Neoarchean carbonates as archives of paleo-redox conditions on early Earth: Insights from metal isotope analyses of the Tumbiana Formation, Pilbara, WA

Farkas, Juraj1; Klaebe, Robert1, Scarabotti, Liam1, Stormberg, Jessica2, Spinks, Sam2

1Metal Isotope Group (MIG), Department of Earth Sciences, University of Adelaide, SA, Australia, 2CSIRO, Division of Mineral Resources, Perth, WA, Australia

The redox conditions of the earth’s surface environments are intimately linked to past changes in the atmospheric O2 levels, and thus to the long-term evolution of photosynthetic life on our planet. It is generally believed and accepted that Archean Eon is characterised by extremely low levels of atmospheric O2 concentrations with predominantly anoxic / euxinic marine and terrestrial environments; where the first significant rise in atmospheric O2 levels is documented much later during the Paleo-Proterozoic period at around 2.4 to 2.1 billion years (Byr) ago, the latter also called the Great Oxidation Event (GOE). This study aims to further constrain paleo-redox conditions during Neoarchean times by analysing selected metal isotope tracers and elemental concentrations in carbonate-rich samples from the Tumbiana Formation of the Fortescue Group in the Northern Pilbara Craton in WA, dated at ~2.7 Byr, which thus represent unique archives of paleo-environmental and redox conditions on early Earth. Here we analysed stable chromium isotopes (d53/52Cr variations), coupled with REEs and elemental Zn/Fe ratios, to infer past changes in redox conditions during the deposition of the Tumbiana Formation; and radiogenic strontium isotopes (87Sr/86Sr ratios) were used to test marine versus continental / lacustrine origin of the studied Neoarchean carbonates from the Fortescue Group. Interestingly, acquired results strongly support non-marine and thus likely lacustrine origin of the Tumbiana Formation carbonates; and more importantly our pilot data from redox-sensitive proxies (d53/52Cr and Zn/Fe ratios) point to an active redox cycling of Cr isotopes during the deposition of the Tumbiana Formation at ~2.7 Byr, thus challenging the prevalent views of strictly anoxic conditions during the Neoarchean. In addition, the above geochemical/isotope evidence for an active redox cycling (i.e., oxidation-reduction) of chromium and iron is documented in horizons with abundant stromatolitic carbonates, perhaps suggesting that local production of O2 via photosynthesizing microbial communities in restricted lacustrine settings could be partly responsible for the observed paleo-redox signals recorded in d53/52Cr and Zn/Fe tracers in carbonates from the Tumbiana Formation. We will discuss broader implications of the above findings for paleo-redox studies in deep times, including possibilities that predominantly anoxic and O2 depleted Archean earth’s surface environments could also harbor localised ‘oxygenated oasis’ in very specific depositional settings.


Biography

My research interest is focused on the application of metal isotopes and novel analytical techniques to low-temperature geochemistry, including earth system evolution studies, and isotope tracing of metals in near-surface environments. I completed my PhD at Uni Ottawa, Postdoctoral training at Harvard, and recently established Metal Isotope Group at UniAdelaide. 

Raiders of the lost continental arc: Deciphering the tectonic regime of eastern Australia during the Jurassic from analysis of tuff beds in the Surat Basin

Wainman, Dr Carmine1, McCabe, Prof Peter1, Reynolds, Dr Peter1

1Australian School of Petroleum and Energy Resources, University of Adelaide, Adelaide, Australia

