Geological Society of Australia
ABSTRACTS Number
90
22"d Victorian Universities Earth and Environmental Sciences Conference 26th September 2008 The University of l\4elbourne
VUEESC Victorian Universities Earth and Environmental Sciences Conference 26 September 2008
Program & Abstracts
Hosted by: School of Earth Sciences The University of Melbourne
Editors:
Kim S. Ely Alison Fairnnaid Stefan Frei
Geological Society of Australia Abstract Volume Number 90
Geological Society of Australia Abstracts Number 90 Victorian Universities Earth and Environmental Sciences Conference September 2008
Editors: Kim S. Ely, Alison Fairmaid and Stefan Frei
ISSN 0729 011X © Geological Society of Australia Incorporated, 2008
Recommended citations: Ely, K. S., Fairmaid, A. and Frei, S. (eds), 2008. Victorian Universities Earth and Environmental Sciences Conference. Geological Society of Australia Abstracts Number 90, p. 37. Jakica, S., 2008. The erosion rates of the Darling Escarpment, Western Australia. In: Ely, K. S. Fairmaid, A. and Frei, S. (eds). 22"^ Victorian Universities Earth and Environmental Sciences Conference. Geological Society of Australia Abstracts Number 90, p. 32.
Copies of this publication may be obtained from: The Geological Society of Australia Incorporated Suite 706, 301 George Street Sydney NSW 2000 Australia
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I Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
PROGRAM 8.30
Registration opens
9.00
Welcome and opening remarks: Janet Hergt
9.15
Keynote address: John Moreau Theme 1: Hydrogeology
9.35 9.50
Chair: Fabian Kohlmann
Matt Currell: Geochemistry of groundwater with high fluoride concentrations in the western Yuncheng Basin, north China Fiona Glover: Inland acid sulphate soils: a study of three wetlands along the Murray River floodplain
10.05
Sharon Honicke: The hydrogeology of the Upper Campaspe Deep Lead, north central Victoria
10.20
John Sharpies: Modelling of groundwater recharge on a small scale (paddock) using MIKE SHE
10.35
11.00 11.15 11.30 11.45
12.00 12.15 12.30
Morning Tea (Poster session run concurrently)
25 minutes
Theme 2: Economic and Mine Geology Chair: Sara Jakica Mark Lindsay: Determining porphyry copper prospectivity in a North American mining district by integrating geological and remotely sensed data into weights-of-evidence and fuzzy logic models Andrew Nelson: Remediation of mine discharge water at the Glen Wills historic mining region Anisur Rahman: Distribution and mobility potential of arsenic in soil profiles in proximity to an abandoned gold mine, Victoria, Australia Vanessa Di Florio: The mobility of titanium in hydrothermal systems in the Mount Isa Inlier, northwest Queensland Theme 3: Geothermal Systems Chair: Sara Jakica LiesI Cristanelli: Heat flow data in the Murray Basin, South Australia: relationship of high heat zones to geological events and granitic inliers Sarah Wright: Heat flow in the Latrobe Valley: the role of thermal conductivity and heat refraction Lunch Break (Poster session run concurrently) Theme 4: Palaeontology
45 minutes Chair: Estee Woon
13.15
Brian Choo: A basal actinopterygian fish from the Middle Devonian Aztec Siltstone of Antarctica
13.30 13.45
Alice Clement: A new genus of lungfish from the Late Devonian (Frasnian) of Western Australia Tim Holland: High resolution CT-Tomography of fossils: the braincase of Gognasus andrewsae (Sarcopterygii, Tetrapodomorpha) Theme 5: Climate Chair: Luke Garde
14.00
John Allen: An improved and updated climatology of explosive cyclogenesis
14.15
Dean Sgarbossa: Australian easterly dips
14.30
Afternoon Tea (Poster session run concurrently) Theme 6: Earth dynamics and chemistry
15.15
30 minutes Chair: Linden Ashcroft
Kim Ely: Deformation of a subducting slab: the variable boundary conditions of a slab tear Chris Folkes: The application of micro-analytical techniques in understanding the evolution of large silicic systems; evidence from Cerro Galan Caldera, northwest Argentina
15.45 16.00 16.15
Sara Jakica: The erosion rates of the Darling Escarpment, Western Australia Ryan Koch: The structural history and architecture of the covered antiformal stack, Heathcote Fault Zone, Victoria Maddy Willcock: The dynamic multi-phase eruptive processes and associated deposits of the Argyle (AK1) lamproite volcanic system, Halls Creek Mobile Zone, Western Australia
16.30
Awards and closing remarks
17.00
Drinks and nibbles in the tea room
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
SPONSORS
Geological Society of Australia
GOLD SPONSORS The University of IVIelbourne School of Earth Science THE UNIVHRSITY OF
MELBOURNE
^ MONASH University
Monash University
Science
Geological Society of Australia Victoria Division VICTORIA DIVISION
Department of
Department of Primary Industries
Primary Indiistries
Petroleum Exploration Society of Australia
Colder Associates
IV
i
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
Geological Society of Australia Abstracts 90
INTREPID
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Intrepid Geophysics S
E^^onMobil
ExxonMobil
SILVER SPONSORS
GeoViSIO
International Association of Hydrogeologists (Australian Chapter)
BRONZE SPONSORS
LATROBE
UN I VERSITY
La Trobe University Faculty of Science, Technology and Engineering
E The University of Melbourne Earth Sciences Postgraduate Group
The Australian Meteorological and Oceanographic Society
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
Contents THEME 1: Hydrogeology Geochemistry of groundwater with high fluoride concentrations in the western Yuncheng Basin, north China M. CURRELL
2
Inland acid sulphate soils: a study of three wetlands along the Murray River floodplain F. GLOVER
3
The hydrogeology of the Upper Campaspe Deep Lead, north central Victoria S. HONICKE
4
Modelling of groundwater recharge on a small scale (paddock) using MIKE SHE J. P. SHARPLES
5
The hydrogeology of the Lake Connewarre Complex T. A. KEOGH
6
THEME 2: Economic and Mine Geology Determining porphyry copper prospectivity in a North American mining district by integrating geological and remotely sensed data into weights-of-evidence and fuzzy logic models M. D. LINDSAY 8 Remediation of mine discharge water at the Glen Wills historic mining region A J. NELSON, J. A. Webb & D. Arne
9
Distribution and mobility potential of arsenic in soil profiles in proximity to an abandoned gold mine, Victoria, Australia A RAHMAN, K. Dowling & F. Zohora
10
The mobility of titanium in hydrothermal systems in the Mount Isa Inlier, northwest Queensland \/. DIFLORIO
11
^^Ar/^^Ar dating and fluid noble gas constraints on orogenic gold mineralisation in Victoria, Australia A FAIRMAID, D. Phillips, M. Kendrick & B. Fu
12
The occurrence of pyrometamorphic rock in the Dawson coal mine, central Queensland P. W. HOILES, P. W. Whitehead &B. G. Lottermoser
13
THEME 3: Geothermal Systems Heat flow data in the Murray Basin, South Australia: relationship of high heat zones to geological events and granitic inliers L CRISTANELLI
16
Heat flow in the Latrobe Valley: the role of thermal conductivity and heat refraction S. WRIGHT, B. Harrison & M. Sandiford
17
VI
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
THEME 4: Palaentology A basal actinopterygian fish from the Middle Devonian Aztec Siltstone of Antarctica B. CHOO
20
A new genus of lungfish from the Late Devonian (Frasnian) of Western Australia A M. CLEMENT
21
High resolution CT-tomography of fossils: the braincase of Gogonasus andrewsae (Sarcopterygii, Tetrapodomorpha) T. HOLLAND
22
Australian crawl: evidence for the fish/tetrapod transition in Australia T. HOLLAND
23
