today. Influence over the distribution of facies within the Lisan Formation is attributed to this valley and ridge morphology, with the occurrence of laminated marls restricted to pre-existing depressions. Much of Zahrat adh-Dhra' is a flat plain dipping gently towards the west, the northern half of which has been badly dissected by deep gullies (wadis). Both the archaeological sites of ZAD 1 and 2 are located on flat-topped ridges between wadis and have undergone erosion as a result of incision by Wadi adh-Dhra', which is fed by a permanent spring and follows the strike of a NW-SE trending fault. A comparison of Dead Sea level fluctuations with the timing of erosion through the archaeological sites of ZAD 1 and 2, suggests that base level changes were not responsible for wadi incision. Instead, the occurrence of Wadi adh-Dhra' in the vicinity of a major fault combined with evidence of significant surface displacement either side of Wadi adh-Dhra' points towards tectonically induced incision.

Keywords: Dead Sea Plain, Zahrat adh-Dhra', Dana Formation, Lisan Formation topography, geomorphology, archaeology. Pleistocene. emilyr_house@yahoo.com.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

FLUCTUATING MAGMATIC AND PHREATOMAGMATIC ERUPTIONS AT THE QUATERNARY RED ROCK VOLCANIC CENTRE, SOUTHEASTERN AUSTRALIA A.R CHEESMAN, and R.A.F. Cas School of Geosciences, Monash University, PO Box 28E Melbourne Australia, 3800 The Red Rock Volcanic Centre is a nested complex of maars and scoria cones comprising over 40 identifiable vents. Volcanism was entirely explosive with eruption styles varying from Strombolian to Hawaiian to phreatomagmatic. The centre is located in close proximity to other explosive centres in the Western Plains subprovince of the Pliocene-Pleistocene Newer Volcanics Province of Victoria and South Australia. Magmatic eruptions were dominantly Strombolian producing highly vesicular scoriaceous lapilli. A limited period of Hawaiian volcanism occurred throughout the centre forming deposits of agglutinated spatter. Phreatomagmatic eruptions resulted from the interaction between ascending magma and groundwater within underlying Tertiary aquifers. Grainsize variation of the pyroclasts from ash to lapilli represents changing efficiency in the water-magma explosive interaction as both magma ascent and aquifer recharge rates fluctuated.

Stratigraphic relationships show two main stages of volcanism: an early phreatomagmatic stage as magma interacted with the groundwater, and a late stage magmatic phase. Phreatomagmatic pyroclasts including abundant accessory sediments from the subsurface aquifers were deposited by base surges with minor pyroclastic fallout. Sedimentary structures reflecting surge emplacement include pervasive low angle cross-stratification, undulatory strata, and scour and fill. Minor interbedded scoria represents temporary Strombolian pulses when the magma ascent exceeded aquifer recharge and the conduit became water depleted. Scoria was the major product of the late stage magmatic eruptions and was deposited by fallout processes in proximal localities. Magmatic eruptions were facilitated by the depletion of water from the local aquifer system. Interbedded ash facies intervals mark a temporary reversion to phreatomagmatic eruptions as water re-entered the conduit.

Keywords: pyroclastic, phreatomagmatic, Strombolian, base surge, maar, scoria cone cheesy@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

A COMBINED U-Pb AND LA-ICPMS Hf-ISOTOPE STUDY OF ZIRCON FROM S-TYPE GRANITES AND ASSOCIATED ENCLAVES, LACHLAN FOLD BELT, SE AUSTRALIA R. KEMP\ J. Hergt\ J. Woodhead\ and 1. Williams^ ^ School of Earth Sciences, The University of Melbourne, Victoria, 3010, Australia. ^ Research School of Earth Sciences, The Australian National University, Canberra, 0200, Australia.

It is widely acknowledged that the preservation in granites of older grains of the mineral zircon provides unambiguous (albeit small) direct samples of components that have materially contributed to the magma. Identification of so-called inherited grains is based on the determination of their U-Pb ages, made possible by in situ analysis using the Sensitive High Resolution Ion Microprobe (SHRIMP). SHRIMP analyses of zircons from the Lachlan Fold Belt granites have revealed distinctive inheritance patterns. The age distributions in the inherited zircons from batholithic S-type granites show very similar patterns to those preserved in the Ordovician sediments into which the granites have been emplaced. Virtually every S-type zircon has an inherited core and these are dominantly - 5 0 0 - 6 0 0 Ma, with a secondary peak at 1,000-1,200 Ma, and less abundant older grains of up to 3500 Ma. Similar analyses performed on mafic enclaves have suggested that the abundance and age populations of inherited zircon grains are very similar to those in the host granite, providing a petrogenetic link between the two. The preservation of similar inheritance patterns in examples of both S- and l-type

Lachlan Fold Belt magmas is used by the proponents of mixing models to indicate that essentially all granites in the Lachlan Fold Belt of SE Australia contain a c o m m o n sedimentary component from the continental crust. Thus, it can be argued that there is a continuum in granite compositions, with variable contributions from a limited number of components, resulting in the observed variations in bulkrock chemistry. Despite the advances offered by S H R I M P U-Pb analyses in providing the means of unravelling age information preserved in single zircon grains extracted from granites, nevertheless, the debate surrounding granite petrogenesis remains because these ages do not identify directly the source(s) of the elements that grew the zircon grains. A question that arises as a c o n s e q u e n c e is how the ages of the inherited zircons relate to the sources of these grains (e.g., indisputably the same source material or alternatively a different source of the same age)? In situ isotope analyses of zircons extracted from the Jillamatong Granite and its mafic enclaves have been conducted, and provide an unparalleled opportunity to test existing models of granite petrogenesis.

Keywords: SHRIMP, U-Pb, Hf-lsotopes, LA-ICPMS, S-type Granites, Jillamatong rdkemp@ozemail.com.au

Geological Society of Australia Abstracts 70

17* Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

SUBSTRATE DEFORMATION PRODUCED BY THE SHEAR FORCE OF A PYROCLASTIC DENSITY CURRENT: AN EXAMPLE FROM THE CIMINO IGNIMBRITE, NORTHERN LAZIO, ITALY R.D. L A B E R G E \ G, G i o r d a n o ^ a n d R.A.F. Cas^ ^ School of Geosciences, P.O. Box 28E, Monash University, Clayton, VIC 3800 Australia ^ Dipartimento di Scienze Geologiche, Universita Degli Studi Roma Tre, Largo S. Leonardo Murialdo n 1 00146 Roma, Italy Several small reverse faults offset the basal contact of the Cimino ignimbrite near the town of Vitorchiano,

northern

Lazio,

Italy. At this location, the ignimbrite consists of about 15 m of welded fades above 1.5 m of non-welded base. The middle Pleistocene ignimbrite overlies poorly consolidated silt and clay of Pliocene to early Pleistocene age. The exposed faults displace the basal contact of the ignimbrite up to 65 cm, and extend down into the clay another 30 cm, where they sole into a complex fracture zone resembling a decollement. Although they are not lithified, the sediments appear to have behaved in a brittle manner, producing striations on polished fault surfaces. In contrast, faults within the non-welded base of the ignimbrite dissipate within one to two metres of the contact. Over this short distance, faults change from planar surfaces to intergranular offsets, which cannot be traced.

This suggests that faulting occurred before the base of the ignimbrite was consolidated, and possibly before the upper part of the ignimbrite was deposited. There is no apparent offset of the welded facies by these faults, which supports the idea that faulting occurred prior to welding. These faults are situated at the top of the slope along the edge of a northeasttrending palaeo-valley. Sole marks and imbrication in the ignimbrite suggest that the pyroclastic density current flowed parallel to the axis of this palaeo-valley. Striations on fault surfaces indicate that motion on the faults was parallel to the pyroclastic flow direction. These data support the interpretation that the faults were produced by the shear force of the pyroclastic density current on the substrate, as it flowed down the palaeovalley, during deposition of the ignimbrite, prior to compaction and welding.

Keywords: Cimino, ignimbrite, Italy, palaeotopography, Pleistocene, pyroclastic density current, substrate deformation, volcanism rene@earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

ROCKFALL HAZARD ASSSESSMENT OF THE BLUFF, BARWON HEADS, VICTORIA BJ. MULLER Geology Department, University of Ballarat, Victoria 3350 Australia Engineering geological investigations have been conducted at The Bluff, Barwon Heads, to aid in the understanding of the hazards associated with rockfall events. It is envisaged that the research undertaken in this one-year Honours degree will assist the Barwon Coast Committee of Management in their responsibility to ensure safe beach access to this popular tourist destination, as well as contribute to the more regional issues of coastal slope stability. The Bluff represents a lee side section of the Pleistocene coastal dune system, classified as the Bridgewater Formation, that geographically spans large sections of the south coast of Victoria. The Bridgewater Formation consists of a thick sequence of aeolian calcarenite, interspersed with calcretized palaeosol horizons that formed during cessations in dune building and associated stabilisation and vegetation development. The rockfall hazard assessment applies both traditional deterministic methods and the integration of more current probabilistic approaches to the investigation and analysis of the site. Initially a detailed geologic and geomorphic assessment was undertaken. Subaerial denudation was found to be the

predominant slope forming process with variations in slope morphology dependant on the presence of calcrete capping protecting lower units from gullying and incision. Eight modes of rockfall failure have been identified and can be categorised broadly into overhang failures, falls from lower sections of overhangs, dipslip failures or by toppling moments. Spatial variation of the differing rockfall types is defined by the orientation of bedding in relation to the slope face, and the development or presence of overhangs. Rock strength parameters for deterministic analysis were determined by mechanical laboratory testing of the various rock types in relation to their modes of failure. Values obtained from the testing provide the parameters for the appropriate limiting equilibrium equations to determine Factors of Safety for the Bluff. Analysis of the large historic photo collection revealed that there have been significant changes to the Bluff, indicating an active state of subaerial denudation and mass wasting over the past 100 years. A brief inspection of the influence of rockfall triggering events will also be conducted as part of this study.

Keywords: rockfall hazards, coastal geomorphology, deterministic analysis, probabilistic analysis Briony_Muller@ekit.com

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

VARIED BASALTIC ERUPTION STYLES OF THE MOUNT LEURA VOLCANIC COMPLEX WITHIN THE NEWER VOLCANICS PROVINCE OF SOUTHEASTERN AUSTRALIA A, SHAW-STUART and R.A.F. Cas School of Geosciences, Department of Earth Science, Monash University, Victoria, Australia The Mount Leura Volcanic Complex (MLVC) is situated within the most recent basaltic province of Australia, the Newer Volcanics Province (NVP). The NVP is a continental intraplate basaltic province that features large plains lavas punctuated by scoria cones, maars, tuff rings and cones. NVP literature suggests that the plains lavas are generally tholeiitic and erupted before the later stage alkalic cones and tuff rings. The NVP spans the northern margin of the Otway Basin, and overlies overriding the Palaeozoic basement of the Lachlan Fold Belt (LFB). Its east-west orientation is thought to reflect the influence of basement faults associated with the formation of the Otway Basin during rifting between Australia and Antarctica. Underlying the MLVC, effusive tholeiitic magma has not interacted explosively with water during the ascent. A later stage alkalic magma batch erupted phreatomagmatically producing a large tricentric tuff ring hosting multiple scoria cones of decreasing size. The MLVC stratigraphic sequence consists of basal tuff, overlain with scoria that contains intercalated lava. Phreatomagmatic eruptions occurred during interaction between rising alkalic magma and water saturated carbonate sediments of the

Otway Group during the Tertiary. The deposits are characterised by depositional structures formed under high flow regimes. Structures vary from low angle crossstratified beds, through dune bedding, to highly truncated angular trough cross-sets. Magmatic deposits of the MLVC vary from scoria, through blocks and bombs facies and agglutinate and clastogenic lava. The scoria deposits are reverse to normally graded and reflect variation of the eruption dynamics. Reverse size grading reflects increasing column height, eruption intensity, and dispersal, whereas normal size grading reflects the opposite, and/or incipient transgression into hydrovolcanic eruptions. The tuff ring formed by a combination of transportation processes: surges, fallout and surge-modified fall deposits. Magmatic deposits are formed as a result of diminishing interaction between water and magma - either the consequence of aquifer exhaustion or the formation of a magma seal preventing interaction. The MLVC represents a downsequence of eruption intensity from initial phreatomagmatic activity, through strombolian scoria cone building, to effusive lava eruptions producing clastogenic lavas and agglutinate deposits.