Volcanogenic rocks are important components of the Late Triassic to Early Cretaceous infill of the Great Australian Superbasin, including the widespread deposition of air-fall volcanic ash (tuff) preserved in the Jurassic Walloon Coal Measures (WCM) of the Surat Basin. With the paucity of known igneous bodies in eastern Australia, these tuff beds provide important clues on the tectono-magmatic environment of eastern Gondwana during the Mesozoic. To better understand the source and character of the volcanic province, age-constrained tuffs (168 to 148 Ma) were analysed in detail. Bed thickness, petrography (supported by XRD data), zircon crystal size and their geochemistry were documented. New datasets reveal these buff-coloured tuffs, mostly preserved within coal seams, are between 0.01 and 2 m thick with sharp lower and upper contacts. They are dominated by splintery, angular quartz clasts (approx. 10–100 μm in diameter) supported in an amorphous, white-buff coloured matrix consisting of clay minerals (predominantly smectite). The same beds are poorly sorted, lightly compacted and lack any structure. Tuff isopach maps from the WCM show elongate lobes that thin from current day northeast to southwest (5 m to <1 m). Dated zircon crystals average 170 μm in size, are euhedral to tabular in shape, and have moderate U values (100 to 1000 pm) and elevated Y values (>500 pm). Integrating these datasets demonstrate that these tuffs were (1) produced from volcanoes fed by intermediate to felsic magmas, (2) that the prevailing paleowind direction was from east-southeast to west-northwest and (3) sourced from volcanoes approximately 280 to 1000 km away which erupted with a volcanic explosivity index (VEI) of approximately 8. We infer that these tuffs originated from a long-lived (late Palaeozoic to Cretaceous) continental arc related to the westward subduction of the paleo-Pacific oceanic crust beneath eastern Australia. These tuffs were most likely derived from the Whitsunday Igneous Association as supported from similar studies from Early Cretaceous strata of the Eromanga Basin. These previous findings will help better constrain the timing of when eastern Gondwana transitioned from a convergent to a divergent margin, and define future targets for ocean drilling to locate the parent igneous bodies in the Tasman Sea.


Biography

I am a Visiting Research Fellow at the University of Adelaide. I completed my PhD at the same university and received an MSci in Geology from the University of Southampton. My research focuses on Permian and Jurassic coal-bearing strata in Australia, and the Mesozoic evolution of Australia’s southern margin.

Recognition of an Early Cretaceous Continental Arc in Eastern Australia

Spandler, Carl1, Henderson Bob2, Foley, Elliot2, Roberts, Eric2, Kemp, Tony3

1The University of Adelaide, Adelaide SA 5005, 2James Cook University, Townsville, QLD 4811, 3The University of Western Australia, Perth, WA 6907

The Phanerozoic tectonic setting of eastern Australia involved two separate regimes. The older setting was a Cambrian to Triassic active convergent margin as registered by a succession of orogenic systems collectively grouped as the Tasmanides. The younger setting was a passive margin, driven by plate divergence that initiated in the Cretaceous, and continues to characterize eastern Australia. The tectonic setting of eastern Australia during the gap between these contrasting tectonic regimes (approx. 130 m.y. from the late Triassic to Cretaceous) has been poorly documented and remains open to question. While extensive continental detritus of this age is preserved in the Great Artesian Basin, recognized igneous activity is restricted to the Whitsunday Igneous Province that formed from 132 Ma to 95 Ma.

Here we investigate a suite of igneous rocks/units that includes the Grahams Creek Formation (>0.25 M km3) and a series of small plutons and volcanic units that are exposed in the region between the Sunshine Coast and Maryborough in SE Queensland. The plutonic rocks range from I–type, hornblende-rich gabbros and diorites, to granodiorites, and quartz syenites, while the Grahams Creek Formation consists of a thick sequence (up to 1200 metres) of volcanic to volcaniclastic rocks of basaltic to dacitic composition. Both plutonic and volcanic components have distinctive subduction-related trace element compositions, including relative depletion in Ti, Nb and Ta, and enrichment in Pb, Sr, K, Rb, Th, U, Ba and Cs. These compositions are typical of hydrous magmatic rocks from continental arc settings. Uranium-Pb dating of magmatic zircons from these samples returned ages between 145 and 140 Ma; an age range that is distinctly older that the Whitsunday Igneous Province. The initial Hf and O isotope composition of these zircons (εHf = +8 to +12.5; δ18O = +5.7 to +6.5) is consistent with a juvenile mantle source for these magmas.