THEME 5: Climate An improved and updated climatology of explosive cyclogenesis J. ALLEN
26
Australian easterly dips D. SGARBOSSA, M. Reader, R. Wardle & J. Kepert
27
Reducing the uncertainty in AR4 rainfall projections for the Murray-Darling Basin E. CHANDLER
28
THEME 6: Earth Dynamics and Chemistry Deformation of a subducting slab: the variable boundary conditions of a slab tear K. S. ELY&M. Sandiford
30
The application of micro-analytical techniques in understanding the evolution of large silicic systems: evidence from Cerro Galan Caldera, northwest Argentina C. FOLKES, S. de Silva, R. Cas, H. Wright & J. Viramonte 31
8
The erosion rates of the Darling Escarpment, Western Australia S. JAKICA
32
The structural history and architecture of the covered antiformal stack, Heathcote Fault Zone, Victoria R. D. KOCH
33
The dynamic multi-phase eruptive processes and associated deposits of the Argyle (AK1) lamproite volcanic system, Halls Creek Mobile Zone, Western Australia M. A. W. WILLCOCK
34
The geochemistry of the west Australian, West Kimberley Province lamproites R. CHESLER, J. Hergt, D. Phillips & R. Maas
35
The age, geochemistry and petrogenesis of an unusual alkaline intrusion in the western Pilbara Craton, Western Australia E. MATCH AN, J. Hergt, D. Phillips & S. Shee 36 Author index
37
VII
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
ORGANISING COMMITTEE Convenor Kate Gordon
Website Ben Harrison Kate Gordon
Abstract volume and program Kim Ely Alison Fairmaid Stefan Frei
Sponsorship Erin Matchan Peter Hoiles Elise Chandler
Publicity Angela Bush
Catering Campbell Watson
VIII
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
Theme 1
Hydrogeology
s
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
GEOCHEMISTRY OF GROUNDWATER WITH HIGH FLUORIDE CONCENTRATIONS IN THE WESTERN YUNCHENG BASIN, NORTH CHINA
M. CURRELL School of Geosciences, Monash University, Victoria 3800, Australia
Groundwater with high fluoride (F") concentrations (> 1.5 mg/L) occurs in shallow (< 50 m) and deep (> 150 m) wells from a Quaternary aquifer in the western Yuncheng basin, north China. The 500 m-thick aquifer consists of aeolian loess deposits, interlayered with fluvial and lacustrine sediments, and is the major water supply for drinking and irrigation in the region. Consumption of high F water has led to large outbreaks of dental and skeletal fluorosis in residents of the area, and many supply wells have been abandoned for this reason in the last 5 years. Major ion compositions and environmental isotopes were examined in this groundwater, in order to characterise the processes leading to fluoride enrichment, and the geochemical evolution of high F groundwater. and values indicate that groundwater with high F concentrations was recharged over a range of time periods, in a variety of climatic settings. F enrichment is thus thought to result from broad-scale
groundwater-aquifer matrix interactions after recharge, rather than recent surface processes (e.g. heavy evapotranspiration, anthropogenic pollution). High F groundwater possesses distinctive alkaline geochemistry, with high HCO3 and Na contents, along with low Ca content. This groundwater also has enriched values, indicating extensive dissolution of carbonate minerals at some stage during geochemical evolution. A fluoride enrichment mechanism is proposed, involving dissolution of carbonate in the aquifer matrix, followed by ion exchange between Ca^"" and Na"", interaction with fluorite (CaF2), plus or minus calcite precipitation. Low Ca content is crucial to this mechanism, due to its kinetic control on the normally slow, rate-limiting fluorite dissolution reaction. This mechanism may explain the wide occurrence of high F groundwater in conjunction with alkaline geochemistry, in a variety of aquifer environments around the world.
Keywords: fluoride, groundwater, isotopes, geochemistry, China Email: matthew.currell@sci.monash.edu.au
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
INLAND ACID SULPHATE SOILS: A STUDY OF THREE WETLANDS ALONG THE MURRAY RIVER FLOODPLAIN
F. GLOVER Department of Environmental Geoscience, La Trobe University, Victoria 3086, Australia
Acid sulphate soils (ASS) have become a topical issue in inland Australia since they have been recognised to occur along the Murray River. These soils contain sulphidic material which, when exposed to oxygen via drainage or disturbance, can then oxidise to form sulphuric acid. This can lead to environmental problems, including the mobilisation of heavy metals. The sulphidic material is formed by the reduction of sulphate (S04^"). which has been associated with dryland salinity. Wetlands along the Murray River provide an ideal environment for the production of sulphide minerals when they become waterlogged with saline water. The build up of sulphidic material has been further increased by the removal of natural wetting and drying cycles of the wetlands due to the changed hydrology of the Murray River. To investigate the problem of ASS in inland
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wetlands and determine the properties that allow recognition of high risk wetlands, three wetlands were chosen for this study; Bottle Bend Lagoon, Psyche Bend Lagoon and Tareena Billabong. Bottle Bend Lagoon had already undergone acidification prior to sampling. Monosulphide minerals, such as mackinawite (FegSs), are more common in these wetlands than pyrite (FeS2), because of the relatively short period since waterlogging has occurred. All three wetlands had a similar acid generating capacity, but carbonate minerals, such as aragonite (CaCOs), were only found in Psyche Bend Lagoon, where they are in excess of the acid generating capacity. The lack of carbonate minerals in Bottle Bend was thought to be one of the main reasons for acidification. However, the lack of acidification at Tareena Billabong, despite the presence of sulphides, is still unexplained.
Keywords: acid sulphate soils, wetlands, oxidation, acidification Email: fsglover@gmail.com
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
THE HYDROGEOLOGY OF THE UPPER CAMPASPE DEEP LEAD, NORTH CENTRAL VICTORIA
S. HONICKE Department of Environmental Geoscience, La Trobe University, Victoria 3086, Australia
Interest in the development of aquifers as a groundwater resource has increased as a result of the current drought, particularly for private and agricultural use in the rural areas of Victoria. One of these areas of interest is the Upper Campaspe Deep Lead, located approximately 26 km east-northeast of Bendigo. However, relatively little is known about the hydrogeology of this part of the aquifer, and the risk of overdevelopment, and thus unsustainable use, of this potential groundwater resource is high. The thickness of the Campaspe Deep Lead is variable along its length, ranging from approximately 10 m thick to approximately 40 m thick. This variability is most likely due to faulting creating accommodation space for extra sediment deposition.
Areas of recharge and the extent of interactions between surrounding aquifers and surface water courses have been investigated under hydrogeological and hydrochemical parameters. An increase in the thickness of the aquifer of approximately 15 m occurs in the same area as a change in the chemical composition of the groundwater, with the ratios of CI' to K"", Ca^"" and Mg^"" decreasing by up to a factor of one hundred. This suggests recharge into the deep lead, indirectly from the Campaspe River through the intermediate Newer Volcanics Basalt. The increase in thickness of the deep lead in this area has most likely been facilitated by an east-northeast trending fault.