Keywords: phreatomagmatic, base surge, tuff ring, tri-centric, basalt, scoria, clastogenic, agglutinate. Newer Volanics Province shaw@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

DEVELOPMENT OF A FISSURE-VENT SYSTEM TOWARD A SHIELD VOLCANO - AN EXAMPLE WITHIN, AND IMPLICATIONS FOR, THE NEWER VOLCANICS PROVINCE, VICTORIA, AUSTRALIA R. TROWBRIDGE and R.A.F. Cas School of Geosciences, Monash University, Clayton, VIC 3168, Australia The Quaternary Mt Eccles Volcanic Complex (MEVC) is located in the southwest of the basaltic intraplate Newer Volcanics Province (NVP) of Victoria, Australia. The complex comprises aligned cones, a spectacular fissure vent system and an extensive lava field, including a single flow extending approximately 50km to the sea. The lava field dominates the MEVC, and the cones complex is only a small percentage of the total erupted volume. The main eruptive styles that characterized the complex were Hawaiian fire-fountaining and lava effusion, with minor Strombolian explosive eruption, and phreatomagmatism. These styles were not uniform in the complex - often eruptive styles varied between cones and within stratigraphy. Variations in eruptive styles were largely due to non-uniform conduit widths, magma-water interaction, and variable magma and gas flux. The presence of lava tubes, channels and tumuli in a digitate fan-shaped flow field indicates sustained high-effusion eruptive activity. The change from older, longer, tube-fed flows to younger, shorter, channelised flows reflects a transition in eruptive style from sustained, relatively longer duration, high effusion rates to pulsating yet high effusion rates. The morphological change of the flow field may reflect progressive evolution of the storage of magma ponded in the crust, such as storage position, or changes in internal plumbing. Geochemical analysis reveals a range of basaltic rocks, with a strong Ocean Island Basalt character, indicating a broadly similar melting regime. The geochemical signatures of the MEVC are consistent with the geochemical signatures of the NVP transitional plains basalts.

however the MEVC is unusual in that it is geochemically complex, including hawaiites, nepheline hawaiites, basanites and alkali olivine basalts. There appears to be no evolution in the MEVC from tholeiitic to alkalic magma, and geochemical types are not limited to particular constructional features, as has been proposed for the NVP. There is, however, a strong suggestion of mixing between two end-member sources resulting in the range of MEVC rocks. Some geochemical types are spatially separate, and petrographic evidence such as skeletal olivine and aphyric appearance of the MEVC rocks indicate rapid ascent from separate deep level magma chambers. The morphology of the MEVC is similar to Icelandic volcanoes, which developed through successive stages beginning with an initial fissure eruption concentrating at certain points, forming a central vent and erupted lavas. Major lava tube systems are developed after months to years, and cones are limited in size as most of the erupted volume is delivered to the flow field. Cone development occurs over decades, after which a high shield is formed with lava-coated tumuli, and larger rootless outflow complexes on the flanks. The fact that there is an extensive tube network in the MEVC, with a voluminous lava flow-field, low edifices, indicates the MEVC was in the intermediate stage of shield volcano evolution. The complexity of the MEVC suggests further detailed studies of small-volume complexes within the NVP are required, to further shed light on the dynamics of magma generation, evolution and migration in this intraplate province.

Keywords: Mt Eccles, Newer Volcanics Province, flow field, geochemistry, fissure, shield. bek@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

17'" Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

SESSION TWO PALAEONTOLOGY and SEDIMENTOLOGY

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

DIAGENESIS OF THE NULLAWARRE GREENSAND, A LATE CRETACEOUS OOIDAL IRONSTONE FACIES IN SOUTHEASTERN AUSTRALIA G.A, BOYD School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia. The Late Cretaceous Nullawarre Greensand of the Sherbrook Group, Otway Basin, is dominated by a marine ooidal ironstone facies. The colour of Nullawarre Greensand is usually attributed to the presence of glauconite. However, investigation has revealed that within the Port Campbell Embayment the green clay mineral berthierine is a more dominant pigment than glauconite. The berthierine is present as a thin coating over quartz grains. Further petrological studies, scanning electron microscope analysis, and microprobe results have revealed an unusual mineralogy and texture in the Nullawarre Greensand that includes the

presence of berthierine ooids, glauconite pellets, siderite and phosphate cements, pyrite, and the rare-earth-element (REE) phosphate mineral rhabdophane. Together, these grains, cements, and minerals provide strong evidence that the Nullawarre Greensand was deposited in a shallow to near coastal marine environment with a relatively high energy, during a period of reduced clastic sediment influx. The unusual mineralogy of the Nullawarre Greensand has given insight into the unit's environment of deposition and in turn has given new perspective on the depositional history of the Sherbrook Group.

Keywords: Nullawarre Greensand, ooidal ironstone, mineralogy, berthierine. g.boyd2@pgrad.unimelb.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

CAMBRIAN SEDIMENTS IN THE SONGSHAN RANGE, HENAN PROVINCE, CHINA AND THEIR ARCHAEOLOGICAL SIGNIFICANCE J . T . G O R T O N \ J . A . W e b b \ G. X u \ a n d L

Liu'

^ Department of Earth Sciences, La Trobe University, VIC, Australia ^ Department of Archaeology, La Trobe University, VIC, Australia Hui Zui, adjacent to the Songshan Range of Henan Province in Central China, is believed to be one of the key locations for mass stone tool manufacturing during the Late Neolithic and Bronze ages. Tools at the site are dominated by spades made from limestone and dolostone, most likely derived from the Cambrian sediments outcropping in the Songshan Range, a few kilometres South of the site. The geology of a 25km^ area in the Songshan Range was mapped at a scale of 1:10,000, to determine likely source units from which the raw material for the spades was derived. This survey was conducted in coordination with a La Trobe archaeology team directed by Dr. Li Liu as part of the Yellow River Project Survey. A 2-D geological map and associated 3-D digital terrain model show which units outcrop on the North side of the range, and which is most accessible for the gathering and transport of raw material in large amounts for mass stone tool production. The Lower Cambrian deposits in the Songshan Range consist of conglomerates and quartzitic sandstones with increasing carbonate cement. Up section, these sediments grade upwards into Middle Cambrian red shale with interbedded carbonates, overlain by Upper Cambrian Carbonates. Detailed stratigraphic sections within the thick-bedded carbonates of the Middle and Upper Cambrian revealed cyclic sequences with a variety of characteristics indicative of a shallow marine carbonate platform. These include rip-up clasts, ooids, peloids,

oncolites, burrows, stromatolites, ripple cross-stratification, and hummocky crossstratification. The dominant rock type is oolitic with ooid size varying from very small (0.1-0.4 mm in diameter), to quite large (0.8-1.2 mm in diameter), with the latter most often occurring in association with argillaceous banding. Ooid nuclei include calcite crystals, micrite clasts, and fossil fragments; ooids are mostly spherical while fabrics are dominantly radial. In some beds, large concentrations of highly elongate ooid grains have been observed coating trilobite skeletal fragments. Fossils are dominated by many varieties of trilobites, echinoderms and stromatolites, but also include significant amounts of bivalves and cephalopods. Thin section and cathode ray luminescence analysis has identified multiple cementation phases and dissolution of ooids, as well as partial and complete dolomitisation. The first cement phase is fibrous marine, followed by coarse sparry burial cement. Dissolution of ooids, forming oomoulds, has occurred mostly after the precipitation of burial cement. Ooid dissolution is often nonuniform, with oomoulds and ooids occurring together. Partial dolomotisation is observed as small dolomite rhombs replacing fine-grained ooid cortices and micrite patches while coarser-grained cement is unaffected. Other beds show a more complete dolomitisation, exemplified by a continuous dolomite mosaic with relict structure of ooids and fossils in various states of preservation.

Keywords: Archaeology, Neolithic, spades, Songshan, Cambrian, limestone, dolostone, ooids, dissolution, oomoulds jgorton@students.latrobe.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

OLIGOCENE CETACEA (MAMMALIA) FROM THE SOUTHERN MARGIN OF AUSTRALIA E.M.G. FITZGERALD School of Geosciences, P.O. Box 28E, Monash University, Victoria 3800 Australia Museum Victoria, P.O. Box 666E, Melbourne, Victoria 3001 Australia Australia has a hitherto unrecognised diversity of Oligocene Cetacea (whales, dolphins and porpoises). Baleen-bearing whales (suborder Mysticeti), toothed echolocating whales (suborder Odontoceti), and the primitive archaeocetes (suborder Archaeoceti), are represented by fossils from Oligocene deposits of southern Australia. The majority of these fossil cetaceans were derived from the Late Oligocene Jan Juc Formation, Torquay Basin, central coastal Victoria. These sediments were deposited in mid-shelf settings on the margin of Bass Strait. Although many of these fossils are fragmentary, they indicate the presence of a wide range of taxa, morphology and inferred palaeoecology. Mammalodon colliveri is a small, aberrant, whale displaying a mosaic of primitive and derived features. Preliminary phylogenetic analyses posit this species as perhaps the most primitive known member of the Mysticeti. Several undescribed specimens probably represent new species of Mammalodon. Isolated and partially complete remains from the lower Jan Juc Formation, near Torquay, represent probable delphinoid and platanistoid odontocetes, archaic mysticetes, and

possible basilosaurid archaeocetes. The sole published record of a cetacean from the Early Oligocene of South Australia, "Squalodon" gambierensis, may be a basilosaurid archaeocete. The Oligocene was a critical epoch in cetacean evolution, with the odontocetes and mysticetes undergoing an extensive adaptive radiation at this time. It has traditionally been thought that the transition from archaeocete-dominated faunas, to mysticete and odontocetedominated faunas, occurred abruptly at the Eocene-Oligocene boundary. Oligocene cetacean faunas from the southwest Pacific appear to be quite different to those of the North Pacific. Australia and New Zealand have yielded Early and Late Oligocene cetacean faunas that include basilosaurid archaeocetes, as well as more derived cetaceans. The coexistence of three suborders of Cetacea during the Oligocene suggests that cetacean evolution, and partitioning of resources, was more complex than previously thought. Further research is needed to determine the evolutionary patterns and processes of Australian Oligocene Cetacea, and their relationships with North Pacific Oligocene Cetacea.

Keywords: Australia, Oligocene, Cetacea, Pacific, Mysticeti, Odontoceti, Archaeoceti, evolution erichmgf@mail.earth.monash.edu.au efitzger@museum.vic.gov.au

Geological Society of Australia Abstracts 70

M^^ Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

OLIGOCENE-RECENT CANYON SYSTEMS OF THE OTWAY BASIN, VICTORIA, AUSTRALIA A.S. LEACH and M.W. Wallace School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia. Australia's southeastern margin is host to a diverse range of both ancient and modern submarine canyon systems. Preserved within the Otway Basin's Tertiary cool-water carbonates, several of these canyons have been imaged using bathymetric and seismic data. Two morphologically distinct submarine canyon systems can be recognised: 1) OligoceneMiocene canyon systems, and 2) PlioceneRecent canyon systems. The Oligocene-Miocene canyons are mainly found on the eastern side of the offshore Otway Basin within the Heytesbury Group. These submarine canyons consist of either simple isolated cut and fill canyons, or stacked canyon systems. The smaller cut and fill canyons are characterised by a simple history of erosion followed by canyon filling. The later, are long-lived complex systems that migrate laterally towards the west. Within each system, the canyons are also stacked vertically, with the younger canyons above and to the west of the older underlying canyons. The fill within both canyon types also progrades towards the west. The fill within the Oligocene-Miocene canyon at Thylacine#1 is mainly made up of coarse-grained packstones. The basal fill of these canyons is characterised by a high calcite content (up to 80%) and high sonic velocities. This manifests as velocity 'pull-ups' on seismic sections. The oldest Oligocene-Miocene canyons initiated on the slope, near the base of the Heytesbury Group, above the Clifton Formation. This suggests canyon growth began during the Late Oligocene to Early Miocene and continued through to the Late Miocene. Canyon activation was therefore within the basal Gellibrand marl, which

appears to represent a major transgression (in onshore strata). This transgression may have been a major controlling factor of canyon formation. The Pliocene-Recent canyons are generally found to the west and seaward of the Miocene canyons. These canyons are preserved within the dominantly Pliocene Whalers Bluff Formation. The fill within Pliocene-Recent canyons is generally symmetric or eastward orientated. The oldest Pliocene canyons can be distinguished on total magnetic intensity images, suggesting the canyons have a magnetic and probably clastic component to their fill. Directly seaward of the Pliocene canyons, Recent canyons incise the modern slope. The positions of the major modern canyons coincide with the larger Pliocene canyons. This suggests that they are essentially extensions of the older Pliocene canyons. As shelf progradation occurred, the canyons on the slope migrated seaward. The change from westward orientated fill in the Oligocene-Miocene to eastward orientated fill in the Pliocene is likely to be a result of major oceanic changes in the region. This canyon fill orientation suggests that during the Miocene there was a strong west-directed current on the slope. At approximately the MiocenePliocene boundary a weak east-directed current was established. The change in canyon position is also likely to be a result of uplift at the MioPliocene boundary. The uplift event and widespread erosion would have produced a greatly increased sediment supply offshore, re-activating canyon formation at this time.

Keywords: submarine canyons, seismic, Otway Basin, Heytesbury Group, Whalers Bluff Formation, Oligocene-Miocene, Pliocene-Recent. a.leach1@pgrad.unimelb.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

MAMMALIAN BIOCHRONOLOGY OF AUSTRALIA - AN EARLY PLEISTOCENE ASSEMBLAGE FROM NELSON BAY, PORTLAND, VICTORIA K J , PIPER School of Geosciences, Monash University, Victoria 3800, Australia The Plio-Pleistocene mammalian fossil record is most complete in southeastern Australia, however the Early Pleistocene is still very poorly represented. Nelson Bay is a 6 km wide crescent shaped bay situated 5 km SW of Portland, and approximately 320 km WSW of Melbourne, Victoria (141° 35' E., 38° 36' S.). The Nelson Bay Formation, from which the Nelson Bay Local Fauna has been collected, outcrops in steep cliffs and is composed of a repeating series of calcarenites and calcareous clays and sands. It has been interpreted as a series of freshwater lacustrine or lagoonal sediments, and has been dated to between 1.77-0.78 million years old. This is one of the few terrestrial mammal sites where biostratigraphic data from marine invertebrates (foraminifera) and terrestrial vertebrates can be combined with good palaeomagnetic and radiometric data to obtain a precise age. It is the only well

dated diverse Early Pleistocene site in Australia, and as such is an important calibration point. At least 30 taxa are present in the assemblage, making it an extremely diverse fauna. Many of the species are yet to be identified and are potentially new. The fauna is dominated by the Macropodidae (kangaroos), but also contains several carnivores, large herbivores ('diprotodontoids'), and less abundant remains of possums, rodents, a koala, wombat and echidna. It is particularly interesting as it contains modern taxa, members of the megafauna, and relict taxa from the Early Pliocene. The Nelson Bay Local fauna has the potential to reveal valuable information about species diversity in the Early Pleistocene, how marsupials adapted to the changing climate, and fills an important gap in Australian terrestrial mammal biochronology.