The recognition of this new suite of magmatic rocks, together with new chemical analyses of mafic rocks from the Whitsunday Igneous Province and detrital zircon records of quartzo-feldspathic sedimentary sequences of the Great Artesian Basin (see Foley et al. 2020, this session), allow a re-evaluation of the tectonic setting of eastern Australia across the Mesozoic. We propose that the plate convergence regime along eastern Australia that formed the New England Orogen persisted across the Triassic, Jurassic and into the Cretaceous, with the newly-recognised arc rocks representing the youngest episode of continental arc magmatism recorded on the Australian continent.  Eastwards rollback of the slab in the Early Cretaceous led to continental extension and opening of a continental back-arc (analogous to the present-day Okinawa Trough) that formed the Whitsunday Igneous Province. Continued slab rollback and extension of the overlying plate in the late Cretaceous and Cenozoic lead to rifting and fragmentation of the eastern continental margin to form the current configuration of the eastern Australia-Zealandia, where large tracts on thinned continental crust remain submerged.


Biography

Carl Spandler is a petrologist/geochemist with interest in broad aspects of geology, particularly crustal growth processes, plate tectonics, mantle evolution and critical minerals ore systems.

Jurassic physiography of southeastern Australia: Evidence from detrital zircon from the Nambour Basin

Henderson, Robert 1, Foley, Elliot1, Roberts, Eric1

1James Cook University, Townsville, QLD 4811

Jurassic fluviatile infill of the Nambour Basin consists largely of quartzose sandstone of the Myrtle Creek and Landsborough formations and succeeding heterolithic sandstone, shale and coals of the Tiaro Coal Measures. Detrital zircon age spectra for representative sandstone samples constrain the ages and sediment sources of these units. Maximum depositional ages from zircon, broadly consistent with published biostratigraphic age determinations, assign this succession as Early to Middle Jurassic (195-163 Ma). With a coastal location in southern Queensland, these units represent the easternmost record of Jurassic sedimentation for Australia.

Zircon age spectra from Early Jurassic samples of the Myrtle Creek Formation are dominated by a 650 – 500 Ma (Pacific-Gondwana) age cluster, with a Grenville age cluster (1300-950) also showing prominence. Detrital zircon of these ages is characteristic of Cambro-Ordovician metasediments of the Tasmanides as widely represented in southeastern Australia. Rocks of this Tasmanide assemblage stood as epeirogenic Jurassic upland, shedding sediment northwards and eastwards across southeast Queensland. Transport vectors obtained for the Myrtle Creek Formation fluviatile sandstone horizons support this conclusion.   Devonian – Triassic ages of detrital and igneous zircon characteristic of the New England Orogen, which abuts the Nambour Basin and forms a broad crustal tract to its west, are sparingly represented in these samples.

Relief across the orogen in southeastern Australia, as generated by the Permo-Triassic (260-230 Ma) Hunter Bowen Orogeny, had therefore been reduced towards base level, with little contribution to ongoing erosion and sediment production, by the Early Jurassic (~190 Ma). By implication, the base level surface forming the floor to the Great Artesian Basin, marking a unconformity of remarkable extent, continued eastwards as a surface of low relief across much of the New England Orogen.  Detrital zircon from sandstone samples of the Middle Jurassic Tiaro Coal Measures indicate a continuing provenance contribution from Cambro-Ordovician Tasmanide metasediments but also from a more pronounced New England Orogen source, suggesting some physiographic rejuvenation of this crustal sector subsequent to the Early Jurassic.