Keywords: Campaspe Deep Lead, faulting, groundwater interactions, hydrology, hydrogeochemistry, surface water - groundwater interactions Email: sshonicke@students.latrobe.edu.au
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
MODELLING OF GROUNDWATER RECHARGE ON A SMALL SCALE (PADDOCK) USING MIKE SHE
J. p. S H A R P L E S Department of Environmental Geoscience, La Trobe University, Victoria 3086, Australia
This study makes use of the MIKE SHE modelling program to highlight the hydrological parameters affecting groundwater recharge on a small scale area near Willaura in western Victoria. The observation area was a paddock, 400 m by 800 m, with a subdued topography rising from north to south by 6 m. There is a natural drainage line which curves from the southwest to the northwest corner of the paddock. The drainage line is quite shallow; from the centre of the drainage line to the surrounding paddock there is only a 0.5 m elevation difference. Twelve piezometers with loggers were installed across the paddock and the groundwater level was recorded from April 2006 to March 2007. Over this time period the paddock was effectively unvegetated due to drought. Despite the minor topographical change across the paddock the pattern of groundwater recharge was quite varied. There were two large rainfall events during the observation period, one in July 2006 and one in January 2007. During the rainfall event in July 2006, 22 mm was recorded over 3 days. This produced significant recharge under the
drainage line, however no recharge was seen in the surrounding flatter areas of the paddock. In the larger January event, where 41 mm was recorded over 3 days, only minor recharge was seen in any of the piezometers. The recharge observed in the drainage line after the July event was attributed to overland flow (runoff) from the sloped sides accumulating and infiltrating in the centre of the drainage line. The lack of recharge after the January event demonstrates that evaporation is a key variable affecting recharge. Pan evaporation in January was four times higher than in July. Using MIKE SHE a model of the paddock was created. The model varified that the pattern of recharge under the drainage line is due to overland flow from the sloped sides. The model also demonstrates that the recharge pattern is very sensitive to the infiltration rate (hydraulic conductivity). The model however failed to replicate the observed effects of evaporation in the system. This highlights a shortcoming in the ability of MIKE SHE to correctly model evaporation in very low vegetation areas.
Keywords: hydrological modelling, groundwater recharge, MIKE SHE
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Email: jpsharples@students.latrobe.edu.au
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
THE HYDROGEOLOGY OF THE LAKE CONNEWARRE COMPLEX T, A. KEOGH School of Science and Engineering, University of Ballarat, Mt Helen, Victoria 3350, Australia This research project is investigating the hydrogeology of the Geelong Lake Connewarre salinity target area of the Corangamite Catchment Management Authority (CCMA). The project has application to salinity management; river, lake and wetland management; and strategic urban planning.
The main research objective is to provide a greater understanding of the interactions between the groundwater flow systems and surface water systems (fluvial, paludal, lacustrine, estuarine and marine) of the Geelong - Lake Connewarre salinity target area. To support this objective, the main research questions being investigated are:
The Lake Connewarre Complex lies to the southeast of the regional city of Geelong in Victoria, Australia and consists broadly of Lake Connewarre, Reedy Lake, Hospital and Salt swamps and associated sections of the lower Barwon River. It is one of 12 identified salinity target areas of the CCMA within south western Victoria and forms part of the Port Phillip Bay (Western Shoreline) and Bellarine Peninsula Ramsar Site protected by the Environment Protection and Biodiversity Conservation Act 1999.
• What are the groundwater systems in the Geelong - Lake Connewarre area?
There is no known information on the salinity processes, trends or actual risk to assets in the Geelong - Lake Connewarre target area. In comparison to many other lakes in the Corangamite region, the hydrogeology of the Lake Connewarre Complex is poorly understood, since there has been little research and investigation undertaken to date.
• What are the fluxes between the groundwater, surface water and marine systems? • How does the groundwater respond to changes in seawater and surface water levels? • How might the groundwater and surface water systems in the Geelong - Lake Connewarre area be characterised and classified? Answers to these questions will be achieved by delineating aquifers and quantifying their parameters and by using quantitative time series data and groundwater chemistry.
Keywords: hydrogeology. Lake Connewarre Complex, groundwater surface water interaction, salinity management Email: keogh.t@gmail.com
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I I
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
Theme 2
Economic and Mine Geology
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
DETERMINING PORPHYRY COPPER PROSPECTIVITY IN A NORTH AMERICAN MINING DISTRICT BY INTEGRATING GEOLOGICAL AND REMOTELY SENSED DATA INTO WEIGHTS-OF-EVIDENCE AND FUZZY LOGIC MODELS M. D. LINDSAY School of Geosciences, Monash University, Victoria 3800, Australia Two prospectivity mapping methods are applied to a 32,000 km^ study area within a North American porphyry copper district. Comparison of weights-of-evidence and fuzzy logic models are made based on the ability to identify new and existing areas of high prospectivity. Several layers of geological evidence are integrated into each model, including solid geology, regional faults, aeromagnetic and gravity surveys, geochemical anomalies, Landsat data and copper occurrence locations. Each model has been prepared, processed and evaluated using Spatial Analyst, Arc Spatial Data
Modeller and native tools within the ArcGIS computer application. Sensitivity analyses, such as conditional independence tests and random sampling, have been conducted to ensure the applicability of each data set in determining areas of high prospectivity. Each model has produced a map highlighting important known porphyry copper deposits and some new areas of interest. Statistical analysis of each model has revealed that fuzzy logic performs as well as or better than weights-of-evidence, but requires less computing power, input data and allows expert input from the operator.
Keywords: weights-of-evidence, fuzzy logic, mineral exploration, statistical analysis, convergent modeling, porphyry copper deposits, GIS, prospectivity mapping Email: mark.lindsay@sci.monash.edu.au
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Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
REMEDIATION OF MINE DISCHARGE WATER AT THE GLEN WILLS HISTORIC MINING REGION
A. J. N E L S 0 N \ J. A. Webb^ & D. Arne^ ^Department of Environmental Geoscience, La Trobe University, Victoria 3086, Australia ^Mt Wills Gold Mines NL, c/o Omeo Post Office, Victoria 3898, Australia
Arsenic-disseminated sulphide minerals are a common gangue phase associated within the mineralised zone of gold deposits at the Maude Mine in the Glen Wills historic mining region located in the highlands of north-eastern Victoria. Consequently, mine drainage in the underground workings is characterised by concentrations of arsenic upwards of 1800 ppb. Before ore extraction can recommence, the historical workings must be dewatered, with a view to disposing of the contaminated mine water into the adjacent Glen Wills Creek. In Victoria, any wastewater release into natural waterways must first comply with the EPA State Environmental Protection Policy for water quality. Arsenic concentrations must not exceed the ANZECC guideline boundary of
13 ppb. Hence, in order to comply with these guidelines the wastewater from the dewatering program must be remediated prior to disposal. To determine the most practical and cost effective method of remediation, a number of bench scale trials have been performed, testing commercial products which utilise the coagulation and adsorption methods of arsenic removal: ferric chloride, aluminium sulphate, polyaluminium chloride and granular ferric hydroxide. The arsenic removal efficiency and practical implementation of each method will be assessed, in order to choose the best remediation method for the water treatment program at the Glen Wills site.
Keywords: mine discharge, dewatering, arsenic contamination, remediation, coagulation, adsorption Email: aj2nelson@students.latrobe.edu.au
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
DISTRIBUTION AND MOBILITY POTENTIAL OF ARSENIC IN SOIL PROFILES IN PROXIMITY TO AN ABANDONED GOLD MINE, VICTORIA, AUSTRALIA
A. RAHMAN, K. Dowling & F, Zohora School of Science and Engineering, University of Ballarat, Mt Helen, Victoria 3350, Australia
Arsenic distribution and chemical fractionation has been studied in five soil profiles near an abandoned gold mining area in Clunes (Victoria, Australia). Total arsenic content was higher than recommended for the land use type, reaching a maximum value 1190 ppm. In general, total arsenic concentration decreased with depth in the profile. Sequential extraction was used to determine arsenic bonding relationship, specifically to assess the non-superficially bound-As, specifically bound-As, amorphous and poorly crystalline hydrous oxides of Fe and Al bound-As, well crystallised hydrous oxides of Fe and Al bound As and residual As. In soils with less than 50 ppm arsenic, bonding distribution was in the order: residual > well crystallised hydrous oxides of Fe and Al > amorphous and poorly crystalline hydrous oxides of Fe and Al > specifically sorbed As > non-specifically sorbed. In highly contamin-
ated soil, the order was amorphous and poorly crystalline hydrous oxides of Fe and Al > residual > well crystallised hydrous oxides of Fe and Al > specifically sorbed As > nonspecifically sorbed. Very little As was associated with non-specifically adsorbed phase which did not exceed 2% of total As, consistent with a lower risk of As leaching to the groundwater and limited bioavailability to plants and micro-organisms. The contribution of specifically bounded As varied from 2% to 19% indicating that As was potentially mobile in these soils. A greater proportion of As was associated in the amorphous Fe and Al phase (16-55% of the total As) than crystalline Fe and Al phase (11-36% of the total As). Arsenic mobilisation is possible at extremely high or low pH, and this may be particularly of importance to one of the profile samples (pH > 8), which was highly alkaline.