Keywords: Early Pleistocene, Portland, Victoria, mammals, biochronology. kpiper@mail.earth.monash.edu

Geological Society of Australia Abstracts 70

1 / Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

THE PARAPHYLY OF NAMBAROO (MARSUPIALIA: MACROPODOIDEA) AND ITS BIOSTRATIGRAPHIC IMPLICATIONS LR.S. SCHWARTZ School of Geosciences, Monash University, Victoria 3800, Australia The description of Nambaroo bullockensis, from Bullock Creek in the Northern Territory has extended the range of this plesiomorphic (primitive) genus from the Late Oligocene into the middle Miocene. This species is the largest known for the genus, and displays a mosaic of both primitive and derived features. Cladistic analysis of the kangaroo subfamily Balbarinae shows that the genus

Nambaroo is in fact paraphyletic, and suggests that as many as three different monophyletic genera could be created from the current concept of Nambaroo. This has important biostratigraphic implications for Australian Tertiary Mammal sites where the utility of macropodoids in marsupial biochronological schemes has just begun to be recognised.

Keywords: Macropodoidea, Balbarinae, Bullock Creek, Nambaroo, marsupial biochronology leah@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

OBSERVATIONS ON THE EARLY CRETACEOUS PALYNOFLORA AND THEIR PALAEOCLIMATIC IMPLICATION D.E. SEEGETS-VILLIERS School of Geosciences, Monash University, Victoria 3800, Australia The Early Cretaceous Flat Rock Fossil Site (Gippsland, Victoria) has long been known for its diverse vertebrate fossil content. Intriguing about the site are not only the biota preserved but also the fact that it was located well within the Antarctic Circle during the time of deposition. According to recent findings this geographic position let to a MAAT (mean annual air temperature) of between -2°C and +3°C. Low temperatures such as these raise questions about what animals and plants would have survived such harsh conditions. The faunal component has been, and still is being, studied extensively. The floral component has, however, so far only played a subordinate role as a dating tool. Samples were, therefore, taken from the site and their palynological assemblage investigated. Findings were then compared to those from two other Early Cretaceous sites (Koonwarra and Kilcunda) also within the Gippsland Basin in order to establish similarities and differences in the floral makeup and to see if climatic implications could be discerned. The ongoing study has so far revealed some interesting results. The Flat Rock samples are low in diversity but rich in

number of individual grains. These samples reflect a dominance of fern species, with subordinate presence of gymnosperms. The Koonwarra Site, where the climate had previously been established as having been cool, exhibits an overall higher diversity, a generally much lower fern count but a greater presence of gymnosperms. The Kilcunda Cliff Site shows a yet higher diversity, but much lower number in individual grains. Fern counts are mainly high, with often equal or higher gymnosperm counts. Provided that the proposed temperature range is correct and that the floral assemblage does not represent a local microenvironment, then the following suggestions can be made: The Kilcunda and Koonwarra Sites were subjected to a more tolerable, yet still cold climate. This is supported by the higher diversity of taxa. Some gymnosperm taxa, which occurred consistently at these sites, but not at Flat Rocks were possibly less tolerant of the colder conditions. The dominance of ferns at Flat Rocks indicates their excellent adaptation to the hostile conditions proposed for this site.

Keywords: Early Cretaceous, palynoflora, palaeoclimate doris@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

Geological Society of Australia Abstracts 70

1Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

SESSION THREE CLIMATOLOGY and HYDROGEOLOGY

Geological Society of Australia Abstracts 70

M^^ Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

A POSSIBLE REVERSAL OF THE LEEUWIN CURRENT DURING THE CENOZOIC AS SHOWN BY NEW ZEALAND AND SE AUSTRALIAN CORALS M. GROVER Deakln University, Melbourne Campus, 221 Burwood Highway, Burwood, VIC 3125 Australia It is now understood that one of the fundamental aspects of coral biogeography is that even though ocean currents drive dispersion, widely separated localities with similar physical environments have a greater affinity than those having adjacent locations. For example, in the modern context, corals of the north-west shelf of Australia have a greater similarity to those of the Great Barrier Reef than they have with adjacent mainland coasts. This same aspect can be seen between the Cenozoic corals of New Zealand and southeastern Australia. One possible mechanism to allow this similarity in fauna is the possibility of a reversal of the Leeuwin Current. There has been some discussion on this reversal during the Pliocene but was this reversal longer lasting, or did it occur more than once? There appears to be evidence that certain coral genera and species evolved

in New Zealand and were then transported to southeastern Australia. For example, both Sphenocyathus (Acinocyathus) springer and Flabellum (Pavonium) distinctum, first appeared in the Bortonian (Middle Eocene) in New Zealand, and then appeared in the Janjukian (Oligo-Miocene) at Torquay. On a generic scale, Oculina first appears in the lower Miocene of New Zealand, and then doesn't appear until the Cheltenhamian (Pliocene) of southeastern Australia. Trochocyathus appears in the Bortonian (mid-Eocene), before being present in southeastern Australia during the Oligo-Miocene, and Notocyathus first appears in the Duntroonian (Lower Oligocene) of New Zealand, before showing up in the Janjukian of southeastern Australia. The reversal of the current flow between Australia and New Zealand would explain this inconsistency.

Keywords: current reversal, Cenozoic, scleractinian corals grover@deakin.edu.au

Geological Society of Australia Abstracts 70

M^^ Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

ASSESSMENT OF EXTRATROPICAL CYCLONES IN THE CSIRO COUPLED GCM WITH INCREASING CO2 E.-P. LIM and I. Simmonds School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia Extratropical cyclones comprise daily weather pattern in the mid and high latitudes where the most human population is distributed. Also, they maintain the atmospheric budgets of energy, momentum and moisture by redistributing them across the globe. Due to their crucial roles in human life and atmosphere balance, it is important to understand the future behaviour of these synoptic systems in the warmer world. This study is aimed to examine any changes in cyclone frequency, intensity, scale and depth caused by increasing CO2 in the extratropical regions of the globe. To do this, we use the data from the control, transient IxCOz and SxCOz runs of the CSIRO MARK2 atmosphere-ocean

coupled model. The Melbourne University cyclone finding and tracking scheme is used to identify low-pressure systems. According to our analysis, it is found that there is a general reduction in cyclone frequency at mean sea level as the CO2 level increases. Cyclone scale tends to get greater in the 2xC02 simulation. On the other hand, the changes in the intensity and depth of cyclones are found differently depending on regions. With tripled CO2 the frequency of cyclones shows a further decrease. The physical features of them tend to also experience slight decreases, which implies a certain process of stabilisation from 2xC02 to 3XC02.

Keywords: extratropical cyclone, carbon dioxide, general circulation model eplim@earthsci.unimelb.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

TEMPERATURE TRENDS IN THE MALLEE WIMMERA WHEAT BELT AND SOME IMPLICATIONS A. LAING School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia The growth of wheat at seven sites in the Mallee Wimmera region is investigated. Spring wheat growth is quantified using simple rainfall and temperature criteria to identify the beginning and length of the growing season. Historical variability of

the growing season in the Mallee Wimmera wheat belt is examined and possible future trends identified. Implications of the effects of changing temperature trends on the growing season of wheat are discussed.

Keywords: wheat, climate change alisonml@earthsci.unimelb.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

SIMULATING SNOW DEPTHS AT AUSTRALIAN ALPINE LOCATIONS L A . C0RBET\ 1. Smith^ and 1. Simmonds^ ^ School of Earth Sciences, The University of Melbourne, Victoria 3800 Australia ^ Division of Atmospheric Research, CSIRO, Aspendale, Victoria 3195 Australia The ski industry in Australia is vulnerable to poor snow cover with many Australian alpine locations already relying on manmade snow to enhance the quality of their resort's snow cover. Studies in Australia and overseas expect snow cover durations and depths to decrease under enhanced greenhouse conditions. An empirical snow model is being created to simulate snow depth with daily

temperature and precipitation data. The model calculates snowfall and ablation from the data to arrive at each day's snow depth. Daily calculations of snow depth are expected to be more accurate than interpolated monthly calculations, which have previously been used to investigate Australian snow cover under a climate of enhanced greenhouse conditions.

Keywords: snow, depth, snowpack, simulation, daily, model l.corbet@ugrad.unimelb.edu.au

Geological Society of Australia Abstracts 70

1 / Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

HYDROGEOLOGY AND WATER CHEMISTRY OF THE CAMPASPE IRRIGATION AREA C. TANAKA and J.A. Webb Department of Earth Sciences, La Trobe University, Vic. The Campaspe Irrigation Area is a very active agricultural region. In recent years, a decline of ground water quality has been reported in the area, correlated with significant increases ground water extraction. The primary aim of this project is to examine the relationship between groundwater usage and the water quality decline. There are two aquifers in the area, the Shepparton Formation with high salinity ground water, and the underlying Deep Lead, with fresh ground water, which is pumped extensively for agricultural usage. The Shepparton Formation consists of clays with some sand, while the Deep Lead, which consists of two major units, Calivil Formation and the underlying Renmark Group, comprises largely sand and gravel. The Shepparton Formation is relatively impermeable than the Deep Lead, and its vertical hydraulic conductivity is extremely low. However it has been proposed that increased pumping of the Deep Lead ground water has resulted in seepage from the overlying aquifer, and raised the salinity of the ground water of the Deep Lead. A full understanding of the hydraulic interaction between the two aquifers is urgently required. In terms of the hydrogeology of the area, two approaches have been used to constraint water leakage between the two aquifers: the groundwater composition,

and chronological change of salinity and potentiometric surface of the two aquifers. Several bores from the Deep Lead show marked rises in salinity and decline of the potentiometric surface over the last 10 years. On the other hand, a gradual salinity decrease and relatively stable water table was observed in the Shepparton Formation. This is probably due to the recharge of fresh irrigation water diluting the salt concentration and maintaining the water level. The decline in potentiometric surface of the Deep Lead is probably due to the ground water extraction increasing the hydraulic gradient between the two aquifers, leading to increased seepage flow from the overlying saline ground water, and raising salinity in the Deep Lead. The existing hydrogeological model of the area predicted the volume of seepage from the upper aquifer to the Deep Lead. This was checked using a mass balance calculation, given that the shallow ground water is approximately three times more saline than the Deep Lead water, and the predicted seepage value was shown to be too large, considering to the salinity in the Deep Lead aquifer. The greater understanding of the hydrogeological system in the area will be significant for future decision making of ground water allocation in the area.

Keywords: Campaspe Irrigation Area, salinity, hydrogeological system chihiro102@hotmail.com

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

THE ORIGIN OF SALINITY IN THE HOPKINS RIVER J . L WATTIE and J.A. Webb School of Earth Sciences, La Trobe University, Victoria, Australia Over the last few decades, the Hopkins River has become more saline. This is problematic as it threatens both the native flora and fauna in and around the river. The Hopkins River is situated in Western Victoria, rising just north of Ararat and flowing south to the sea at Warrnambool. There are three main tributaries that run into the river: Mt Emu Creek, Brucknell Creek, and Salt (also known as Fiery) Creek. Mt Emu Creek and Brucknell Creek have catchments with a higher average precipitation than the Hopkins River, so the water entering the Hopkins River at these two tributaries markedly increases the flow of the river and decreases the salinity level. This project sampled 45 sites along the river (and tributaries) twice in the current year, summer (March) and winter (July), of these sites, 30 had a full chemical analysis. In addition, there is comparative data from the 1990s. At the headwaters of the Hopkins River, downstream to just south of Ararat, the salinity in the river fluctuates, but is fairly low (an average of 5mS/cm). The major region of salinity input starts north of Willaura and extends for approximately 45

km to just south of Wickliffe. The salinity in the river increases to approximately 15 - 20mS/cm, due to input from groundwater flow from salt lakes in this region, in particular. Lake Buninjon. Further downstream, the salinity drops steadily until the intrusion of the sea at the mouth of the river. This drop in salinity can be largely attributed to inflow from the tributaries already mentioned (Mt Emu Creek and Brucknell Creek), and the general increase in flow of the river. The salinity also varies according to the flow of the river, decreasing as the flow increases. The salinity drops approximately 6mS/cm with an increase of flow of 5ML/Day. This variability was also highlighted by the summer 2003 measurements during the current drought, when the salinity was the highest recorded and the flow was minimal, accentuating the amount of evaporation in almost stagnant pools in the river, and probably also allowing greater than normal intrusion of saline groundwater from the salt lakes into the river. From this study, it is hoped that ways of reducing the inflow of salinity may be identified and implemented.

Keywords: salinity, salt lakes, evaporation bungkecil@yahoo.com

Geological Society of Australia Abstracts 70

17'" Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

SESSION FOUR STRUCTURAL GEOLOGY and TECTONICS

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

EVOLUTION INTO THE STAGNANT LID REGIME WITH AN ICE RHEOLOGY J. FREEMAN' ^ L. Moresi' ' ^ and D. M a y ' ^School of Mathematical Sciences, Monash University, Victoria 3800, Australia ^School of Geosciences, Monash University, Victoria 3800, Australia ^Monash Cluster Computing, Monash University, Victoria 3800, Australia Victorian Partnership for Advanced Computing, Carlton South, Victoria 3053, Australia Numerical investigations of thermal convection with strongly temperature dependent Newtonian viscosity (diffusion creep) and extremely large viscosity contrasts have demonstrated the existence of three convective regimes. These are the small viscosity contrast regime, transitional regime and the stagnant lid regime. The strong temperature dependence of water ice suggests that convection operating within the mantle of an icy satellite should be within the stagnant lid regime. We study the evolution into the stagnant lid regime with a water ice rheology by solving the equations of thermal convection for a creeping fluid with the Boussinesq approximation and infinite Prandtl number. The viscosity is non-Newtonian (dislocation creep). We fix the Rayleigh

number at the base (Ra^) to be 1x10"^ and systematically increase the viscosity contrast (as determined by AT) over the region from Ar| = 1 to The transition to the stagnant lid regime occurs at a viscosity contrast greater than 10^ for Newtonian viscosity convection, whilst non-Newtonian viscosity convection accommodates the stagnant lid regime at larger viscosity contrasts. For a stress exponent, n, equal to 3, the stagnant lid regime is achieved at a viscosity contrast greater than 10^ Dislocation creep of water ice is characterized by a larger stress dependence (A?=4) than silicates (a7=3), and with this water ice rheology, the stagnant lid regime is attained at a viscosity contrast greater than 10^°.