Jurassic aged zircon is scarce in most samples. However, it is well represented in a sample from the Myrtle Creek Formation and dominates the detrital zircon age spectrum of an arkosic sample from the Tiaro Coal Measures. As no source terrain for Jurassic zircon is known for the crustal fabric of eastern Australia, it must have been derived from igneous assemblages on continental crust to the east, now represented by submerged northern Zealandia, which rifted from the Australian continent during Late Cretaceous – Paleocene. An eastern source is supported by westerly paleocurrent directions measured for the sandstone intervals from which these samples were obtained.


Biography

Researcher with long term interests in the Tasmanide orogenic system, especially the Mossman and New England Orogens. Research interests also in Paleozoic and Mesozoic sedimentary basins located in Queensland inclusive of stratigraphy, sedimentology, paleontology and tectonic setting with contemporary utilisation of detrital zircon LAICPMS geochronolgy in basin studies

Jurassic Arc? Reconstructing the Lost World of eastern Gondwana

Foley, Elliot1, Henderson, Robert1, Roberts, Eric1, Kemp, Tony2, Spandler, Carl3

1James Cook University, Townsville, QLD 4811, 2The University of Western Australia, Perth, WA 6009, 3The University of Adelaide, Adelaide SA 5005

The tectonic setting of the east Gondwana margin during the Jurassic and Early Cretaceous is an enduring geological unknown. Whereas Paleozoic to early Mesozoic (~520 to 220 Ma) accretionary orogenic domains in eastern Australia are considered an exemplary record of convergent margin processes, the Late Triassic to Cretaceous represents an enigmatic gap in this record due to the paucity of exposed igneous and metamorphic rocks. This latter witnessed the deposition of vast quantities (>1.5 x 106 km3) of sediment into the Great Australian Superbasin, including Jurassic silicic tuff horizons and a substantial Cretaceous component identified as volcanogenic.

The nature of magmatism that provided this volcanogenic material is debated, with two principal hypotheses posited. One suggests a continental magmatic arc enduring from the Carboniferous to mid-Cretaceous. The second model favours intraplate, rift-related magmatism unrelated to subduction, exemplified by the early-mid Cretaceous Whitsunday Igneous Province, a silicic large igneous province (SLIP) generated in the prelude to rupture of east Gondwana in the Late Cretaceous. Resolution of this question has been hampered by the sparse Jurassic-Cretaceous igneous record for eastern Australia. To overcome this deficiency, we investigated detrital zircon from the Great Australian Superbasin as a proxy record for subjacent igneous activity, employing U-Pb geochronology and Hf isotopic analysis to evaluate Mesozoic magmatism and clarify this enigmatic episode of east Gondwana crustal evolution.

Detrital zircon ages indicate that magmatism along the east Gondwana margin continued into the mid Cretaceous, with short-lived (~10 Myr) pulses of Mesozoic magmatic activity indicated by peaks at ~160, ~140, and ~100 Ma. A trend of increasing igneous activity, from the Jurassic towards eventual Late Cretaceous continental rupture of east Gondwana, as predicted by the SLIP hypothesis, is not supported by the detrital zircon record. Hf isotopic analysis of dated zircons shows a strongly positive εHf signature (+8 to +12) throughout the Mesozoic to ~95 Ma indicative of juvenile sources for the original igneous parent rocks. Similar positive εHf signatures are characteristic of Permian – Triassic granitic rocks of the New England Orogen for which a continental magmatic arc setting has been long accepted.

A potential Australian igneous source for Cretaceous zircon, the Whitsunday Igneous Province, is of limited aerial extent and a Jurassic source is unknown. Northern Zealandia, now submerged, formed the eastern borderland of east Gondwana prior to the Late Cretaceous, and must have been the main locus of Jurassic and Cretaceous magmatism.


Biography

Elliot Foley is a PhD Candidate at James Cook University and a member of the multidisciplinary Jurassic Arc Research Group.  His research focuses on the sedimentology, stratigraphy, provenance and hydrocarbon potential of basin fill in the northern sector of the Jurassic-Cretaceous Great Australian Superbasin.