Keywords: soil, arsenic fractionation, sequential extractions, mining Email: kakon123@gmail.com
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I Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
THE MOBILITY OF TITANIUM IN HYDROTHERMAL SYSTEMS IN THE MOUNT ISA INLIER, NORTHWEST QUEENSLAND
V, Dl FLORIO School of Geosciences, Monash University, Victoria 3800, Australia inclusion analysis, whole rock XRF analysis, examination of radiometric survey data and thin section petrography have been used to analyse these hydrothermal systems.
The Mount Isa Inlier is located in northwest Queensland, Australia, and belongs to the Northern Australian Precambrian Craton. Due to an intense tectonic evolution, the Mount Isa region holds hosts to a variety of hydrothermal ore deposits, including uranium, copper and gold. Some of these deposits formed within unusual hydrothermal systems, in particular an interesting association between U, Ti, Zr and REE, most of which are generally considered to be immobile elements. These unusual deposits have provided researchers with difficulties in determining the source of the mineralising fluids and the genesis of the deposits. This study focuses on understanding processes responsible for mobilising the immobile elements, particularly titanium, in a mid-crustal metamorphic belt.
In the Mt Isa Inlier titanium is associated with uranium deposits, commonly as the uranium mineral brannerite ((U, Ca, Ce)(Ti, Fe)206), but also in peripheral Ti-rich, low-U mineralised systems, as ilmenite (FeTiOs) and titanite (CaTiSiOs). A number of uranium prospects and mines are located in close proximity to where titanium-bearing samples were collected in this study. These uranium prospects and hydrothermal titanium occurrences cluster in the vicinity of radiometrically hot granitic intrusions. Thin section and electron microprobe analysis has found that Ti-rich mineralisation is associated with fluorapatite-enriched alteration (apatite contains up 3.744% F), suggesting an association with F" and P04^" in hydrothermal fluids. These anions can be found in either metamorphic or magmatic fluids, but tend to be more concentrated in fluids sourced from highly fractionated magmas.
As an immobile element, titanium is frequently used as a diagnostic tool to determine the mobility of other elements in hydrothermal alteration systems. However, recent research has found that titanium complexes with fluorine as an aqueous species and thus may be highly mobile in specific settings. Therefore, the results of this study will not only have implications for understanding the genesis of mid-crustal uranium deposits, but also for all studies that use Ti as an immobile element to investigate mobility of other elements.
In combination, the observation that U-TiZr-REE mineralisation clusters around radiometrically hot granitic intrusions, the fact that these are incompatible elements enriched through granitic fractionation, and the interpretation of F" and P04^" in hydrothermal fluids, suggest that genesis of these deposits involved a granitic source. Mixing with metamorphic fluids is yet to be investigated by fluid inclusion analysis.
This study has focused on magmatic and metamorphic sources as the two possible hydrothermal systems that formed the U-TiZr-REE mineralised systems Analytical techniques such as microprobe analysis, fluid
Keywords: Mount Isa Inlier, titanium, hydrothermal system, magmatic, metamorphic
11
I Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
"^"AR/^^AR DATING AND FLUID NOBLE GAS CONSTRAINTS ON OROGENIC GOLD MINERALISATION IN VICTORIA, AUSTRALIA A. FAIRMAID, D. Phillips, M. Kendrick & B, Fu School of Earth Sciences, University of Melbourne, Victoria 3010, Australia
spectrometry of irradiated quartz samples (extended Ar-Ar methodology). Ar and Br/CIl/CI are powerful tools for determining the origin and interaction of fluids as both groups of elements behave conservatively in the Earth's crust. Halogens can unravel processes such as the acquisition of salinity, whilst noble gas isotope ratios vary by orders of magnitude, making minor contributions from different fluid reservoirs or fluid mixing easy to identify.
The Ballarat East (408 t) and Maldon gold deposits (56 t) in the (c. 0.4 Ga) western Lachlan Fold Belt of Victoria, represent turbidite-hosted orogenic gold deposits. The Maldon deposit differs from the Ballarat East deposit as it has a contact metamorphic overprint due to its proximity to the Harcourt Granite. The existing "^^Ar/^^Ar geochronological database for Victoria is extensive. However, the wide range of ages (455-370 Ma) for Ballarat East could reflect multiple deformation events and/or the effect of detrital ages, and some of these ages may be unrelated to gold mineralisation. Preliminary sericite ages (418 ± 3 Ma and 376 ± 4 Ma) suggest multiple stages of hydrothermal alteration. The youngest mica ages of -Z12 Ma, determined for the Maldon deposit, could reflect growth during granite emplacement or resetting during contact metamorphism.
Gold-bearing quartz veins from both deposits contain low salinity H2O-CO2 fluid inclusions. "^^Ar/^^Ar values from fluid inclusions are close to ASW, suggesting that the noble gases are derived from the atmosphere/hydrosphere, as opposed to a mantle/magmatic source. Thus, sedimentary formation waters appear to be a dominant fluid component in both deposits. The "^^Ar/^^Ar values could also represent a metamorphic fluid that has acquired low "^^Ar/^^Ar values. Br/CI and l/CI values are typical of sedimentary formation waters.
The fluid inclusion noble gas (Ar, Kr and Xe) and the halogen (CI, Br and I) isotopic compositions can be determined simultaneously by noble gas mass
Keywords: "^^Ar/^^Ar dating, noble gases, orogenic gold Email: a.fairmaid2@pgrad.unimelb.edu.au
12
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
THE OCCURRENCE OF PYROMETAMORPHIC ROCK IN THE DAWSON COAL MINE, CENTRAL QUEENSLAND
p. W. HOILES\ P. W. Whitehead^ & B. G. Lottermoser^ ^School of Earth Sciences, University of Melbourne, Victoria 3010, Australia ^School of Earth and Environmental Sciences, James Cook University, PO Box 6811, Cairns, Queensland 4870, Australia ^School of Earth and Environmental Sciences, James Cook University, Townsville, Queensland 4811, Australia
resultant colour change one of dehydration and oxidation.
Coal seam fires have thermally altered surrounding country rock to produce pyrometamorphic rock at a series of locations in the Dawson Central Coal Mine, located near Moura in Central Queensland, Australia.
The paralavas are highly heterogeneous rocks that vary markedly in colour and structure. They are commonly holohyaline and are highly vesicular. Evidence of both ductile and brittle processes is apparent, with many paralavas showing evidence of viscous flow, with typical flow structures developed, while others show substantial brecciation. Paralavas represent the melted rock located adjacent to the burning centre of the coal seam fire, lining various chimney structures where hot gases from the fire have exhausted and melted the rock. Paralavas often include blocks of coal, unmelted clinker and clinker that show signs of incipient melting.
The pyrometamorphic rock can be divided into two major groups of 'clinker' and 'paralava'. Clinker has undergone thermal alteration without melting, whereas paralava is the product of either partial or complete melting. Two main types of clinker are recognised with a gradational boundary between them. A pink fades, which represents the highest degree of thermal alteration of the clinkers, exists proximally to the coal seam fire, and grades into a yellow clinker fades. The yellow clinker fades grades into unaltered country rock moving away from the coal seam fire. The country rock, a volcaniclastic sandstone, is thermally altered to become clinker via conduction through the rock surrounding the coal seam fire, with the
Active 'hot holes' exist at the Dawson Central Coal Mine which are exhausting hot gases and steam that smell of hydrocarbons and burning coal, indicating that coal seam fires are still present within the mine.