Keywords: Thermal convection, non-Newtonian viscosity, water ice rheology, icy satellite justin.freeman@sci.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

LAMINAR SHEAR FLOW AND COMPOSITE FABRIC DEVELOPMENT IN THE RAUER GROUP, EAST ANTARCTICA C. QUINN, D, Kelsey, and C J . L Wilson School of Earth Sciences, The University of Melbourne, Parkville, 3010 The Rauer Group, situated on the eastern margin of Prydz Bay, east Antarctica, records a complex sequence of overprinting shear zones that developed at a very high-temperature (>950 degrees C). Within each shear zone, a gneissic fabric encloses attenuated mafic fragments, isolated fold hinges and mafic schlieren to form a composite fabric parallel to the shear zone margin. Definition of laminar fluid flow greatly simplifies tectonic interpretation. The theoretical construction in terms of observable quantities (shear strain) follows:

Let be angular rotation. Define shear strain (y) such that y = tan observe that as [\) approaches 90 degrees, tan approaches When applied to any mineral fabric; if y approaches at a point X, then a fabric element s is tangent to the velocity v at x. Consequently, if y approaches for all x then the set S of all s, is the tangent space of the set V of all v. The fabric now provides flow lines from this point, structural interpretation becomes a fluid mechanical problem. By defining laminar flow in this way a number of critical corollaries can be drawn regarding the orientation and timing of deformation.

Keywords: Shear strain, composite fabric, Rauer Group, Antarctica, fluid-flow c.quinn@pgrad.unimelb.edu.au

Geological Society of Australia Abstracts 70

1 / Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

THE STRUCTURAL EVOLUTION OF THE GUM CREEK FIELD AREA, OLARY DOMAIN, SOUTH AUSTRALIA K. FRY and P, Betts School of Geosciences, Australian Crustal Research Centre, Monash University, Victoria 3800, Australia The tectonic evolution of the Olary Domain is characterised by poly-deformation and metamorphic events that record two orogenic cycles. The first cycle occurred during the Palaeo- to Mesoproterozoic Olarian Orogeny. The second cycle occurred during the Cambrian Delamerian Orogeny. The earliest deformation recognised in the Olary Domain is characterised by high temperature shear zones and a penetrative layer parallel fabric. D1 high temperature shear zones are defined by migmatite horizons within the lower half of the stratigraphy (Wiperaminga Subgroup), indicating that high temperature metamorphism and melting coincided with D1 shearing. The second generation of deformation to be preserved in the Olary Domain formed during lateral translations of crustal rocks during nappe-tectonics. D2 is characterised by isoclinal recumbent folds and second generation high temperature shear zones. The non-cylindrical nature of D2 isoclinal folds is responsible for the varied fold interference patterns identified between D2 and D3 structures. Microscopic analysis has shown that D2 folds preserve axial planar mineral growth (biotite), indicating high-temperature metamorphism. Overprinting D2 folds are

east-west trending, upright to inclined, open to tight third generation folds. The fold interference patterns encountered between D3 and D2 are a combination of type 2 and type 3 fold interference patterns. This is due to the non-cylindrical nature of D2 folds. Microscopic analysis of D3 folds has shown that there is minor axial planar mineral growth associated with this generation of folding. D3 folds are defined by stylolites and/or crenulations, indicating that D3 occurred during retrograde metamorphic conditions. The fourth generation of deformation marks a distinct change in the intensity and orientation of deformation in the Olary Domain. D4 is characterised by northsouth trending, open folds. A spaced fracture cleavage has been identified as the S4 axial planar cleavage. Type 1 to type 2 fold interference patterns have been identified between D3 and D4 folds, resulting in doubly plunging D3 folds. The final phase of deformation to be preserved is characterised by retrograde east-west trending shear zones. Dip slip movement is commonly observed in these shear zones, however there has also been significant dextral strike slip movement, with 3-4 km displacement observed.

Keywords: Olary Domain, Olarian Orogeny, folds, shear zones, poly-deformation kmfry@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

EVIDENCE FOR A CORE COMPLEX IN CENTRAL-EAST QUEENSLAND D.G. WOOD^ and G.S. Lister^ ^Australian Crustal Research Centre, School of Geosciences, Monash University, VIC 3800, Australia ^Research School of Earth Sciences, The Australian National University, ACT 0200, Australia Metamorphic core complexes are enigmatic features of continental crust that form in response to extreme crustal extension. They are divided into an upper plate (hanging wall) and lower plate (footwall) separated by a detachment fault. The lower plate consists of ductiley deformed strata that is exhumed along the detachment and exposed at the surface in a domal culmination. The upper surface of the lower plate is mylonitised, and often brecciated adjacent to the detachment. The upper plate is characterized by brittle stretching, reflected as listric normal fault arrays that sole into the detachment. Stretching of the lithosphere associated with detachment causes asthenospheric upwelling. Crustal melts that accompany this upwelling are emplaced as plutons and may enhance the domal culmination in which the metamorphic core complex is exposed. Bimodal magmatism may also accompany pluton emplacement. Exposure and doming of the lower plate surface results in rapid erosion, and sediments which are deposited unconformably as coarse detritus on the lower flanks of the rising dome and adjacent listric fault blocks. Metamorphic core complexes have been recognised in the North American

Cordillera, The Greek Islands, New Zealand, the Norwegian Caledonides and other parts of the eastern European Alps. Locally a metamorphic core complex has been recognized in the northern New England Orogen of eastern Australia. It has been interpreted as forming during the Permo-Carboniferous switch from active accretion to extension along the eastern margin of Gondwana. We provide field evidence that indicates the presence of a previously unrecognized metamorphic core complex in central-east Queensland. Comprising the Anakie Inlier, this feature is located approximately 600km inland of the core complex already identified in the northern New England Orogen, and probably formed at a similar time. New structural data from key localities have highlighted detachment faults, mylonites and unconformity relationships consistent with evolution of a metamorphic core complex. This is contrary to previous interpretations that the Anakie Inlier formed from emplacement as a thrust sheet or nappe. The exhumation of the Anakie Inlier is directly linked to the formation of the Drummond and Bowen Basins, providing a new model for the evolution of these economically important structures.

Keywords: metamorphic core complex, Anakie Inlier, Drummond Basin, Bowen Basin, detachment fault, extension, tectonics dwood@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

EVOLUTION OF THE SOUTH AFRICAN DRAKENSBERG HIGH-ELEVATION PASSIVE MARGIN: NEW INSIGHTS FROM LOW TEMPERATURE THERMOCHRONOLOGIC DATA FROM DEEP BOREHOLES V.-A. DIMAS and R.W. Brown School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia Research into the continental break-up process and passive margin evolution has been largely restricted to studies of topography and sediment delivery to offshore basins up until recently. Advanced applications of low temperature thermochronology have provided new insights into denudation and the erosional behaviour of passive margins. Apatite fission track analysis (AFTA) coupled together with (U-Th)/He analysis is a powerful technique in this regard, as they provide information on palaeotemperatures ranging from -60° - -110° +/-10° C (Apatite Fission Track Analysis) and - 3 5 ° -75° C (U-Th)/He Analysis. The major escarpment forming the Drakensberg, or "Dragon Mountain", is South Africa's most prominent geomorphic feature located on the eastern border with Lesotho. This is a typical high-elevation passive margin and has been the subject of several studies including the use of AFTA and cosmogenic isotopes to better understand its formation and destruction. These studies have estimated a minimum of 4.5 km of denudation having occurred since formation of the margin -130 Myr ago for the coastal zone. Deep boreholes provide a window into greater depths of the continental crust and they are true vertical profiles, with all samples

sharing the same geographic coordinates (except for depth). Apatite Fission Track data from two deep boreholes, Ladybrand (LA 1/68) and Swartberg (SW 1/67) have recorded a major cooling event in the mid-late Cretaceous -90-100 Ma. These two boreholes form a transect along the Drakensberg. New AFT data from the Weltevrede (WE 1/66) and Sprinfontein (SP 1/69) boreholes confirm this cooling event. These two boreholes also form a transect across the passive margin. Maximum palaeotemperatures of surface rocks are likely to be in the range 50° - 60° C hence indicating - 5 0 ° of cooling (accounting for a surface temperature of 10° C). Apatite (U-Th)/He analysis has refined previous AFT palaeotemperature estimates from a deep borehole slightly further inland of the escarpment plateau, Colesberg (CB1). As with the other boreholes analysed, the data from CB-1 indicates a cooling of - 5 0 ° C at 90+/-10 Ma implying denudation of - 2 km during the mid-Cretaceous. Patterns of denudation suggest that he Drakensberg Escarpment formed by rapid post-breakup river incision seaward of a pre-existing drainage divide located east of the present escarpment location. It subsequently became pinned at this divide with retreat rates of -100-200 m/Myr.

Keywords: thermochronology, Apatite Fission Track Analysis, U-Th/He Analysis, passive margin, denudation, Drakensberg, deep borehole v.dimas@pgrad.unimelb.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

STRAIN PARTITIONING AND A DETACHMENT IN THE BROKEN HILL BLOCK, NSW C J . FORBES^ ^ and P.G. Betts^ Vredictive Mineral Discovery Cooperative Research Centre, School of Geosciences, Monash University, Victoria 3800, Australia ^School of Geosciences, Australian Crustal Research Centre, Monash University, Victoria 3800, Australia The Early Proterozoic Broken Hill Block, New South Wales, is a polydeformed terrane where the identification of fold interference patterns and analysis of strain partitioning has been used to constrain the structural evolution (e.g. Marjoribanks et al., 1980; Hobbs et al., 1984). In this study, structural mapping conducted in the Allendale Mine Area in the northern Broken Hill Block has revealed previously unidentified, well-preserved Type 2 mushroom fold interference patterns associated with zones of strain partitioning, which developed during the ca. 1600 - 1590 Ma Olarian Orogeny. The Allendale Mine Area has been subdivided into the western, central and eastern domains, based on differences in lithology and structural geometry. The western domain comprises andalusite-bearing pelites with minor garnet. The structural geometry of this domain is dominated by meso- to macroscale Type 2 mushroom fold interference patterns as the result of fold interference between F2 recumbent folds and F3 upright, --N-S trending folds. The eastern domain is dominated by psammitic units interlayered with minor pelite that contains minor sillimanite and garnet. The structural geometry of this domain is dominated by upright, -N-S trending F3 folds. Recumbent F2 structures were not identified in the eastern domain, however a weak S2 fabric is preserved throughout this domain. The central domain comprises garnet and sillimanite rich pelite dominated sediments. The central domain is a high strain zone defined by an -N-S trending early high-temperature shear zone (informally termed the 'central shear

zone'). Mineral lineations within the shear zone are defined by sillimanite and biotite, with occasional andalusite. Garnet and occasional andalusite porphyroblasts are preserved within the shear zone. The porphyroblasts are wrapped by a mylonitic fabric defined by biotite + sillimanite (retrogressed to sericite) + muscovite + quartz. S-C foliations within the mylonite are sub-parallel. The shear zone boundaries are well defined with the effects of shearing diminishing over a distance of 10 meters at the shear zone margin. The 'central shear zone' separates the western and eastern domains, which, as described, are two areas of differing structural geometry. This raises the question of the role of the 'central shear zone' in the structural evolution of the Allendale Mine Area. Recumbent folds (or nappes) commonly develop in the hangingwall of a basal detachment structure into which strain is partitioned, and over which bulk rock lateral translation has occurred. Within the Allendale Mine Area, the western domain is interpreted as the hangingwall of a detachment structure where recumbent folds have developed. The eastern domain lies in the detachment footwall where recumbent folds have not developed. This accounts for the focus of recumbent F2 folds in the western domain. We suggest that the central shear zone was a detachment shear zone active during D2. Overprinting by upright folds during the D3 event resulted in the development of Type 2 fold interference patterns in the western domain and upright folds in the eastern domain.

Keywords: Fold interference patterns, Non-cylindrical folding, Detachment, Strain partitioning, Broken Hill, Olarian Orogeny, Australia caroline@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

THE STRUCTURAL EVOLUTION OF THE DEAD HORSE SYNFORM, OLARY DOMAIN, SOUTH AUSTRALIA C. LORINI and P. Betts School of Geosciences, Australian Crustal Research Centre, Monash University, Victoria 3800, Australia The Dead Horse Synform is located within the Weekeroo Inlier, of the Olary Domain, part of the Curnamona Province, a complex poly deformed terrane consisting of Palaeoproterozoic to Mesoproterozoic metasedimentary and metavolcanic rocks (the Willyama Supergroup) that have been tentatively interpreted to have been deposited in a developing rift sequence. These rocks were multiply deformed and metamorphosed during the Olarian Orogeny (1600-1590 Ma) and unconformably overlain by the sedimentary successions of the Neoproterozoic Adelaide Rift Complex. The rocks of the Adelaidian succession were later deformed during the Delamarian Orogeny, ca 520510 Ma. The Dead Horse Synform is a relatively tight northeasterly trending fold, which has been interpreted as representing an F1, fold hinge refolded by a later deformational event (Clarke, 1986). My results show that the first deformation event is characterized by a layer parallel fabric, defined by the alignment of biotite and migmatite melts and which has no folding associated with it. In the hinge zone of the Dead Horse Synform this early layer parallel fabric is overprinted by a second-generation axial planar biotite fabric, suggesting that the synform is a second generation F2 structure. The third deformational event is characterized by the development of a

northeast trending styolitic cleavage, produced by the dissolution of rock. There have been no regional folds of this generation recognized although numerous small-scale third generation folds are observed. An earlier generation shear zone defined by migmatite horizons in the lower parts of the Willyama Supergroup stratigraphy is folded about the Dead Horse Synform. The shear zones are characterized by disharmonic folding of melt veins, attenuated melt veins, and a strong foliation defined by the alignment of biotite. When unfolded the shear zones on either limb show the same direction of movement across the region and also appears at many localities to have undergone localized F2 folding which postdates shearing. The significance of this early shear zone is not yet ascertained, although given there is no regional folding associated with them; it is possible they are extensional in origin. The first three deformations are interpreted to have occurred during the Olarian Orogeny. A later, east-west trending fracture cleavage within the region is attributed to the later Delamarian deformation that affected also the rocks of the Adelaide Rift Complex succession. This spaced fracture cleavage is associated with a gentle very open folding within the Dead Horse structure.