Tectonic evolution and crustal growth processes revealed by detrital zircon petrochronology: Insights from dispersed Paleozoic-Mesozoic sedimentary basins of Zealandia

Campbell, Matthew J 1, Rosenbaum, Gideon 1, Allen, Charlotte M. 2, Spandler, Carl 3

1School of Earth and Environmental Sciences, The University of Queensland, Brisbane, QLD, Australia,  2Institute for Future Environments, Queensland University of Technology, Brisbane, QLD, Australia, 3Geosciences, James Cook University, Townsville, QLD, Australia.

Paleozoic-Mesozoic supra-subduction units, which originally formed along the paleo-Pacific margin of east Gondwana, are now preserved in eastern Australia, Antarctica and Zealandia. Previous works have characterized the temporal and geochemical history of magmatism within this broad accretionary orogenic system but the Zealandia continent remains a problematic piece of the Gondwana puzzle due to (1) 94% of the continent being submerged beneath the southwest Pacific Ocean and (2) a number of major phases of deformation that culminated in the oceanward dispersal of continental fragments of Zealandia. Here we reconstruct the Paleozoic and Mesozoic evolution of the active continental margin of Zealandia (eastern Gondwana), using a combination of detrital zircon geochronology, trace-element geochemistry, and Hf isotope data from several Paleozoic-Mesozoic terranes in New Zealand and New Caledonia. We find that zircon grains dated 360–160 Ma from New Zealand are characterized by εHfi (+15 to +2) and trace-element compositions typical of predominantly juvenile magmatic sources. In contrast, the εHfi (+15 to –5) and trace-element compositions of detrital zircon grains dated 245-140 Ma from New Caledonia reflect a mix of juvenile and evolved crustal sources. Secular trends in trace-element and Hf isotope compositions of zircon grains suggest that magmatism and continental crustal growth in Zealandia during the Devonian–Cretaceous were controlled by switches from trench advance to trench retreat. Orogenesis and crustal growth were controlled by a long-lived westward-dipping subduction system, which during the Permian–Triassic, was intermittently affected by distinct phases of arc accretion (e.g., of the Brook Street intra-oceanic arc) and orogenesis (e.g., driven by trench advance). These phases of orogenesis coincided with the Gondwanide Orogen (265–230 Ma), which might have been controlled by a plate-scale reorganization event following the final assembly of Pangea supercontinent.


Biography

Recent PhD graduate in geology from the University of Queensland. My PhD was focused on the Paleozoic to Mesozoic tectonic history and crustal architecture of the southwest Pacific region (Zealandia).

Cretaceous Evolution of Zealandia dictated by congested subduction

Betts, Peter1, Moresi, Louis2, Whittaker, Joanne3, Miller, Meghan2

1School of Earth Atmosphere and Environment, Monash University, Melbourne, Australia, 2Research School of Earth Sciences, Australian National University, Canberra, Australia, 3Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia

Congested subduction occurs when buoyant lithosphere within the downgoing plate interacts with the with the convergent margin trench and prevents the slab from subducting in the region of collision. This can trigger several dynamic behaviours in the slab including slab tearing beneath the congestion and roll back of the trench away from the collision zone.  Congested subduction also drives contemporaneous shortening and extension along different parts of the overriding plate, and has the potential to dismember and segment subducting slabs.

During the Cretaceous collision of the Hikurangi Plateau with the east Gondwana margin triggered a major re-organisation of the margin culminating in the opening of the Tasman Sea and separation of Zealandia from Gondwana.  Tectonic models for this plateau accretion have proposed collision between the plateau and Campbell Plateau (South Island of New Zealand) at ca. 100 Ma, which triggered the opening of the Tasman Sea at ca 84 Ma.   These models are appealing because they explain the present-day relationship between the Hikurangi Plateau and the New Zealand along the Pacific-Australia plate margin. 