Keywords: pyrometamorphic, clinker, paralava, Moura Email: p.hoiles@pgrad.unimelb.edu.au
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Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
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I
14
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
Theme 3
Geothermal Systems
15
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
HEAT FLOW DATA IN THE MURRAY BASIN, SOUTH AUSTRALIA: RELATIONSHIP OF HIGH HEAT ZONES TO GEOLOGICAL EVENTS AND GRANITIC INLIERS
L. CRISTANELLI School of Geosciences, Monash University, Victoria 3800, Australia
be taken into consideration. Heat flow within this area was calculated by using thermal gradients and temperatures logs recovered by water bores using a thermistor logging tool. The conductivity was measured using published values from a study conducted in the adjacent basin (Otway Basin). A 1 dimensional model for each borehole was then constructed to achieve higher accuracy within the heat flow models.
To determine crustal heat flow both thermal gradient and thermal conductivity are required. These two measurements are combined to obtain heat flow combining the temperature and the thermal conductivity of a particular rock type. Within this project, a total of 13 boreholes have been measured within a section of the Murray Basin, South Australia, to achieve an overall heat flow of the area. The selected section of the Murray Basin falls within the SAHFA (South Australia heat flow anomaly), thus increasing the potential of high heat flow zones.
Considerations and comparison of high heat flow zones to both geology and gravity maps showed that granitic sources formed by the Delamerian Orogeny within the Mount Lofty Ranges, could be the possible sources of heat. This study concentrates on the potential heat flow within a section of the Murray Basin where no previous work has previously been done, and potentially translate into a potential geothermal prospect.
Heat flow and geothermal potential is best achieved with a solid understanding of the regional geology. Thus, to better understand the heat flow and potential heat sources areas within this region, the geology of the Murray Basin and near by Mount Lofty Ranges had to
16
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
HEAT FLOW IN THE LATROBE VALLEY: THE ROLE OF THERMAL CONDUCTIVITY AND HEAT REFRACTION
S. WRIGHT, B. Harrison & M. Sandiford School of Earth Sciences, University of Melbourne, Victoria 3010, Australia
The demand for sustainable energy resources continues to increase with rising awareness of the global impact of climate change, and as a consequence, exploration for untapped geothermal energy resources is rapidly increasing. Exploration for potential geothermal resources requires not only knowledge of global and regional heat flow mechanisms, but also an understanding of how surface heat flow measurements correlate with the distribution of temperature at depth. This correlation is particularly important in regimes with significant conductivity contrasts, where heat refraction can be substantial.
sequences in the Latrobe Valley is modelled to show how heat refraction affects observed surface heat flow values. It is suggested that the highest subsurface temperatures may not correspond with the highest surface heat flow anomalies. A thick folded insulator may actually result in a negative heat flow anomaly overlying a region of higher than average crustal temperatures. The modelled heat refraction that occurs due to insulating layers is also used to test alternative modelling techniques that rely on shallow bore hole temperature measurements which may not accurately reflect deeper conductive heat flow.
In the Latrobe Valley, heat refraction is thought to occur primarily as a result of the abrupt change in thermal conductivity across lithological boundaries. This study investigates how buried insulators affect the temperature gradient and heat flow within a given region. In particular, how lateral heat flow is controlled by heat refraction due to insulating layers. The thermal conductivity distribution of coal
By comparing the modelled subsurface and observed surface heat flow in the Latrobe Valley there is the potential to improve the understanding of the factors that control surface heat flow and thus expand the number of existing geothermal exploration targets to include both high and low heat flow anomalies.
Keywords: thermal conductivity, heat refraction, heat flow, Latrobe Valley Email: s.wright@ugrad.unimelb.edu.au
17
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne. September 2008
18
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
Theme 4
Vertebrate Palaeontology
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Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
A BASAL ACTINOPTERYGIAN FISH FROM THE MIDDLE DEVONIAN AZTEC SILTSTONE OF ANTARCTICA
B, CHOO Museum Victoria, PO Box 666, Melbourne, Victoria 3001, Australia Research School of Earth Sciences, The Australian National University, ACT 0200, Australia
with anterior flexure, porous ornamentation on the clavicle, an elongate body form with macromeric squamation and anterior pectoral lepidotrichia which are unsegmented for much of their length. A phylogenetic analysis based on dermal skeletal features indicates that Donnrosenia is the sister taxon to Howqualepis from the Middle Devonian of Victoria, Australia, and reinforces the already strong biogeographical similarities between the Middle Devonian ichthyofaunas of southeastern Australia and Antarctica.
In contrast to their huge extant diversity, Devonian actinopterygians or ray-finned fishes are known from relatively few genera. A basal actinopterygian fish, Donnrosenia schaefferi, was recently described from the Middle Devonian (Givetian) Aztec Siltstone of southern Victoria Land, Antarctica. This represents the earliest record of an articulated actinopterygian from that continent. Donnrosenia is characterised by the large parietals which are of almost equivalent size to the frontals, very small intertemporals, a small accessory operculum, a deep dentary
Keywords: fossil fish, Actinopterygii, Antarctica, Devonian, Donnrosenia,
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Howqualepididae
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
A NEW GENUS OF LUNGFISH FROM THE LATE DEVONIAN (FRASNIAN) OF WESTERN AUSTRALIA A. M. CLEMENT Museum Victoria, PO Box 666, Melbourne, Victoria 3001, Australia Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 0200, Australia The Gogo Formation of north Western Australia has historically yielded many specimens from a diverse range of Devonian taxa. Many of which are exceptionally preserved, allowing us to gather detailed anatomical information about the fish of the ancient Gogo ecosystem. A new holodontid lungfish Xeradipterus hatcheri gen et sp. nov. is described from the Late Devonian (Frasnian) Gogo Formation. The material comprises a single specimen preserved in a large concretion, represented by elements of
the skull roof, cheek, lower jaw, palate, shoulder girdle and parts of the postcranial skeleton. Xeradipterus gen. nov. differs from other holodontids by its broad crushing dentition, prearticular tooth-plates, lack of prominent teeth and ordered tooth rows, and in its parasphenoid morphology. Results of PAUP analysis for 32 dipnoan taxa revealed that the new genus is the plesiomorphic sistertaxon to all other Gogo holodontids, suggesting a possible endemic radiation of holodontids within the Gogo fauna.
Keywords: Devonian, Dipnoi, phylogeny, Gogo Formation Email: aclement@museum.vic.gov.au
21
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
HIGH RESOLUTION CT-TOMOGRAPHY OF FOSSILS: THE BRAINCASE OF GOGONASUS ANDREWSAE (SARCOPTERYGII, TETRAPODOMORPHA)
T. HOLLAND School of Geosciences, Monash University, Victoria 3800, Australia Museum Victoria, PO Box 666, Melbourne, Victoria 3001, Australia
high resolution CT-tomography may resolve this phylogenetic position, as well as illuminate current understandings of endocranial character distribution throughout tetrapodomorph fish and early tetrapods. Initial research into the internal braincase morphology in tetrapodomorph fish involved Sollas's grinding technique, which ultimately destroyed the material under study, whereas CT-scanning facilities and software developed at The Australian National University allows resolution of up to 2-3 microns and up to 120 times magnification. New information pertaining to the olfactory capsule, the internal division separating the ethmoid and sphenoid division of the ethmosphenoid and the internal cranial cavity are presented for the first time.