Keywords: Curnamona Province, Weekeroo Inlier, Olarian Orogeny, folding, shear zones clorini@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

THREE DIMENSIONAL SLAB STRUCTURE OF THE NORTHWEST PACIFIC MARGIN M.S. MILLER Research School of Earth Sciences, The Australian National University, ACT 0200, Australia Recent studies on slab structure in the northwest Pacific have imaged inconsistent geometries of the subducted ocean lithosphere along the plate margin. Below the Mariana arc portions of the subducted Pacific plate penetrate into the upper mantle vertically while in areas below the Izu-Bonin arc the slab appears to lie horizontally. This large variation in geometry is particularly well visualised in three dimensions using a combination of seismic tomography and earthquake data. In the last 20 years there has been a

considerable amount of research involving seismic tomography and imaging subducting slabs in the Northwest Pacific, but very few have attempted to incorporate relative plate motion to understand the differing geometries and fate of the slabs in 3-dimensions. This multidisciplinary computer based project focuses on the three-dimensional structure and tectonic history of the northwest Pacific plate margin in order to understand the evolution of the subducting Pacific plate.

Keywords: three-dimensions, seismic, tomography, slab, tectonics mmiller@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

QUANTIFYING THE ROLE OF NORMAL FAULT GROWTH, SEGMENTATION AND INTERACTION ON SEDIMENTATION DURING ANCIENT BASIN FORMATION: A CASE STUDY FROM THE LATE CAMBRIAN OWEN CONGLOMERATE, WEST COAST RANGE, WESTERN TASMANIA C.A. NOLL and M, Hall School of Geosciences, Monash University, Victoria 3800, Australia The stratigraphic and depositional architecture of evolving extensional basins is principally controlled by nornnal fault growth through the generation of accommodation space. The history of border fault systems therefore controls the evolution of internal drainage patterns and basin facies distributions. Despite recent advances in the understanding of presentday normal fault growth, quantifying the effect of normal fault evolution on the architecture of ancient sedimentary basins has been largely obscured by post-rift deformation and erosion. The Late Cambrian Owen Conglomerate provides excellent insights into the rift-fill history of an ancient extensional basin, due to rugged, glaciated topography and the exceptional outcrops along the West Coast Range of western Tasmania, and the typically overfilled nature of the basin, which preserves the fault displacement history. Structural traverses have delineated the geometry of the extensional fault system active during deposition of the Owen Conglomerate. The fault system comprises a segmented array of border faults with variable along-strike polarity. Minimum displacements were calculated from present-day stratigraphic thicknesses, and define a roughly symmetric displacement-length profile that resembles that of a single, isolated fault, with maximum displacement (Dmax) located at the centre of the fault array, and decreasing displacement toward the distal

segments. Displacement along the fault system indicates a varied growth history through time. Isolated faulting (Stage 1) occurred during the early stages of rifting, when small fault segments grew in isolation. Stage 1 faults exhibit a Dmax at the centre of each individual segment. Rapid propagation of fault segments to maximum strike length occurred early in the basin history, with only limited interaction and feedback between individual segments. Continued growth faulting (Stage 2) resulted in migration of the locus of maximum displacement as individual segments began to interact and link. Eventual linking of fault segments (Stage 3) occurred during the final stages of rifting, where the overall system exhibits a characteristic, through-going, displacement-length profile. Integration of lithofacies distributions, isopach maps and palaeocurrent data with the structural dataset shows that the stratigraphic architecture is strongly coupled with the development of the border fault system. While the generation of accommodation space adjacent to footwall scarps facilitated the development of a hanging-wall, dip-slope fluvial catchment and axial-through drainage networks, tectonic subsidence also provided a crucial trigger for the onset of marine sedimentation where accommodation space generated by the localised accumulation of displacement outpaced sediment supply.

Keywords: Fault growth, displacement, syn-rift sedimentation, drainage patterns, Owen Conglomerate Christian@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

FORMATION OF ARCUATE OROGENIC BELTS IN THE WESTERN MEDITERRANEAN REGION G, ROSENBAUM^ and G.S. Lister^ ^Australian Crustal Research Centre, School of Geosciences, Monash University, Melbourne ^Research School of Earth Sciences, The Australian National University, ACT 0200, Australia The Alpine orogen in the western Mediterranean region consists of three classic examples of arcuate orogenic belts: the Rif-Betic belt, the Apennine-CalabrianMaghrebides belt, and the western Alps. All these belts contain high-pressure/lowtemperature (HP/LT) rocks of Cretaceous to Oligocene ages, which were exhumed during extensional deformation. The HP/LT rocks are presently exposed in the sole of metamorphic core complexes. The arcuate belts in the western Mediterranean follow the margins of post-Oligocene extensional basins: the Ligurian, Provengal, Algerian, Alboran and Tyrrhenian basins. The floor of these basins consists of attenuated continental crust (in Valencia Trough, the Alboran Sea and the northern Tyrrhenian Sea) or Neogene to Recent oceanic crust (in the Algerian-Provengal basin and the southern Tyrrhenian Sea). The basins have been developed since the Oligocene within an overriding plate of a northwestdipping subduction zone. The widespread extension was simultaneous with the overall convergence motion of Africa with respect to Europe, suggesting that the development of back-arc basins in the western Mediterranean was driven by rollback of a subduction hinge, which was combined with relatively slow convergence rates of Africa-Europe since the Oligocene. We have studied structural relationships within different segments of the western Mediterranean Alpine orogen in order to reconstruct the formation of the arcuate belts in this region. Our reconstruction shows that the arcuate shape of the Rif-Betic and the ApennineCalabrian-Maghrebides belts was obtained during subduction rollback of the African slab in a direction oblique or orthogonal to the direction of convergence. During subduction rollback, allochthonous units of Alpine origin were emplaced in an arcuate fashion in the periphery of the extensional basins. The ages of HP/LT rocks usually predate the formation of oroclinal bending,

suggesting that the HP/LT rocks were inherited from earlier collisional processes. In a lithospheric view, the subducting lithosphere in the western Mediterranean region evolved from a relatively linear NESW-striking slab located south of the European margin, to several narrow slab segments presently found beneath the Alboran region. North Africa and Italy. These remnant slabs are fragments of oceanic lithosphere consumed since the Oligocene, and can account for 98% of the Oligocene oceanic domain. The slab segments are partly detached from the surface and are separated from each other by regions of low velocity anomalies where tearing has occurred. The deepest slab tears are indicated by the absence of highvelocity anomalies down to depths of - 6 0 0 km. Such tears are found between the Alboran slab and the North African slab and between the North African slab and the Calabrian slab. A shallower tear, which is characterised by the absence of lithospheric slab down to depths of - 2 5 0 km, is found in the central Apennines, between the Calabrian slab and the northern Apennine slab. The formation of arcuate belts is therefore the crustal manifestation of lithospheric processes associated with progressive rollback and tearing of subducting slabs. Deep tears occurred where the retreating subduction zone collided with the northern margin of Africa resulting in the incorporation of continental crust at the subduction system. In the Gibraltar and the Calabrian arcs, the existence of narrow oceanic passages enabled further rollback in a direction that was roughly perpendicular to the direction of convergence. These changes in rollback directions could only have occurred after tearing of the slabs. During subduction rollback, these tears accommodated strikeslip motions, leading to an overall 'extrusion' of the Alboran to the west and Calabria to the east.

Keywords: tectonics, Mediterranean, extension, Alpine orogen, subduction rollback, lithosphere gideon@mail.earth.monash.edu.au 42

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

STRUCTURAL EVOLUTION OF THE MINERVA ANTICLINE, OTWAY BASIN, SOUTHEAST AUSTRALIA - INVERSION DURING REGIONAL EXTENSION C.L SCHNEIDER^ K.C. Hill', and N. Hoffman' ^School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia ^3D-Geo, School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia The Minerva anticline, on the eastern margin of the Shipwreck Trough, in the east-central Otway Basin, evolved through Early to Late Cretaceous extension, followed by Late Cretaceous to Recent pulses of compression. It typifies the inversion genesis of many of the hydrocarbon traps located within the Shipwreck Trough. The Pecten and Port Campbell anticlines were similarly formed by the inversion of Early Cretaceous source-rock bearing graben to form Late Cretaceous structural highs and hydrocarbon traps. In this study, onshore to offshore correlation of seismic facies, combined with three dimensional seismic mapping, reveals that the Minerva anticline formed in the hanging wall of an Early Cretaceous, basement-involved, graben-bounding fault. During the Turonian to Santonian, the northeast trending Early Cretaceous graben was buried by sediments, which thickened into a south-dipping fault zone located north and northwest of the Minerva anticline. East-west trending normal faults locally controlled deposition during this time.

Structural style changed in the Campanian as the Early Cretaceous graben-bounding fault was reactivated as a reverse fault. Isopach maps show that during the Campanian to Maastrichtian, sediments thinned onto the nascent Minerva anticline. A northwest trending, fold axis-perpendicular fault set is consistent with minor compression. Similar compressional folding events during the mid-Eocene and MioceneRecent modified and tightened the fold. The timing of the change from extension to compression is enigmatic. Campanian-Maastrichtian compression at the Minerva anticline was synchronous with the local trans-tensional development of the Shipwreck Trough and, more regionally, continued extension accommodated by the Tartwaup-Mussel hingeline, 50 km to the south. The occurrence of only weakly developed unconformities over the Minerva anticline, suggests that the rate of development of accommodation space largely exceeded the sedimentation rate - implying that compressive structural growth occurred during net regional subsidence.

Keywords: basin inversion, seismic interpretation, Minerva anticline c.schneider@pgrad.unimelb.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

A REVISED MODEL FOR CONVERGENCE BETWEEN INDIA AND ASIA V . G . T O Y ' G . S . L i s t e r \ a n d C. D u b o z ^ ^ Research School of Earth Sciences, The Australian National University, ACT 0200, Australia ^ Australian Crustal Research Centre, School of Geosciences, Monash University, Victoria 3800, Australia An accurate description of relative motions between India and Asia provides important boundary constraints for models of the tectonic evolution of this region. The relative motions can only be calculated through a plate circuit of India ^ (Antarctica Africa (Somalia ^ Nubia) North America ^ Eurasia. We have calculated a revised model for this motion using recently published relative rotation data for all links of this circuit. There are correlations between the timing of major tectonic events in the Indian Ocean and Himalayan collision zone and changes in the relative plate velocities. In the new model presented here, the Indian plate undergoes a large westward swerve between 62.5 Ma (anomaly 28n) and 57.9 Ma (anomaly 26n). The apparent India-Asia relative velocity during this period is 21 cm yr"V It is possible that this swerve is artificial and results from inclusion of Antarctica in the plate circuit for times older than 62.5 Ma (as there is no recent description of direct India-Africa motion for these times). If the 62.5Ma position of India is not included, the relative velocity in this period is only 14.0 cm y r \ It is noted that the Mascarene Plateau separated from the western side of the Indian plate at or just before 62.5 Ma, and Deccan Trap volcanism occurred between approximately 69 Ma and 63 Ma. Between 67.7 Ma (anomaly 31n) and 62.5 Ma, the N-S component of relative velocity decreased by approximately 1.5 cm yr~\ This occurred at broadly the same time as emplacement of the Spontang ophiolite

and an associated island arc (Spong Arc), and of a Cretaceous arc preserved near Xiagaze, southern Tibet, from the north, onto the Indian margin. The maximum relative velocity rapidly decreased after 62.5 Ma, reaching a value of 8.6 cm yr"^ by 51.7 Ma (anomaly 23n). Previous authors have suggested that this slowing resulted from the first engagement of Indian and Asian continental crust. N-S convergence velocities reduced to close to present-day values (approximately 4.5 cm yr"^) and relative E-W velocities increased at the same time as initiation of arcperpendicular extension on the South Tibetan Detachment System in the Himalayas at c. 20 Ma. The validity of the plate circuit can also be questioned because there is a mismatch between the relative positions of the northern Indian and southern Asian margins when they are reconstructed to their approximate shapes before collisionrelated shortening. Post-Triassic motion between Asia and Europe is indicated because palaeomagnetic poles from the two areas are not coincident. Palaeolatitude calculations based on the Asian palaeomagnetic poles indicate that the southern margin of Asia prior to shortening was close to equatorial latitudes, agreeing with palaeolatitudes determined from the southernmost Asian Terrane (Lhasa). If this is the case, then most of the Indian crust was stacked up to form the Himalayas, and only approximately 200 km has been ?subducted, far less than has been previously suggested.