In this abstract, we provide an alternative model for the collision of the Hikurangi Plateau and Gondwana that is informed by numerical modelling of congested subduction.  We present this alternative tectonic model as a series of G-plates reconstructions.  Our new model requires collision of the Hikurangi Plateau with the Gondwana along the North Island of New Zealand, rather than the South Island.  Suturing of the Hikurangi Plateau with the North Island resulted in crustal shortening in front of the collision zone and triggered collapse of the Gondwana margin to the south and north.  Initiation of asymmetric trench roll back to the south is evidenced by the ubiquitous extension in the overriding plate, affecting the Campbell Plateau and Chatham rise.  Asymmetric opening of Tasman Sea and opening of the Bounty Trough at 84 Ma.  Counter clockwise rotation of the Chatham and Campbell plateaus segmented the slab along the Gondwana margin.  Soft collision of southern Zealandia (Chatham and Campbell Plateau) along the southern margin of the Hikurangi Plateau occurred at ca 70 Ma and stable subduction was established outboard of this accreted margin.  In this model, the Alpine fault initiated as a sinistral fault at the transition between trench advance in the North Island and trench roll-back to the south. 


Biography

Peter Betts has a diverse portfolio of research that addresses tectonic problems through Earth history.  He is currently working on the Tectonic process related to congested subduction, the opening of new oceans, and the role of inherited structures on continental reactivation.

Interpreting and validating trans-lithospheric faults in the Central Andes to investigate their control on the localisation of giant porphyry copper deposits

Farrar, Alexander1,2, Cracknell, Dr Matthew1, Cooke, Professor David1, Hronsky, Dr Jon3,4, Piquer, Dr Jose5

1Universiity Of Tasmania, Hobart, Australia, 2First Quantum Minerals, Santiago, Chile, 3Western Mining Services, Perth, Australia, 4University of Western Australia, Perth, Australia, 5Universidad Austral de Chile, Valdivia, Chile

The central Andes (between latitudes of 14°S and 35°S) accounts for approximately 40% of the world’s annual copper production and is the most important copper province on the planet. However, since 1998, just one giant porphyry copper greenfield discovery has been made in the central Andes. Post-mineralisation cover consisting of transported gravels and young volcanics make up at least 50% of the surficial outcrop of the central Andes and of the 60 or so known giant Cu ± Au ± Mo deposits, only three giant ore deposits have been discovered beneath these surficial materials in the greenfields domain. Therefore it is likely that many concealed, undiscovered giant porphyry copper deposits are waiting to be discovered. However, no proven effective exploration process exists that enables explorers to consistently achieve economic greenfield discoveries through cover.

Giant porphyry copper deposits tend to cluster in discrete geographic “camps” of a similar age. This indicates that exceptional transient geologic processes have affected localised regions of the crust prior to and during the age of mineralisation and that the formation of giant porphyry deposits is non-random. Key predictive geological features of giant porphyry Cu deposits are the structural pathways (basement faults) that focus fluid and magma flow from the mantle to upper crust. Nevertheless, these so called trans-lithospheric faults (TLFs) are notoriously difficult to identify in the field due to their subtle surficial characteristics, complex multi-stage reactivation history and continental-scale. As a result, the notion of TLFs has, until recently, been treated with scepticism by many in the geologic community.

This research focuses on identifying and mapping the continental-scale trans-lithospheric structural architecture of the central Andes through the integration and interpretation of multiple geoscience datasets supported by field observations. Datasets used in this analysis include geophysical inputs such as airborne magnetics, regional gravity, magneto-tellurics and seismic epicentres as well as geologic reconstructions through time from the Proterozoic to present, which map out inherited basement architecture as well as regions of rapid crustal thickening or thinning. Fieldwork undertaken in the regions of the interpreted TLFs demonstrates that on the surface they are expressed as linear zones of brittle faulting, tens of kilometres wide and hundreds of kilometres long, consisting of thousands of individual fault planes. This is interpreted to reflect the upper crustal propagation of the underlying zone of basement weakness through younger sequences in the geologically active convergent plate margin.