First described from incomplete material in 1985, Gogonasus andrewsae was initially placed near the base of the 'Osteolepiformes', now thought to be paraphyletic grade of tetrapodomorph fish. Since that time, numerous specimens have been found from the Frasnian Gogo Formation of Gogo, Western Australia, including the first complete individual in 2005. Cladistical analysis incorporating previously unknown data regarding the spiracular chamber and pectoral fin resulted in a more crownward position of Gogonasus amongst the Tetrapodomorpha, as the sister taxon to 'Elpistostegalia' + Tetrapoda. This phylogeny has since been refuted by several authors in favour of a more basal placement. New data on the internal braincase morphology of Gogonasus using
Keywords: Gogonasus, braincase, tomography, Tetrapodomorpha, Devonian, Gogo Email: tholland@museum.vic.gov.au
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Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
AUSTRALIAN CRAWL: EVIDENCE FOR THE FISH/TETRAPOD TRANSITION IN AUSTRALIA
T. HOLLAND School of Geosciences, Monash University, Victoria 3800, Australia Museum Victoria, PO Box 666, Melbourne, Victoria 3001, Australia The evolution of land-dwelling tetrapods from water-based tetrapodomorph fish is one of the most heralded research areas in vertebrate palaetonotlogy. Centred on much of this study are the 'elpistostegalid' fishes, known predominately from the uppermost Middle-Late Devonian of the Northern Hemisphere. This tetrapodomorph grade is regarding as exhibiting intermediate features between fish/tetrapods, with most authors believing this transition to have occurred in Euramerica. The description of a new articulated tetrapodomorph fish Howittichthys warrenae from the Givetian-Frasnain site of Mt Howitt, Victoria, is significant in displaying several features present in 'elpistostegalids'. Such morphology includes the presence of rhombic scales bearing open reticulate ornamentation, a relatively long pectoral fin lobe and elongate, unbroken lepidiotrichia.
However, the partially complete nature of the specimen impedes firm taxonomic assignment, with the alternative hypothesis being that the taxa represents a more basal tetrapodomorph similar to Glyptopomus or Liptotychius. This new discovery of a possible 'elpistostegalid' from Mt Howitt, as well as the oldest tetrapod-trackways in the world (Frasnian) along the Genoa River, Victoria and the presence of the Late Frasnian tetrapod Metaxygnathus near Forbes, NSW lends support for an East Gondwana origin for the clade containing 'Elpistostegalia' + Tetrapoda. Such an origin and dispersal of fauna to the Northern Hemisphere would bolster evidence of a migratory event between Gondwana-Euramerica at the end of the Givetian.
Keywords: Howittichthys, Tetrapodomorpha, Devonian, Mt. Howitt, Genoa River trackways Email: tholland@museum.vic.gov.au
23
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne. September 2008
24
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
Theme 5
Climate
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Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
AN IMPROVED AND UPDATED CLIMATOLOGY OF EXPLOSIVE CYCLOGENESIS
J. ALLEN School of Earth Sciences, University of Melbourne, Victoria 3010, Australia
SH to isolate the most significant systems, both in deepening rate and genesis location. An updated bomb climatology has been constructed using the Melbourne University Tracking scheme with the latest NCEP2 and JRA reanalyses. Using this, an examination was undertaken of the decadal and annual trends in explosive cyclone numbers for the SH noting an apparent increase since the mid1990s. The effects of planetary and synoptic scale modes of variability on the system development have also been investigated.
Rapid extratropical cyclogenesis events (referred to as 'bombs') are difficult to predict and give rise to extreme meteorological and oceanic conditions. While much research into their structure and formation has been completed in the Northern Hemisphere (NH), less investigation has been undertaken in the Southern Hemisphere (SH). Detailed climatologies of bomb events are few in number, and prior to this study have not used the latest reanalysis data. A modern definition for an explosive event was defined by Sanders and Gyakum (1980) as a 24 hPa drop in central pressure in 24 hours relative to latitude (referred to as 1 Bergeron). However, this definition may be less relevant for the SH given the strong climatological pressure gradient at mid to high latitudes. This study attempts to clarify the use of this bomb definition as it is applied to the
In addition, two separate case studies occurring in March of 2007 and 2008 have been analysed using high resolution data from the Limited Area Prediction System (LAPS, 35 km horizontal, 29 vertical levels) at the Bureau of Meteorology to ascertain whether SH bombs rely on the same large scale formative characteristics as NH systems.
Keywords: cyclogenesis, bombs, modes of variability Email: j.allen2@ugrad.unimelb.edu.au
26
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
AUSTRALIAN EASTERLY DIPS
D, SGARB0SSA\ M. Reeder\ R. Wardle^ & J. Kepert^ ^School of Mathematical Sciences, Monash University, Victoria 3800, Australia. ^Centre for Australian Weather and Climate Research, Bureau of Meteorology, GPO Box 1289, Melbourne, Victoria 3001, Australia
During summer over the easternmost part of Australia, the low-level isobars often dip sharply poleward. These troughs, along with the associated deflection of the onshore easterly flow, are commonly called easterly dips. At times easterly dips extend meridionally the length of the continent. They are commonly the sites for deep convection, one recent example being 27 February 2007, a day on which destructive storms battered Canberra. While Australian easterly dips are common and appear to be implicated in the development of severe weather, they have received relatively little attention; greater emphasis has been placed on the closely related troughs that form along the western Australian seaboard.
Bureau of Meteorology Mesoscale Assimilation Limited Area Prediction System. The main results are that: (i) at night the ageostrophic flow associated with the trough accelerates strongly and the trough sharpens markedly; (ii) at night a pronounced line of cyclonic vorticity develops along the trough axis; (iii) like heat lows, easterly dips are shallow with low-level convergence into the trough replaced by divergence above 700 hPa; and (iv) a dryline lies along the trough, separating dry continental air to the west from moist maritime air to the east. In addition, a 20-year climatology of easterly dips is constructed from the NCEP/DOE reanalysis 2 dataset, the results of which will be discussed.
The structure and evolution of four easterly dips is investigated using the Australian
Keywords: Australia, heat troughs, easterly wind, dryline, ageostrophic circulation, summer, diurnal variations, climatology, case studies Email: dean.sgarbossa@sci.monash.edu.au
27
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
REDUCING THE UNCERTAINTY IN AR4 RAINFALL PROJECTIONS FOR THE MURRAY-DARLING BASIN E. CHANDLER School of Earth Sciences, University of Melbourne, Victoria 3010, Australia This study investigates the performance of the current IPCC fourth assessment report (AR4) Global Climate Models (GCMs) in simulating Australian rainfall under the A1B scenario and evaluates each model on their ability to reproduce the present day climate. This evaluation involves model simulation of observed mean rainfall, spatial variability, the observed seasonal cycle and interannual variability.
The Murray-Darling Basin in eastern Australia is by far the most significant agricultural region in the country. While the Basin receives only 6% of Australia's annual rainfall, it contains over 70% of irrigation resources and 42% of the nation's farmland. Research trends and climate model simulations suggest some of Australia's rainfall patterns may be changing in response to a wide range of natural and anthropogenic forcings, and this leads to an increased vulnerability on water resources in the Basin. While better estimates of these trends are important in determining potential water stresses on the Basin into the future, predictions of rainfall for the century are characterised by a high level of uncertainty.
The results of this study show a reduced uncertainty in rainfall projections to the end of the century for the Murray-Darling Basin region.
Keywords: rainfall, Murray-Darling Basin, climate Email: e.chandler@pgrad.unimelb.edu.au
28
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
Theme 6
Earth Dynamics & Chemistry
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Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
DEFORMATION OF A SUBDUCTING SLAB: THE VARIABLE BOUNDARY CONDITIONS OF A SLAB TEAR
K. S. ELY & M. Sandiford School of Earth Sciences, University of Melbourne, Victoria 3010, Australia
propagation at 200 km depth driven by slab pull forces. In contrast, the western boundary beneath the Savu Sea is defined by a record of more moderate seismic activity. The Savu Sea region is unusual in that many of the
The Neogene collision of the northern margin of the Australian continent with the Banda Arc provides an opportunity to investigate the early stages of arc-continental collision processes. The end of volcanism in the arc and subsequent uplift is attributed to the cessation of subduction, and the lack of intermediate depth earthquakes in this region supports the proposal that a slab tear underlies this segment of the arc. Investigation of the dynamics of this slab tear shows a strong asymmetry in the boundary conditions.
shallow earthquake events have subvertical
nodal planes, and focal mechanism solutions indicate the slab is under compression at intermediate depths. Average volcano spacing in the overlying arc is less than half that of the arc farther west suggesting an increased melt flux. High water flux can result in a state of a low viscosity overlying mantle wedge and evidence from the Savu Sea region is consistent with models that show a correlation with high level down-dip compression in the subducting slab and a low viscosity mantle wedge. The asymmetry of the Wetar slab tear is also attributed to the subduction of transitional continental crust beneath the Savu Sea, resulting in a relatively buoyant slab with potentially greater water content than the adjacent oceanic crust.