Keywords: plate kinematics, plate motion, plate velocity, India-Asia collision, Himalaya, palaeomagnetic, shortening vtoy@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

17'" Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

SESSION FIVE ECONOMIC GEOLOGY and ENVIRONMENTAL STUDIES

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

STRUCTURE AND ALTERATION OF BASALTIC OCEAN CRUST, CAROLINE COVE, MACQUARIE ISLAND S J . LEWIS and G J . Davidson Centre for Ore Deposit Research, Private Bag 79, University of Tasmania, Hobart, 7001 Sub-Antarctic Macquarie Island is an elongate 34km x 3-5km wide exposure of uplifted - 1 0 M a ocean crust, situated 1500km SSE of Tasmania in the Southern Ocean. The emergent crest of a narrow submarine ridge along the Australia-Pacific plate boundary, Macquarie Island is a globally unique ophiolite that hosts the complete spectrum of ocean crust and upper mantle rocks. World Heritage listed because of its exceptional geology, Macquarie Island is the only subaerial exposure of oceanic lithosphere for which the tectonic environment, ridge geometry, and spreading rate are well-constrained. Located in the far SW of Macquarie Island, the Caroline Cove embayment is situated in a highly-faulted, pillow basalt sequence. The local volcanic architecture consists of three domains, each with distinct structural and alteration characteristics. A 1-2m wide, NNEtrending breccia-fault zone forms the boundary between two domains and is interpreted as an axial rift fault. Enhanced permeability along this fault permitted focused hydrothermal fluid flow and resulted in proximal wall-rock alteration. Multiple periods of fault reactivation, consistent with strike-slip to transpressive post-rift tectonism, are inferred from kinematic indicators and clay-rich brecciagouge. Fault reactivation has significantly modified the original structural framework and resulted in the juxtaposition of disparate alteration domains. The Central Alteration Domain (CAD) is a very distinctive fault-bounded wedge of volcanic rocks. A hydrothermal alteration assemblage is well-developed in the aphanitic basalt, although primary textures are commonly preserved. Pervasive, very fine-grained chloritequartz-albite-titanite (+/- pyrite) in the groundmass imparts a bluish-green colour. Veins and hydrothermal breccias comprising abundant quartz-pyrite-chloriteepidote accompany the groundmass assemblage. Chalcopyrite and barite are

minor but locally significant vein minerals. Several vein stages are recognised, with fine-grained pyrite and chlorite-quartz veinlets the earliest-formed. Quartz-pyriteepidote veins are the most abundant vein stage and a diagnostic component of the CAD. They vary widely in thickness (<5mm to 50cm) and overprint the early chlorite-rich matrix and vein alteration. Quartz veins also contain angular, breccia fragments of altered basalt. A minor and late paragenetic stage is restricted to the main fault zone. Consisting of red-brown Fe-hydroxides, this oxidation phase selectively replaces Fe-bearing secondary minerals such as pyrite and chlorite. Basalt alteration in both the Western (WAD) and Eastern Alteration (EAD) domains is highly selective and of lowintensity. Smectite-rich mixed clay assemblages completely replace interstitial glass and rare olivine phenocrysts. Smectite alteration also occurs in tabular plagioclase crystals as veinlets and very fine-grained specks. Groundmass plagioclase and clinopyroxene are relatively pristine, especially in the EAD. Primary Ti-magnetite is commonly altered to microlitic titanite in the WAD basalt. Veins and breccias are sparse and consist of zeolites, prehnite, and calcite in minor faults. The distinct alteration assemblages in each domain imply significantly different hydrothermal fluid conditions. By analogy with ophiolite and other ocean-crust examples, the CAD assemblages likely formed from hot, acidic fluids enriched in Si, S, and metals. These fluids rapidly ascended from the deep crust in rift axis faults, causing intense but spatiallyrestricted wall-rock alteration. In contrast, the EAD and WAD assemblages are interpreted to form during interaction with less-evolved, low-temperature fluids associated with seawater recharge. Future studies will provide further insight into fault-fluid dynamics in the Macquarie Island hydrothermal system.

Keywords: Macquarie Island, ophiolite, basalt, hydrothermal alteration, oceanic faults lewissj@utas.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

THE VOLCANO-SEDIMENTARY AND STRUCTURAL ARCHITECTURE OF THE WILDWOOD PROSPECT, WESTERN LACHLAN OROGEN: A COMPARISON WITH THE STAWELL GOLD DEPOSIT A . L KAUFMAN School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia The Wildwood prospect, western Lachlan Orogen contains strikingly similar volcanosedimentary lithofacies and records comparable structural and metallogenic histories to the world-class Magdala gold deposit, 20 km southeast, in the Stawell goldfields. The aim of this project is to identify and correlate lithologies and structural similarities between the two, and ultimately help constrain the site of potential gold mineralisation within the Wildwood prospect. Volcano-sedimentary lithofacies at Wildwood include three basaltic facies (massive basalt, pillow basalt and monomictic basalt breccia), rare sulphidic mudstone, black finely laminated mudstone, massive and stratified sandstone and felsic intrusions, all of which are similarly observed at Stawell. The massive basalt is non- to weakly vesicular and contains up to 5% vesicles and amygdules that are replaced by calcite, chlorite, feldspar and/or epidote. Pillow basalt is defined by formally glassy basalt, now replaced by actinolite, epidote and chlorite, the margins are up to two centimetres thick. Vesicles and amygdales are concentrated in zones adjacent to pillow margins and secondary silica, actinolite, chlorite, epidote, calcite and biotite commonly fill interpillow cavities. The monomictic basalt breccia is nonstratified and varies in thickness up to 80 metres, the breccia has gradational contacts with the adjacent massive and pillow basalts. The basalt is conformably overlain by the sulphidic mudstone and finely laminated light grey to dark

chocolate brown mudstone, which is similarly observed at Stawell proximal to the basalt. Preliminary findings suggest that Wildwood has significantly smaller amounts of sulphidic mudstone than at Stawell. The mudstone is dominated by polycrystalline quartz and platy metamorphosed clay minerals with minor alteration. This unit grades into a massive and stratified sandstone. Similar brittle and ductile deformation regimes are observed at Wildwood and Stawell, the pre-mineralisation slaty S1 cleavage and the gently east dipping S2 crenulation cleavage at Wildwood correlate with the S2 and S3 fabrics observed at Stawell. The S1 fabric at Stawell has only been observed on the western, topmost portion of the deposit, it has not been observed at Wildwood. Regional metamorphism to midgreenschist facies has preserved mineral assemblages comprised predominantly of actinolite, epidote, chlorite and minor stilpnomelane in all lithofacies at both sites. Although slight lithological and structural differences exist between Stawell and Wildwood both sites exhibit strikingly similar stratigraphy, metamorphic assemblages and comparable premineralisation fabrics. Accordingly, Wildwood is interpreted to have been situated in the same palaeogeographic position as it is today with respect to Stawell, and is recognised to have undergone the same structural evolution as at Stawell.

Keywords: Stawell Goldfields, Magdala gold mine, volcanic facies architecture akaufman@trinity.unimelb.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

STRUCTURAL CONTROLS ON CENTRAL LODE MINERALISATION WITHIN THE MAGDALA GOLD MINE, STAWELL, WESTERN VICTORIA J.A. ROBINSON School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia. The distribution of gold within the Magdala Central Lode System is controlled by multiple episodes of localised reactivation on "early-D4" faults during progressive deformation. The Central Lode System comprises a series of steep west dipping, north-northwest trending reverse faults and shear zones. The shear system is associated with large laminated to massive quartz veins and is hosted within a sulphide-rich volcanogenic rock package on the western flank of the Magdala basalt dome. While the Central Lode System provides a broad control on the mineralisation, the distribution of gold within the lodes is highly variable, with much of the high-grade ore occurring in a number of discrete steeply-plunging masses, or 'ore shoots', within the larger host conduit. Recent mapping within the Central Lode System has identified up to three populations of slickenfibre lineations on fault surfaces within the ore shoots. These lineations indicate three separate transport directions on the faults; south over north, west over east and northwest over southeast. In contrast, fault surfaces in poorly mineralised regions outside the ore shoots are dominated by a single

population of slickenlines with south over north movement senses. Additionally, the ore shoots are characterised by networks of interconnecting faults as well as shear zones localized below major laminated veins. Poorly mineralised regions tend to lack the strong intersection of faults, while shearing is also weak or absent. Gold occurs with arsenopyrite in veinlets overprinting the early D4 laminated veining or associated with arsenopyrite and pyrrhotite with free gold in major shear zones underlying the laminated veins. The faulting and shearing within the high-grade ore shoots is a product of reactivation during multiple episodes of compressive deformation that can be attributed to variations in the direction of principal stress. These changes in the orientation of principle stress, coupled with variations in the orientation of pre-existing faults following the geometry of the underlying basalt contact, result in the focussing of strain into the ore shoots. The additional permeability, which has resulted from multiple episodes of slip on faults in these regions, has allowed for greater volumes of mineralising fluid to focus within the ore shoots, elevating gold grades.

Keywords: Magdala gold deposit, Central Lode System, Ore shoots, fault reactivation j.robinson5@pgrad.unimelb.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

THE COMPOSITION AND STABILITY OF MINE DRAINAGE TREATMENT SLUDGES J. WOOLLARD and J.A. Webb Department of Earth Science, La Trobe University, Victoria 3086 Australia Treatment of mine drainage can result in the production of large amounts of treatment sludges, particularly in the case of acid mine drainage. These sludges are then disposed of in a range of environments including co-disposal with mine tailings and waste rock, and with industrial and/or municipal waste. However, the stability of treatment sludges in these environments is poorly understood. The future management of treatment sludges and their disposal is an important issue for the mining industry. To successfully design disposal solutions, it is necessary to fully understand the nature of the treatment sludges, including their composition and stability. This study investigates sludges from three locations in order to determine the properties that impact most on their safe disposal. Brukunga is located in South Australia and is a pyrite mine. Benambra is a lead and copper mine, while Ballarat is a gold mine, these are both located in Victoria. Neutralization is used to produce the sludge at Brukunga and Benambra, while in Ballarat ground water

is aerated and then allowed to settle in ponds. XRD, XRF and IR were used to determined the overall composition of the samples. Leach tests performed including the US EPA recommended method, TCLP (Toxicity Characteristic Leaching Protocol), SPLP (Synthetic Precipitation Leaching Procedure) and column leach tests. The TCLP simulates co-disposal with municipal and/or industrial wastes. Acetic acid is used as the leaching medium for the TCLP as this represents the acids the sludge is likely to come in contact with in such a disposal environment. In contrast the SPLP simulates leaching where the sludge will come into contact with acidity; this represents co-disposal with waste rock and/or mine tailings. The column leach tests conducted were used to simulate other disposal options, in particular the proposed codisposal of sludge with bio-solids at Brukunga. This test has the additional benefit of assessing the affects of reducing conditions on the sludge stability.

Keywords: acid mine drainage, laboratory, disposal, leach tests jwoollard13@yahoo.com.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

A ROCK-MAGNETIC STUDY OF BACTERIALLY MEDIATED IRON SULFIDE DIAGENESIS ASSOCIATED WITH GAS HYDRATE-BEARING SEDIMENTS J.A. HOLLAMBY and RJ, Musgrave Department of Earth Sciences, La Trobe University, Bundoora, Australia Recent rock-magnetic and geomicrobiological studies of gas hydratebearing sediments have revealed a relationship between bacterial metabolism, solid gas hydrates and associated free methane gas and iron oxide/sulfide diagenesis. The results of these studies have indicated that microbial populations are supported by free methane gas that occurs within, but dominantly below, gas hydrate stability zones. The metabolic processes of these bacteria also utilise the energy potential of the various redox reactions that drive iron oxide/sulfide diagenesis. As a result of these bacterially catalysed diagenetic processes, the magnetic mineralogy of hydrate-bearing sediments will display a variation with depth, and the presence of both gas hydrates and active bacterial populations can potentially be identified by a distinctive rock-magnetic signal. Initial bulk rock-magnetic analyses (hysteresis and susceptibility measurements) have now been completed on over 400 Ocean Drilling Program (ODP) sediment samples recovered from six gas hydrate-bearing sites. Additional XRD and optical examination has also been conducted on a subset of these samples. Geochemical and temperature data collected at each site, which is used in the identification of gas hydrate stability zones, has also been collated. The key aims of these current investigations are to test the viability of rock magnetic analysis as a tool to identify and characterise hydrate-bearing sequences, and to examine the effect of long-term curation on the magnetic signal of ODP samples. Results from the current rock magnetic analyses have been compared to the existing ODP data of these gas hydratebearing zones to determine if there is a

recognisable rock-magnetic record of sulfide diagenesis related to in situ bacterial activity. A comparison of results from two sites, located 300 km apart on the Peruvian Margin and drilled 16 years apart (1986 and 2002), is reported here. Results from previous studies have shown that rock magnetic grain-size and phase indices, as determined from hysteresis and susceptibility studies, display a systematic response across gas hydrate-bearing intervals, and indicate that the fine-grained biogenic iron sulfide greigite, is the most likely magnetic phase surviving/generated within gas hydratebearing sediments. Pyrite, which is a paramagnet, appears to be the dominant iron sulfide phase generated below the base of gas hydrate stability. Initial rock magnetic results from this current investigation also indicate the probable presence of greigite within the gas hydrate stability zones of both sites. Pyrrhotite, as identified via XRD analysis, is also present. At the site drilled in 2002, greigite and pyrrhotite occur across a zone supporting active bacterial populations. A dominantly pyrite-pyrrhotite iron sulfide mineral assemblage occurs below the base of hydrate stability at the earlier drilled site. Comparison of results from the two sites drilled 16 years apart reveals that the magnetic signal of curated ODP samples is diminished when samples are not stored under anoxic conditions. This results from the ready oxidation of greigite when exposed to air, an effect recognised as a major hindrance when undertaking rock magnetic studies on greigite-bearing sediments. This effect therefore impacts on the viability of using rock-magnetic techniques to characterise gas hydrate zones, if samples are not stored under optimum conditions.