A map of the TLFs across the central Andes shows that the TLFs have a fractal distribution with N, NW and NE strikes. A prominent relationship exists with the location of known giant porphyry deposit camps occurring where two or more TLFs meet. Such regions are inferred to have been loci of deep-seated strain-anomalies which have localised dilation and increased permeability, during transient changes to the regional stress field. Regions adjacent to the intersection of two or more TLFs that overlap with the magmatic arc during metallogenic epochs (themselves transient geodynamic anomalies) are deemed to represent valid exploration targets in this model.


Biography

Began in the mining industry in 2007 with Xstrata in Mt Isa. In 2009 joined First Quantum Minerals based in DRC and Zambia. From 2013-2020 based in South America with First Quantum running greenfields project generation. Currently undertaking a PhD at University of Tasmania concerning fundamental emplacement controls on porphyries.

Unravelling the “late” evolution of the Gawler Craton: high T/P metamorphism, tectonism and magmatism of the Yorke Peninsula, South Australia

Bockmann, Mitchell1,2, Hand, Professor Martin1,2, Morrissey, Dr Laura3,1, Payne,Dr Justin4,3,1, Teale, Graham5, Conor, Associate Professor Colin4, Dutch, Dr Rian6,2

1Departments of Earth Science, University Of Adelaide, Adelaide, Australia, 2Mineral Exploration Cooperative Research Centre, University of Adelaide, Adelaide, Australia, 3Mineral Exploration Cooperative Research Centre, Future Industries Institute, University of South Australia, Adelaide, Australia, 4UniSA STEM, University of South Australia, Adelaide, Australia, 5Teale and Associates Pty Ltd, Prospect, Australia, 6Department for Energy and Mining, Geological Survey of South Australia, Adelaide, Australia

The early Mesoproterozoic is a geologically active time in the Gawler Craton, recording widespread magmatism, deformation, metamorphism and mineralisation. Much of this activity occurs within the time period of 1600–1575 Ma, during the Hiltaba tectonothermal event and associated the worldclass Iron-oxide–Copper–Gold (IOCG) mineralisation, which has focussed attention on this timeline. This event has often been considered the timing of ‘cratonisation’ as there was perceived to be little tectonic activity that post-dates this timeline. However, sporadic evidence across the Gawler Craton for metamorphism, deformation and minor magmatism post-dating this major event has indicated tectonic activity extends beyond this age. This study further highlights the importance and extent of post-1575 Ma activity in defining the modern-day structural and metamorphic architecture of the Gawler Craton.

The Yorke Peninsula in the southern Gawler Craton is a highly prospective region for IOCG mineralisation, as it hosts the historically significant Moonta and Wallaroo mines and more recently discovered Hillside deposit. Despite extensive evidence for early Mesoproterozoic hydrothermal fluid activity and great potential for mineralisation, the Yorke Peninsula is incredibly understudied with modern analytical techniques.

Here we present evidence for high T/P metamorphism from the Yorke Peninsula at c. 1555 Ma, with peak metamorphic constraints of c. 3.5 kbar, 660°C and c. 4.2 kbar, 700°C from two samples taken approximately 35km apart. In addition, monazite U–Pb geochronology also provides evidence for  shear zone activation at this time, along with possible evidence for re-activation of the Pine Point Fault as young as 1500 Ma; significantly post-dating mineralisation at the Hillside deposit. Apatite U–Pb cooling ages from these rocks provide relatively young ages between 1460–1400 Ma, indicating that these rocks remained at elevated temperatures for an extended period following the metamorphic peak, supporting a long-lived thermal driver for metamorphism. The record of this post-Hiltaba event is also manifest in published monazite and zircon ages from the Barossa Complex on the Fleurieu Peninsula, signifying that this event impacted the entire south-eastern Gawler Craton. The metamorphic conditions and prolonged time at depth indicated by relatively young apatite U–Pb cooling ages from the Yorke Peninsula are consistent with thinned continental crust, implying that the south-eastern Gawler Craton was in an extensional setting after the Hiltaba Event. Post-Hiltaba activity is distinct from metamorphism and deformation associated with the Hiltaba Event, which is also recorded within the south-eastern Gawler Craton, but typically with lower thermal gradients. The metamorphism reported in this study has long been assumed to be linked to the Hiltaba Event, along with much of the Mesoproterozoic magmatism, deformation and mineralisation on the Yorke Peninsula. This study reveals that the c. 1515 Ma Spilsby Suite is not the only expression of post-Hiltaba activity on the Yorke Peninsula and demonstrates that the thermal and tectonic footprint of post-Hiltaba events is much greater than previously interpreted, suggesting that some of the mineralisation hosted within the region (e.g. Moonta-Wallaroo) may also be postHiltaba, with evidence for potential thermal drivers, fluid sources and deformation in operation after this time.