Earthquake catalogues are used to analyse the intensity and nature of deformation in the subducting slab and overlying lithosphere. In the Sunda-Banda arc a high degree of heterogeneity is revealed, and is related here to collision processes, and variation in the nature of the subducting materials. Intense, intermediate depth, extensional earthquake activity at the eastern boundary, near Romang, is consistent with tear
Keywords: Sunda-Banda arc, slab tear, earthquakes, focal mechanism solutions Email: kimberlite1@gmail.com
30
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
THE APPLICATION OF MICRO-ANALYTICAL TECHNIQUES IN UNDERSTANDING THE EVOLUTION OF LARGE SILICIC SYSTEMS: EVIDENCE FROM CERRO GALAN CALDERA, NORTHWEST ARGENTINA
C. FOLKES\ S. de Silva^ R. Cas\ H. Wright^ & J. Viramonte^ ^School of Geosciences, Monash University, Victoria 3800, Australia ^Department of Geosciences, Oregon State University, Corvallis, Oregon, USA ^Institute GEONORTE and CONICET, Universidad Nacional de Salta, Argentina
Large caldera-forming ignimbrite eruptions (> 1,000 km^ ejected material) have had a profound effect on the Earth's surface, atmosphere and biosphere throughout its history. Surprisingly, we know very little about the eruption dynamics and magma chamber evolution of these large 'supervolcanoes', because eruptions of this magnitude have never been witnessed or documented in human history. The Cerro Galan caldera in northwest Argentina is such an example of these large-scale volcanic centres and provides an excellent case study in understanding the long-term subsurface magma dynamics and eruptive evolution of these large calderas. New "^^Ar/^^Ar eruption ages and detailed fieldwork show that there have been at least seven large ignimbriteforming eruptions over a period of - 4 million years in the Galan eruptive centre. The eruptions became more voluminous with time, culminating in the eruption of the largest Cerro Galan ignimbrite, which extends up to 70 km in all directions away from the caldera.
The petrology and geochemistry of all the ignimbrite units associated with the Galan eruptive centre are remarkably similar; therefore a variety of new analytical techniques were used to investigate the geochemical evolution of the Galan system. Stable isotope ratios C^O/^^O) of quartz phenocrysts were analysed from all the eruptive units and remain remarkably constant over the 4 million year eruptive history (+ 8.89.6). Magmatic ages were calculated from UPb geochronology of zircon phenocrysts and the results show that zircon crystals from older eruptions (antecrysts) are present in each subsequent eruption. The combined geochemical and petrographic evidence presented here suggests a common, homogeneous magma source that fed these eruptions and was continuously 'tapped' over this time period with recycling of magmatic material. This has important implications for the longevity of such magma systems responsible for some of the world's largest explosive eruptions.
Keywords: central Andes, caldera, ignimbrite, oxygen isotopes, U-Pb geochronology Email: chris.folkes@sci.monash.edu.au
31
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
THE EROSION RATES OF THE DARLING ESCARPMENT, WESTERN AUSTRALIA
S. JAKICA School of Earth Sciences, University of Melbourne, Victoria 3010, Australia
The Darling Escarpment is one of the most prominent linear topographic escarpments of the Australian continent, yet it has been historically inactive in terms of earthquakes, which brings the question when and how did it originate? ''°Be cosmogenic analysis of the Darling Escarpment has been used to determine bedrock erosion rates along the escarpment and to quantitatively estimate the rate at which the scarp has retreated over the late Quaternary.
(3.57 ± 0.29 m/m.y. and 3.42 ± 0.28 m/m.y.) and Darling Escarpment range front (2.58 ± 0.22 m/m.y. and 5.47 ± 0.42 m/m.y.) erosion rates. Surprisingly, the erosion rates of the Darling Escarpment Serpentine Falls, located south of the Swan River are also very slow (4.03 ± 0.33 m/m.y. at the summit south of the falls, 3.27 ± 0.27 m/m.y. at the falls slope and 9.81 ± 0.68 m/m.y. at the base of the falls). These results of very slow and spatially equivocal erosion rates at summits, hillslopes and valleys within the Darling Escarpment provide evidence for a geomorphologically ancient, steady state landform.
Cosmogenic concentrations in the exposed bedrock surfaces along the Swan River, Serpentine and Whitby falls, and scarp summits and range fronts show very slow rates of erosion. Bedrock erosion rates of the Darling Escarpment summit surface (0.49 ± 0.07 m/m.y. and 3.27 ± 0.27 m/m.y.) are consistent with river incision rates
The results further show how cosmogenic analysis is a very useful tool in defining the seismic activity over a landscape over a half a million years time interval.
Keywords: cosmogenic isotopes, landscape evolution. Darling Escarpment Email: s.jakica@pgrad.unimelb.edu.au
32
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
THE STRUCTURAL HISTORY AND ARCHITECTURE OF THE COVERED ANTIFORMAL STACK, HEATHCOTE FAULT ZONE, VICTORIA
R. D. KOCH School of Geosciences, Monash University, Victoria 3800, Australia The Heathcote Fault Zone is located within the Lachlan Fold Belt and represents the eastern boundary of the Bendigo Zone. Recently collected deep crustal seismic data collected from across Victoria has revealed the Heathcote Fault Zone displays a strong listric geometry that continues down to approximately 20 km depth, or possibly even the Moho. Located in the northern segment of the Heathcote Fault Zone is a covered antiformal stack that can only be mapped using geophysical techniques.
then constructed using data collected from a high resolution ground magnetic survey from which a 3D model was created. This antiformal stack can be seen in map view. The limbs of the folds are not overturned and therefore may have formed in a strike-slip environment. There is no obvious buttress observed in the geophysics. The forward models (cross sections) through the stack show that the dip of the beds is very steep. This is consistent with what is seen in the deep crustal seismic sections.
The Heathcote Fault Zone was initially formed in the Benambran Orogen (430 Ma) and was then reactivated in the Tabberabberan Orogen (380 Ma). This reactivation of the Heathcote Fault Zone has occurred with dextral strike-slip movement as there are steeply plunging folds oblique to major bounding faults, which occur within the hanging wall. Mapping further south by suggests that late movement on the fault was dextral.
There are two possible scenarios for the formation of the antiformal stack. One possibility is the antiformal stack formed during late stage dextral reactivation along the Heathcote Fault Zone during the Tabberabberan Orogeny. The stack may have formed by high friction coefficients on the eastern side of the fault zone thus forcing the antiformal stack to form. The other possibility is that the northwest curve of the Heathcote Fault Zone above the antiformal stack acted as a buttress for its formation during thusting with a 90° rotation causing it to appear in map view.
By combining multiple geophysical methods such as gravity, magnetics and seismic, a 2D interpretation of the antiformal stack has been created. Forward models were
Keywords: antiformal stack, Heathcote Fault Zone, geophysics, Lachlan Fold Belt
33
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
THE DYNAMIC MULTI-PHASE ERUPTIVE PROCESSES AND ASSOCIATED DEPOSITS OF THE ARGYLE (AK1) LAMPROITE VOLCANIC SYSTEM, HALLS CREEK MOBILE ZONE, WESTERN AUSTRALIA
M. A, W. WILLCOCK School of Geosciences, Monash University, Victoria 3800, Australia
basaltic nature of the lamproite, however classification was limited by the high degree of alteration, mineral replacement and weathering associated with this type of in-vent volcaniclastic deposit.