Keywords: gas hydrates, sulfide diagenesis, greigite, bacteria. Ocean Drilling Program J.hollamby@latrobe.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

REGOLITH MAPPING AT BENDIGO, CENTRAL VICTORIA, AUSTRALIA A . K O T S O N I S \ B. J o y c e ' , a n d S . C a r e y ' ^ University of Ballarat, Geology Department, VIC 3353 ^ School of Earth Sciences, The University of Melbourne, VIC 3010 This poster summarizes results from regolith-landform mapping conducted on the Bendigo 1:100 000 sheet area recently published by the Geological Survey of Victoria (VIMP Report 77). The regolith in the Bendigo sheet area can be divided into the following regolith landform units (RLUs): Palaeozoic bedrock units with in situ regolith, Cainozoic units of transported regolith including gold mining residue from the 1850s onwards, and Neogene volcanic lava flows. There is also evidence for Cainozoic movement along the major bedrock structures, which have affected weathering profiles, soils preserved on bedrock units, displaced buried leads, and affected modern drainage. Bedrock units occur over metasedimentary rocks of the Castlemaine Group, and over the Devonian granitoids of the Harcourt Batholith and associated contact metamorphic aureole. Weathering profiles are dominated by saprolite of variable thickness with the regolith now preserved on the bedrock controlled by Cainozoic erosion and landscape evolution, and inferred to have begun in the Cretaceous to Early Palaeogene. The landscape history of the Bendigo area prior to this time is poorly preserved, but minor occurrences of Permian glacial deposits indicate Permian glaciation had affected the landscape. Mesozoic deep weathering is not preserved in the study area, which lies several hundred metres below the projected landsurface of central Victoria (Mount Cole, Mount Lonarch, Mount Avoca), indicating deep weathering on the bedrock is post-Mesozoic and probably associated with an eroded Early Cainozoic palaeoplain that developed prior to late Eocene uplift of the Western Uplands. Transported RLUs are poorly preserved in the Western Uplands, but form a flat-lying composite fluvio-lacustrine plain called the Riverine Plain which includes the northern part of the map sheet

area. Although these units are transported units, they also have regolith developed by post-transport in situ weathering. The oldest transported unit is the White Hills Gravel, which forms the earliest known drainage system in the region and was formed as the end product of erosion of the Mesozoic palaeoplain after extensive dissection. Erosion and weathering continued throughout the Early and Mid Cainozoic. All buried leads and deep leads, and the clay rich alluvial deposits at Axedale and Fosterville (Calivil Formation), formed at this time as a response to rapid erosion and downcutting of valleys following late Eocene uplift in the Western Uplands. Rising sea levels in the Late MioceneEarly Pliocene in the Murray Basin backfilled the deep leads and low-lying areas with marine Loxton-Parilla Sands. Synchronous with and following retreat of the sea weathering continued (Karoonda Regolith), and deposition of the fluviolacustrine Shepparton Formation. Extrusion of the Newer Volcanics also occurred at Bald Hill Volcano and along the Campaspe and Coliban river valleys. Quaternary regolith development was minimal, with incision of narrow sinuous streams and deposition of clayey and calcareous aeolian dust mantles associated with Quaternary aridity. The youngest transported unit is associated with historic gold mining residue, and is found capping the present floodplains along creeks draining the historic gold fields of Bendigo. Secondary gold is not traditionally considered as a feature of the Victorian gold province. However, secondary gold at Fosterville occurs in oxidized quartzgold-stibnite veins and shows refinement of primary gold, and deposition of colloform supergene gold. The timing and extent of secondary gold in the landscape is unclear.

Keywords: Bendigo, central Victoria, regolith, landscape evolution, mapping, soils, secondary gold Andrew.Kotsonis@exxonmobil.com

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

THE LAKE BOGA GRANITE, NORTHWEST VICTORIA — URANIUM IN FLUORAPATITE AND ITS IMPLICATIONS FOR SECONDARY MINERALISATION S J . MILLS School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia Department of Mineralogy, Museum Victoria, PO Box 666E, Victoria 3000, Australia^ CSIRO Minerals, Box 312, Clayton South, Victoria 3169, Australia ^ Corresponding address Palaeozoic granitic rocks are widespread across Victoria. While uranium mineralisation is commonly associated with granitic rocks, there are only few occurrences of such mineralisation in Victoria, which include Wycheproof and Glen Wills. The Lake Boga Granite is unique in Victoria for its assemblages of copper and uranyl phosphates within the granite, including two recently described new minerals, the calcium uranium phosphate, ulrichite and the calcium copper bismuth phosphate, bleasdaleite. The Lake Boga Granite is also noted for its occurrence of large gemmy fluorapatite crystals found in miarolitic cavities. The mineralogy of the Lake Boga granite consists of orthoclase, which exhibit perthitic textures, plagioclase, quartz, muscovite, biotite, black tourmaline (schorl) and sporadic accessory minerals such as apatite and zircon. The question arises as to what caused this apparent simple mineralogy to yield the array of secondary minerals which make this locality unique. The fluorapatites are the key to this story. Various varieties of fluorapatite were selected for cathodoluminescence, element mapping and microanalysis studies. The cathodoluminescence (CL) mapping revealed intricate growth structures and

banding on a scale, which has not previously been reported in the literature. Elemental mapping aided the CL mapping to show compositional banding of Mn, Sr and U with abundances ranging from 0 - 4 wt %. Inclusions also discovered in the fluorapatites were uraninite, monazite(Ce), allanite-(Ce), cheralite-(Ce), various sulphides and several Al and Fe phosphates. Interestingly the monazite(Ce), allanite-(Ce) and cheralite-(Ce) did not contain any detectable uranium, leaving uraninite as the only uraniumbearing primary mineral so far found at Lake Boga. Small grains (<50|jm) of primary uraninite were discovered throughout the granite along with inclusions of monazite(Ce) and zircon with varying amounts of U and Th. U-bearing fluorapatites with uraninite inclusions, together with uraninite, U-bearing monazite-(Ce) and zircon in the granite, are the source of U for the ulrichite, saleeite and torbernite following weathering. The dissolution of the fluorapatites and uraninite by acid groundwater is likely to have occurred during a weathering phase in the Late Pleistocene (-125,000 ka) confirmed by U Th disequilibrium dating of the secondary U minerals.

Keywords: Uranium, fluorapatite, Lake Boga, granite, uraninite, saleeite, torbernite, ulrichite. Pleistocene weathering smills@museum.vic.gov.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

THE GEOLOGY, AGE, NEAR SURFACE FEATURES, AND MINERALOGY OF THE MERLIN KIMBERLITE FIELD, NORTHERN TERRITORY, AUSTRALIA W.R.H. RAMSAY', A. Hell', G. Reinberger' and S. Pooley' ^School of Ecology and Environment, Deakin University ^Merlin Diamonds Pty Ltd The Merlin kimberlite field is located in the southern McArthur Basin, NT. The field comprises twelve single to bifurcating kimberlite pipes and two exposed sandstone breccia pipes, which cover an area of 10 x 5 kms. These kimberlites intrude a sequence of flat lying Proterozoic shelf sediments, the youngest being the Neoproterozoic Bukalara Sandstone. A localised and restricted Cenomanian to Aptian marine in-fill sequence and thickened Tertiary weathering profile overlie and 'cork' all the kimberlite occurrences except the E. Mu pipes to the NNE. These in-fill sequences comprise a basal pebble-cobble conglomerate containing belemnite fossils overlain in turn by bioturbated quartz litharenite sandstone and claystones. Preservation of this sedimentary sequence indicates postemplacement consolidation and subsidence of up to 42 m within individual kimberlites. This subsidence is regarded as relating dominantly to Tertiary solution weathering. 4oAr/39Ar, Rb-Sr, and K-Ar dating of phlogopites derived from various textural phases within five of the kimberlite pipes give a consistent emplacement age of Middle Devonian (352±4 - 382±2 Ma, mean 371 Ma). Texturally each kimberlite contains numerous textural phases representing separate and distinct intrusive events. Fourteen individual textural phases have been recognised with up to seven separate phases forming in any one diatreme. Within this assemblage three major petrogenetic-textural phase groups are recognised namely volcaniclastic kimberlite breccia (VKB), micro-breccia volcaniclastic kimberlite (mbVK), and volcaniclastic kimberlite (VK). These three major textural phase groups exhibit sharp contacts accompanied by thin carbonate selvages and veining. The magmatic phases (VK types) including some mica-rich phases, represent the initial and more passive intrusive stages containing a high percentage of primary mineral phases (5-60vol%) and a low percentage of crustal-derived xenocrysts and xenoliths. The following intrusive stage (mbVK-type) contains a high percentage of

quartz xenocrysts (>30 vol %), low percentage of xenoliths (<5 vol %), rare pelletal lapilli, and uncommon VK-type autoliths. Primary mineralogy is highly altered having undergone serpentinisation, chloritisation, and carbonatisation. Ferruginisation and silicification are common in near-surface bodies. Two populations of pseudomorphed olivines (5-45 vol%) are replaced by serpentine and carbonate. Phlogopite (5-35 vol%) occurs as euhedral and tabular phenocryst and groundmass phases, which may display poikilitic textures with spinel. Other primary phases include macrocrystic chromite (Cr/Cr+AI 0.2-0.95, MgO 8-17 wt%, TiOa 0-4.3 wt%), pyrope garnet (Cr203 2-12 wt%, CaO 1-7 wt%), apatite, and possibly rare picro-ilmenite. No evidence of perovskite, clinopyroxene, or monticellite was observed. Groundmass includes phlogopite ( CrsOs 0-1.79 wt%, TiOs 0.11-4.99 wt%), apatite, and spinel. Bulk rock geochemistry of Merlin kimberlite mostly conforms to Group 1 kimberlites compared to Group 11 kimberlite (orangeite) and Australian lamproites. On a CaO vs MgO plot Merlin kimberlites show a tendency to higher CaO/MgO ratios than shown for the Group 1 kimberlite field. Average trace elements (ppm) Sr 638, Zr 167, Y 110, and Nb 234 compare with other kimberlite provinces. Chondrite normalised REE patterns are strongly LREE enriched with distinct parallel trends and a marked Ho anomaly. Pyrope garnet and macrocrystal compositions indicate deep sampling or crystallisation within the diamond stability field suggesting that all pipes have the potential to host diamonds. In addition groundmass chromites are compositionally consistent with either diamond inclusion compositions or a second population which falls outside. These contrasting populations may relate to differing melt compositions reflecting varying pressure, temperature, and/or melt residence times prior and during emplacement.

Keywords: diamonds, Merlin field, emplacement age. Cretaceous shelf sediments, mineralogy, geochemistry, Bukalara Sandstone, Northern Territory Ramsayr@deakin.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

A LABORATORY STUDY OF THE CONDITIONS GOVERNING IRON PRECIPITATION WITHIN ANOXIC LIMESTONE DRAINS S. SANTOMARTINO and J.A. Webb Department of Earth Sciences, La Trobe University, Victoria 3086 Australia Anoxic Limestone Drains (ALDs) have been widely used in the passive treatment of acid mine drainage (AMD), but their effectiveness has often been less than anticipated. Iron hydroxide often precipitates around limestone particles, reducing limestone dissolution and therefore the neutralising ability of the ALD. To determine the conditions under which iron hydroxide precipitates, a small-scale laboratory ALD system was built to enable a detailed investigation of the location, distribution and chemical nature of Fe precipitates within the drain. For one experiment, a mixture of limestone and quartz was introduced to the drain to assist in the determination of the key mechanism governing iron precipitation. Synthetic anaerobic acid mine drainage containing Fe^"" ( - 1 3 0 ppm), S O / ' and H"' was pumped at a rate of 30 mL/min up a 90 cm tall, 15 cm diameter vertical column filled with limestone gravel of 98% purity. Three sampling ports were fitted at equal intervals along the column; water was periodically extracted for analysis at the sampling ports

over an 11-hour period. Experiments were run at influent pH levels of 2 and 4. Results show that acid neutralisation to pH greater than 6 occurred at the inflow end of the drain. The greatest amount of iron precipitation (19.5%) also occurred in this area. The lack of iron precipitation on the quartz surfaces in the quartz/limestone mixture indicates that neutralisation is the key mechanism for the precipitation of iron hydroxide on limestone particles. A pe-pH stability diagram derived for the laboratory ALD system indicates that ALDs will not be effective for AMD with pH < 1.5. At these pHs, the lower water stability limit prevents the pe from being sufficiently reduced to prevent iron precipitation upon neutralisation. To avoid iron precipitation altogether within an ALD, influent AMD must have a pH > 2. Influent waters with pH 2 require a pe of - 2 (Eh: -118.4 mV) to avoid Fe precipitation upon neutralisation. Influent waters of pH 4 require a pe between - 2 and -4.

Keywords: acid mine drainage, passive treatment, iron hydroxide, ferrihydrite, neutralisation slsantomartino@students.latrobe.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

GEOCHEMISTRY AND ARCHITECTURE OF THE NiS DEPOSIT, RIWAKA COMPLEX, GRAHAM VALLEY, WEST NELSON, NEW ZEALAND R. SMITS, S.W, Beresford, and B. Schaefer School of Geosciences, Monash University, Victoria 3800, Australia The Riwaka Complex is an ultramafic to mafic intrusion that is about 45km long and 1km wide. The intrusion was emplaced into sedimentary units of the Takaka terrane at 385Ma(K-Ar). Work on the Riwaka Complex has been centred on the economic potential for a NiS deposit. Present work has failed to identify economic NiS mineralisation. The units making up the Riwaka Complex vary from Peridotites through to leucogabbro with sub-vertical layering.

The intrusion is linear, with a concentration of ultramafic rocks to the western side of the intrusion, and mafic rocks to the eastern side. The sub-vertical layering appears to be the product of a number of magma impulses from a fractionating magma chamber. This study will look at the architecture and geochemistry of a NiS deposit and assess the role of dynamic emplacement on NiS genesis.

Keywords: Riwaka Complex, NiS genesis, igneous petrology, geochemistry Russell.Smits@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

PHOSPHOROUS FIXATION IN ACID SULPHATE SOILS OF THE COODE ISLAND SILT, CENTRAL VICTORIA D X V U \ J. W e b b \ a n d P. S a l e ' ^Department of Earth Sciences, La Trobe Unviersity, Vic 3086 ^Department of Agriculture, La Trobe Unviersity, Vic 3086 Acid sulphate soils (ASS) are rich in pyrite, and commonly form in estuarine and very shallow marine environments. When drained, the pyrite is oxidized to sulfuric acid, causing a severe fall in pH, usually to <4. In these low pH conditions, aluminium and iron become relatively mobile and can form insoluble compounds with phosphate. As a result, phosphate in ASS is typically unavailable to plants, causing serious problems for agriculture in these soils. To understand the mechanism of phosphorous adsorption in ASS, six fresh (unoxidised or only slightly oxidised) samples of the Holocene Coode Island Silt were collected from a single site in the Yarra Delta; this unit is widely recognised as having acidification problems after exposure to the atmosphere. On average, the Coode Island Silt consists of silt-sized quartz with - 1 7 % clay (mostly kaolinite, with some montmorillonite) and 4-4.5% organic matter. The field pH is 4-6.5, but on oxidation this drops to 2-3, due to oxidation of pyrite (present as - 0 . 6 % S in the samples). The Titratable Sulphidic Acidity (TSA) is - 4 0 0 mol HVtonne, illustrating the high potential acidity of the Coode Island Silt.