Biography

A third year MinEx CRC PhD student from the University of Adelaide, studying the tectonic setting of early-Mesoproterozoic mineral systems in the Gawler Craton, South Australia

Mineral Systems of the Capricorn Orogen through time

Occhipinti, Dr Sandra , Metelka, Dr Vaclav1, Lindsay, Dr Mark2, Aitken,Dr Alan2

1CSIRO, Kensington, Australia; 2Centre of Exploration Targeting, University of Western Australia, Crawley, Australia

Opening up greenfields regions for minerals exploration programs is best facilitated through the understanding of regional minerals prospectivity. The Capricorn Orogen is a greenfields-dominated region, for which a multicommodity mineral systems analysis has been completed forming the basis for new prospectivity analysis and mapping. Known mineral occurrences or deposits in the region formed between the Paleoproterozoic and Neoproterozoic. Mineralisation can be related to basin development and orogenesis in the region, in turn related to periods of supercontinent assembly and breakup. These were manifested in the region through the contractional 2005–1950 Ma Glenburgh, 1830–1780 Ma Capricorn, and c. 1030–950 Ma Edmundian and 920–850 Ma Kuparr orogenies. These periods of orogenesis were preceded and interspersed with periods of subsidence, perhaps including the 1680–1620 Mangaroon Orogeny, which led to the development of volcanosedimentary and sedimentary basins throughout the region. Prospectivity models were generated for several commodity groups of various ages and ore genesis mechanisms, including combinations of Ni, Cu, PGEs, V, Ti, Au, Pb, Zn, channel Fe and U. The work has found a link between key mineral systems and a spatial relationship between disparate styles of mineral deposits in the region. Crustal-scale tectonic architecture was analysed by allying a 2D map view geological-geophysical interpretation with 2.5D magnetic and gravity joint inversions of selected profiles, a 3D Moho model, and by inference from 2D and 3D magnetotelluric models, 2D reflection seismic images and 3D passive seismic models from the region.  This work clearly illustrates that different ‘zones’ of the Capricorn Orogen are prospective for different commodity groups due to the tectonic environment in which they developed. Major crustal-scale deformational zones intrinsically control the location of known ore deposits in the area, and are inferred to be sites of fluid migration associated with ore deposition. Of these, some are considered to be of Archean origin, whereas others are thought to have first developed during the early Paleoproterozoic. In both cases, many structures have been re-activated through time, influencing the formation of basins over them and perhaps the formation of ore deposits.


Biography

Sandra Occhipinti is a geologist with over 20 years experience in regional mapping, geophysical interpretation, mineral systems analysis and structural geology. She is the research director of the Discovery Program, CSIRO Mineral Resources

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About the GSA

The Geological Society of Australia was established as a non-profit organisation in 1952 to promote, advance and support Earth sciences in Australia.

As a broadly based professional society that aims to represent all Earth Science disciplines, the GSA attracts a wide diversity of members working in a similarly broad range of industries.