There continues to be a need for a physical volcanological approach to understanding the facies and eruptive processes of the 1178 ±47 Ma Argyle lamproite volcanic system. This research focuses on developing further the description of the internal facies of the lamproite pipe and investigating the magmatic and eruptive processes of the system. Through the integration of graphic core logging techniques, thin section and geochemical analysis, the existence of two major facies within the diamondiferous lamproite were identified. The facies included firstly, the quartz xenocryst rich, clay to lapilli sized tuff (poorly sorted, massive to diffusely bedded with internal units) and secondly; the olivine crystal rich, clay-lapilli sized tuff (poorly sorted, massive, structureless). The lamproite rocks were found to be highly magnesian (MgO 5.1-24 wt %) and enriched in K2O (0.40-6.37 wt %), Ti02 (1.0-2.87 wt %), CaO (0.44-9.60 wt %), with high K2O/AI2O3 (average of 0.90 wt %), with low Na20 (< 0.21 wt %) abundances. These results are common to lamproite. Further geochemical comparisons illustrated the ultrabasic to basic
The nature of the deposits and associated processes of the Argyle volcanic system have led to the proposal of a multi-phase eruptive history with associated differing eruptive styles, deposit thickness and textural characteristics. The system was shown to have formed from a series of phreatomagmatic and magmatic eruptive events. The large amount of erupted material from these events was transported and deposited via dynamic pyroclastic flows which resulted from buoyant eruption collum collapse and base surges which produced localized bedded units preserved within the vent. This study has enabled the validation of previous work on the volcanology and geology of the Argyle lamproite system while increasing understanding of the major characteristics and processes of this world leading diamond deposit.
Keywords: lamproite, geochemistry, volcanology, facies
34
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
THE GEOCHEMISTRY OF THE WEST AUSTRALIAN, WEST KIMBERLEY PROVINCE LAMPROITES
R. CHESLER, J. Hergt, D. Phillips & R. Maas School of Earth Sciences, University of Melbourne, Victoria 3010, Australia The West Kimberley Province is located along the southwest margin of the Kimberley Block, Western Australia. Significant geochemical variation exists throughout the region, from olivine-rich, diamondiferous varieties, to leucite-rich, non-diamondiferous bodies. Bulk rock major and trace element compositions, as well as Sr-Nd-Hf isotopic compositions were measured with the aim of determining the intrinsic geochemical differences between leucite and olivine lamproites, as well as the processes leading to lamproite genesis in this region.
lamproites can be explained by the assimilation of continental crust into this 'common parent', followed (or accompanied by) fractional crystallisation. The olivine lamproites are best explained as variable mixtures between an ultramafic magma and the 'common parent'. The presence of diamonds in some of the olivine lamproites from this province requires the rapid rise of a deep-seated magma. We suggest that Group I kimberlites could provide the necessary endmember for the olivine lamproite suite.
The trace element and isotopic signatures preserved in the lamproites are inconsistent with the partial melting of a 'normal' depleted mantle peridotite source. Their distinctive Sr, Nd and Hf isotope signatures requires an enriched component which has undergone long term isolation from the convecting mantle asthenosphere.
Thus the lamproites from the West Kimberley Province represent small degree melts from an ancient, enriched subcontinental mantle lithosphere source. Those that have been swept into Group I kimberlite magma and carried to the surface rapidly are represented by the olivine lamproite suite, many of which preserve diamonds. In contrast, those that did not interact with kimberlite, or stalled and became fractionated and/or contaminated by continental crust (the leucite lamproites) are barren.
The convergence of olivine and leucite lamproite compositions in isotopic space implies a 'common parent' could be central to the generation of both suites. The leucite
Keywords: geochemistry, lamproite. West Kimberley Province, Nd-Sr-Hf isotopes Email: rchesler@unimelb.edu.au
35
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
THE AGE, GEOCHEMISTRY AND PETROGENESIS OF AN UNUSUAL ALKALINE INTRUSION IN THE WESTERN PILBARA CRATON, WESTERN AUSTRALIA
E. MATCHAN\ J. Hergt\ D. Phillips^ & S. Shee^ ^School of Earth Sciences, University of Melbourne, Victoria 3010, Australia ^De Beers Exploration Australia Ltd. (previous)
The recently discovered Yanyare dykes are located approximately 80 km south-southwest of Karratha in the northwestern Pilbara Craton. The approximately 5 km long Yanyare-02 dyke strikes north-northeast and intrudes intercalated sedimentary and volcanic units of the Palaeoproterozoic Fortescue Group. The dyke has an inequigranular texture and is comprised of intensely altered olivine macrocrysts set in a matrix of phlogopite (55%), sanidine (20%) and fluorapatite (15%).
similarities to both calc-alkaline lamprophyres and olivine lamproites, making classification difficult. On the basis of whole rock geochemistry, the notable absence of accessory minerals typical of lamproites, and phlogopite chemistry, the Yanyare-02 body would be classified as an olivine-phlogopitesanidine calc-alkaline lamprophyre. However, based on similarities in Hf-Nd isotope geochemistry, the preferred classification of the dyke is an olivine lamproite of the lamprophyre facies. A sub-continental lithospheric origin is proposed for Yanyare02, involving an ancient, subducted component of oceanic crust.
laser step-heating analyses of phlogopite grains produced a weighted mean age of 1724 ± 8 Ma. Rb-Sr analyses of whole rock and phlogopite separates yielded isochron ages of 1675 ± 10 Ma and 1689 ± 10 Ma. The former age is preferred, based on the reproducibility of results. The younger Rb-Sr ages are attributed to alteration-induced elevation of the initial Sr ratios.
No tectonic event is recognised at ca.1.7Ga in the Pilbara and the diamondiferous Nabberu kimberlites southeast of the craton are geologically constrained as -1900 Ma, with associated barren lamprophyres bracketed at 1900-1700 Ma. Yanyare-02 may therefore be part of a prolonged Palaeoproterozoic history of deepseated magmatism across the Pilbara, raising the potential for discovery of diamondiferous bodies in the west of the craton.
Average initial (1.72 Ga) ratios for Yanyare02 are: = 0.708; = 0.510; and '^W^^Hfi = 0.281 (n=6). Trace element data reveal extreme LREE enrichment, with La/v/Lu/v ~ 100. The trace element signature of Yanyare02 bears
Keywords: Pilbara Craton, lamproite, geochemistry, radiogenic isotopes, Ar-Ar geochronology, Proterozoic Email: e.matchan@pgrad.unimelb.edu.au
36
Geological Society of Australia Abstracts 90
Victorian Universities Earth and Environmental Sciences Conference The University of Melbourne, September 2008
AUTHOR INDEX A Allen, J. Arne, D. C Cas, R. Chandler, E. Chesler, R. Choo, B. Clement, A.M. Cristanelli, L. Currell, M.
26
9
31 28 35 20 21
16
Keogh, T.A. Kepert, J. Koch, R.D.
6 27 33
Lindsay, M. D. Lottermoser, B.G.
8 13
M Maas, R. Matchan, E.
35 36
2
N D de Sllva, S. Di Florio, V. Dowling, K.
Nelson, A.J.
31 11 10
P
30
Fairmaid, A. Folkes, C. Fu, B.
12 31 12
G Glover, F. H Harrison, B. Hergt, J. Hoiles, P.W. Holland, T. Honicke, S. J
12, 35, 36
Phillips, D.
E Ely, K.S.
17 35, 36 13 22, 23 4
17, 30 27 36 5
Viramonte, J.
31
27 9 13 34 31 17
10
Jakica, S.
32
W Wardle, R. Webb, J.A. Whitehead, P.W. Willcock, M.A.W. Wright, H. Wright, S.
K Kendrick, M.
12
Z Zohora, F.
37
10 27
R Rahman, A. Reeder, M. Sandiford, M. Scarbossa, D. Shee, S. Sharpies, J.P.