Four subsamples of each of the six samples were subjected to un-, slightly, moderately, and extremely oxidizing conditions, and then analysed for soil phosphorous buffering capacity (PBC; indicating the amount of P available for plant uptake), as well as exchangeable and oxalate-extractable Al and Fe, which were compared with total Al and Fe analyzed by XRF. Oxalate-extractable Fe% is almost the same as the total Fe%, indicating that the Fe is present as poorly crystalline phases, and exchangeable Fe is strongly correlated with PBC. Oxalateextractable Al% is much less than total Al%, verifying that Al is present mostly as crystalline clays, but exchangeable Al is also strongly correlated with PBC. Nevertheless, the phosphate adsorption resulting from the great increase in exchangeable Al and Fe never reaches the maximum possible under the experimental conditions. It may be that the progressive breakdown of organic matter within the samples by the acid released during oxidation forms organic species that can react with the exchangeable Fe and Al, preventing their adsorbing all the available phosphate.

dtvu@students.latrobe.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

THE 440 MA MINERALISING EVENT IN THE LACHLAN FOLD BELT: RESULT OF A TECTONIC MODE SWITCH? L M . A . V O S \ G . S . L i s t e r ^ a n d F.P. Bierlein^ Vmd*CRC, School of Geosciences, Monash University, Victoria 3800, Australia ^Research School of Earth Sciences, The Australian National University, ACT 0200, Australia The Lachlan Fold Belt in southeastern Australia is host to a variety of mineral deposit types and is generally recognized as being an area of major gold endowment. Mineralisation ages of some of the largest gold deposits in this belt, such as Bendigo, Ballarat and Cadia, have all been dated at --440 Ma, but the spatial relationships between deposits that occur in different segments of the orogen and are of diverse character are poorly understood. Gold deposits in the eastern and western parts of the Lachlan Fold Belt appear to have formed in distinct tectonic settings with characteristic ore mineral, alteration and host rock assemblages. Gold deposits in the western Lachlan Fold Belt are dominated by lode-Au style mineralisation, typical for turbidite or slate belt-hosted provinces. In contrast, gold deposits in the eastern Lachlan Fold Belt are characterized by porphyry Au-Cu style mineralisation related to magmatic arc development in a supra-subduction environment. The nature of these deposits has previously been assessed only in terms of mechanisms that control ore genesis at the deposit scale. The present interpretations of the tectonic framework for the Lachlan Fold Belt at around 440 Ma cannot explain the remarkable coincidence in gold mineralisation at this time across the belt. We present a model for 440 Ma gold mineralisation in the eastern Lachlan Fold Belt and explore the effects of the suggested mechanism that controlled metallogenesis there on the western Lachlan Fold Belt.

around 480 Ma and ended abruptly at 440 Ma. The final stages of arc magmatism are characterized by a distinct K-rich (shoshonitic) composition, which are found to be contemporaneous with the formation of Au-Cu deposits. Metasomatised mantle is considered the source material for the shoshonitic magmas and, by inference, as a source for the ore forming fluids. Postsubduction partial melting of (parts of) stalled slabs, or the associated metasomatised mantle wedge (as a result of slab foundering) may generate highly oxidised magmas and destabilize mantle sulphides to release copper, gold and PGE, which would then become available for transport to the upper crust. This mechanism is suggested for the simultaneous generation of shoshonitic magmas and ore deposits in the eastern Lachlan Fold Belt. We hypothesize that a tectonic mode switch, whereby subduction along the eastern margin of Australia had either ceased or changed its orientation, took place in the Lachlan Fold Belt at --440 Ma. This tectonic mode switch is apparent from major changes in the nature of magmatism, sedimentation and deformation that occurred at around 440 Ma. These changes include cessation of arc magmatism in the Macquarie Volcanic Arc and termination of accretion along the Narooma accretionary complex. Based on these changes, we suggest that a tectonic mode switch from overall shortening to extension took place across the Lachlan Fold Belt as a result of the onset of rollback of a cratonward-dipping subduction zone east of the Pacific margin of Gondwana. Similarly, this overall change from shortening to extension in the Lachlan Fold Belt at - 4 4 0 Ma allowed upward migration of ore-forming fluids to mid-crustal depths and entrapment in dilation zones in the western Lachlan Fold Belt.

In the eastern Lachlan Fold Belt, porphyry Au-Cu deposits dated at - 4 4 0 Ma are associated with Ordovician potassic igneous rocks belonging to the Macquarie Volcanic Arc. The Macquarie Volcanic Arc is considered to be part of an intra-oceanic arc formed above a cratonward-dipping subduction zone that was active from Early Ordovician to earliest Silurian times. Arc magmatism started in the Early Ordovician

Keywords: 440 Ma, Lachlan Fold Belt, mineralisation, tectonic mode switch ivovos@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

STRUCTURAL AND METALLOGENIC CHARACTERISTICS OF GOLD DEPOSITS IN THE AMANDA BEL GOLDFIELD, BROKEN RIVER PROVINCE, NE QUEENSLAND, AUSTRALIA L M . A . V O S \ F.P, B i e r l e i n \ a n d G.S. Teale^ ^ pmd*CRC, School of Geosciences, Monash University, Victoria 3800, Australia ^ Teale & Associates Pty Ltd, Adelaide, South Australia The Amanda Bel Goldfield is situated in the Camel Creek Subprovince of the Palaeozoic Broken River Province in northeastern Queensland. The goldfield is host to a number of gold deposits that include the Camel Creek, Golden Cup, Red Gold, Airport (AP) and Spartan deposits. Over 90,000 oz of gold have been extracted from this area since 1989, which makes it a significant producer of gold in Eastern Australia and a potential area for future exploration. Structural and metallogenic features of the Camel Creek, Golden Cup and Red Gold deposits are presented here and form the basis for addressing their relationship within the larger-scale tectonic framework, including comparisons with the adjacent Hodgkinson Province. Mineralised zones in the Amanda Bel Goldfield generally occur along a northeastern trend and are hosted by strongly deformed Late Silurian to Early Devonian meta-sedimentary rocks of the Greenvale and Kangaroo Hills formations. Host rocks (carbonaceous shales and greywackes) are generally silicified and, adjacent to quartz veins, white micas, chlorite and ankerite form the major alteration minerals. Gold mineralisation is associated with iron- and base metalbearing quartz veins. Various styles of quartz veins are documented and include deformed bedding-parallel veins, stockwork veins, planar sheet veins, breccia veins and quartz-carbonate veins. The various quartz vein assemblages are closely linked to the structural history of the host rocks. A sequence of at least 3 major deformation events can be recognised in the gold deposits of the Amanda Bel Goldfield. Di is represented by isoclinal folds and a near-vertical, anastomosing cleavage fabric trending NESW. D2 is associated with refolding of Fifolds and the development of a co-planar cleavage along a NE-SW trend. D3 is

attributed to a stage of SW-NE shortening and related to moderately ( - 6 0 ° ) SWdipping thrust faults along a strike of 330340. Low-grade syn-Di mineralisation occurs in quartz-stibnite±gold lenses and boudins in carbonaceous shale horizons that have been folded during D2. Shear zones parallel to the S2 cleavage host narrow, discontinuous quartz veins and stockworks that are mineralised. D2 mineralisation consists of quartz-stibnitearsenopyrite lenses within auriferous carbonaceous shales. Barren breccia veins are located along thrust planes that are associated with D3. En echelon arrays of laminated, quartz-carbonate spur veins are attributed to late-stage D3 deformation. The deformation events recognized in the Amanda Bel Goldfield are characteristic for the deformation history of the Camel Creek Subprovince. Di is assigned an Early Devonian age, where D2 could be Late Devonian and D3 thrusting occurred in the Early Carboniferous. The accuracy of the age for these events can be tested against absolute age data for mineralisation that will be produced from future work, which will also include constraints from sulphur isotopes and fluid inclusions. Based on the present study and previous work by other authors, the metallogeny of the Broken River Province can be used as a key to tectonic evolution, similar to studies recently undertaken in the Lachlan Fold Belt of southeastern Australia. In addition, this research can be compared with similar data gathered from goldfields in the Hodgkinson Province. This will provide further insight into the tectonic evolution of the (northern part of the) Tasman Fold Belt System and aims at solving some of the controversies that include the tectonic setting of gold deposition (i.e., back-arc vs. fore-arc), the source of ore-bearing fluids (i.e., metamorphic vs. magmatic) and the control of major faults on mineralisation.

Keywords: structure, metallogeny, Broken River Province, tectonic framework ivovos@mail.earth.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

FERTILITY OF THE AGNEW KOMATIITE, AGNEW, WESTERN AUSTRALIA H.M. WALLACE, S. Beresford, and R.A.F. Cas School of Geosciences, Monash University, Victoria 3800, Australia The Agnew-Wiluna Belt (from Wiluna to Leinster) hosts some of the largest komatiite-hosted Ni deposits in the world (eg. Mt Keith, Perseverance). Recent exploration efforts have focused on the komatiite units around Agnew in the southwestern area of the belt with the hope that they may represent a continuation of the mineralised komatiite units. Presently, no economic Ni-Cu(PGE) mineralisation has been identified. Reasons for this heterogeneous distribution of Ni-Cu-(PGE) mineralisation are undetermined. Due to poor outcrop and structural complexity in the belt, komatiite units have not been confidently traced along strike between the northern and southwestern areas of the belt. Hence, the possibility exists that the Agnew komatiite is genetically unrelated to the mineralised komatiites. Another possibility is that komatiite units are oogenetic but they experienced different histories of crustal interaction and sulphur saturation. This study describes characteristics of the komatiites near Agnew and proposes causes for the lack of Ni-Cu-(PGE) mineralisation. The Agnew sequence is characterised by mafic volcanic footwall units overlain by a thick komatiite, which in turn is overlain by several volcaniclastic units. The Agnew

komatiite is subdivided by mineralogy and chemistry, into a large cumulate basal unit and [commonly separated by a shear zone] an upper unit of thin flows. The upper unit is characterised by multiple stacked thin spinifex and cumulate flows. Relative to the Ni-rich komatiites in the northern portion of the belt, the Agnew komatiite has lower Ni and is locally chromite bearing. Due to extensive shearing of the upper, basal and internal unit contacts, the emplacement origin of the basal komatiite unit is contentious. However, the thickness of the basal Agnew komatiite unit and the sheet-like architecture suggests that the lower komatiite unit may have been emplaced as a sill. Preliminary results such as geochemistry and the sulphide-poor underlying footwall unit suggests that the Agnew komatiite did not assimilate crust or reach sulphide saturation. The extensive tranquil sheet emplacement and lack of crustal interaction are prime reasons for the lack of mineralisation. Agnew komatiites are considered to represent the extreme example of an infertile komatiite belt/sequence, and an excellent case study in the volcanological and geochemical variation in so called fertile provinces.

Keywords: Archaean, komatiite, nickel, infertile, chromite hwal4@student.monash.edu.au

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

Geological Society of Australia Abstracts 70

Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

Geological Society of Australia Abstracts 70

17^ Victorian Universities Earth Sciences Conference, Monash University 5 September 2003

Index of Authors B

Beresford, S.W.. Betts, P.G Bierlein, F.P BOYD, G.A Brown, R.W

56, 60 35, 38, 39 58, 59 15 37

Carey, S. Cas, R.A.F CHEESMAN, A.R CORBET, LA

.52

May, D MILLER, M.S... MILLS, S.J Moresi, L MULLER, B.J... Musgrave, R.J. N NOLL, C.A

....7

PIPER, K.J Pooley, S 47 37 44

RAMSAY, W.R.H Reinberger, G ROBINSON, J.A ROSENBAUM, G

17 38 33 35

Giordano, G GORTON, J.T GROVER, M u H

9 16 25

Hall, M HASSELL, T Hell, A Hergt, J Hill, K.C HOCKING, M.J Hoffman, N HOLLAMBY, J.A HOUSE, E

41 4 54 8 43 5 43 51 6

3 29 59 44 12

V 4 52

Viramonte, J.G VOS, I.M.A VU, D.T

3 58, 59 57

48 34 8 52

WALLACE, H.M Wallace, M.W WATTIE, J.L Webb, J.A Williams, 1 Wilson, C.J.L WOOD, D.G Woodhead, J WOOLLARD, J

1 L

LABERGE, R.D LAING, A LEACH, A.S LEWIS, S.J LIM, E.-P Lister, G.S Liu, L LORINI, C

57 55 56 43 20 21 11 26, 28 28 56

T f

TAIT, M.A TANAKA, C Teale, G.S TOY, V.G TROWBRIDGE, R

KAUFMAN, A.L Kelsey, D KEMP, R KOTSONIS, A

54 54 49 42

S Sale, P SANTOMARTINO, S Schaefer, B SCHNEIDER, C.L SCHWARTZ, LR.S SEEGETS-VILLIERS, D.E. SHAW-STUART, A. Simmonds, 1 Smith, 1 SMITS, R

Jackson, P Joyce, B

F FITZGERALD, E.M.G FORBES, C.J FREEMAN, J FRY, K

19 54

Q QUINN, C

E Edwards, P

D Davidson, G.J DIMAS, V.-A Duboz, C

33 40 53 33 10 51

9 27 18 47 26 36, 42, 44, 58 16 39

60 18 30 ..4, 6, 16, 29, 30, 50, 55, 57 8 34 36 8 50

Y A Xu, G