Following deep seismic reflection surveys on the Yilgarn and Pilbara cratons by Geoscience Australia with the Geological Survey of Western Australia and on the Superior Craton by the Canadian Lithoprobe program, these cratons are now some of the best surveyed Archean regions on Earth. We present seismic images that highlight how variations in crustal architecture relate to differences in Archean tectonic processes between cratons. All cratons are characterized by a mostly non-reflective 4–12 km-thick uppermost crust due to the presence of large granitoid plutons and gneissic domains. Localized regions of upper crustal seismic reflectivity are typically interpreted as supracrustal rocks and mafic sills or faults and shear zones. The middle and lower Archean crust contains variably complex geometries of relatively high amplitude reflections, though in some regions, such as the Eastern Goldfields Superterrane and the Abitibi Greenstone Belt, the lower crust appears less reflective than the middle crust. Crustal thicknesses vary from 30 km in the eastern Pilbara to 35–40 km across much of the Yilgarn and Superior, though thicknesses as great as 45–52 km occur locally in the latter two cratons. The characteristics of the Archean crust-mantle boundary, or Moho, which is commonly well-defined, differs between cratons, indicating significant variations in the tectonic processes that have driven the final stages of crustal evolution. Dipping reflections in the uppermost mantle linked to convergent crustal structures are interpreted as relict subduction scars. In the southern Superior Craton, Moho offsets and northdipping reflections in the middle and lower crust arose through successive underthrusting of Meso-Neoarchean island arcs, oceanic plateaux and microcontinental fragments, as they accreted against a pre-existing northern nucleus (e.g. North Caribou and Opatica terranes). Seismic reflection lines reveal a doubly vergent orogen above north-dipping mantle reflections that indicate subduction drive accretion. Post-orogenic crustal extension, which is inferred from crustal-scale normal shear zones and dropped greenstone belts, has not erased the original accretionary crustal architecture. In contrast, in the Yilgarn Craton interior, accretionary structures are less clear and there are no prominent offsets in the Moho. In the Youanmi Terrane, which represents the cratonic nucleus, a pervasive fabric of listric east-dipping mid-crustal reflections soles out into the upper part of subhorizontal lower crustal reflections. We interpret this reflective fabric to be the result of widespread crustal collapse during the late stage of craton evolution at c. 2.65–2.6 Ga that also produced subsidence of the upper crust. Though terrane boundaries can be identified in seismic data across the Eastern Goldfields Superterrane, these boundaries have commonly been modified by extension, which also overprinted any accretionary lower crustal structures, perhaps simultaneous with widespread intrusion of post-tectonic melts. Exhumation of moderately reflective, amphibolite to granulite facies crust in the Narryer Terrane above dipping mantle reflectors indicates that shortening along the northwestern edge of the Yilgarn Craton was subduction driven. In the eastern Pilbara Craton, shallowly dipping to subhorizontal reflections in the middle and lower crust preclude crustal-scale vertical tectonic movements and imply that the vertical displacements inferred from surface mapping were largely confined to the upper crust. <div>The abstract accompanies a talk the describes the architecture and and related tectonic processes of several Archean cratons based on reflection seismic interpretations. </div> This Abstract was submitted to & presented at the 2023 6th International Archean Symposium (6IAS) 25 - 27 July (https://6ias.org/)

<div><strong>Output Type:</strong> Exploring for the Future Extended Abstract</div><div><br></div><div><strong>Short Abstract: </strong>Knowledge of lithospheric structure is crucial information for resources exploration and deepening understanding of natural hazards. Available tomographic models of the Australian lithosphere often agree on large scale features, but in detail significant differences remain. Consequently, there is a growing need for a fully verifiable lithospheric model of Australia. Geoscience Australia has committed to develop such a model and share all results and datasets involved in model building. Here we present the first results of a full waveform inversion tomography model of Australia lithosphere down to a period of 70 s potentially able to resolve half wavelengths across continental Australia. Our model is based on seismic records from the National Seismic Network and legacy datasets with the addition of data from the currently deployed continental-scale 2° AusArray survey, which includes stations installed in previously inaccessible areas. We start with 193 earthquakes (moment magnitude (Mw) 6.2–7.5) and add 165 more earthquakes (Mw &gt;5.0) once the model progressed to a period of 70 s. Model resolution will improve over time as more data become available and more time is allowed for computation and quality control. As further iterations continue, and the inversion frequency range expands to higher frequencies, body waves can be exploited in full to constrain the model in detail and provide enough information for all components of the wavefield, building high-resolution tomographic models at a period of 40 s and below. Our model reveals previously observed first order features while revealing finer detail across much of continental Australia.</div><div><br></div><div><strong>Citation: </strong>Holzschuh, J., Gorbatov, A., Hejrani, B., Boehm, C. &amp; Hassan, R., 2024. Tomographic model of the Australian region from seismic full waveform inversion. In: Czarnota, K. (ed.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, https://doi.org/10.26186/149404</div>

In recent years there has been a considerable expansion of deployments of portable seismic stations across Australia, which have been analysed by receiver function or autocorrelation methods to extract estimates of Moho depth. An ongoing program of full-crustal reflection profiles has now provided more than 25,000 km of reflection transects that have been interpreted for Moho structure. The Moho dataset is further augmented by extensive marine reflection results. These new data sources have been combined with earlier refraction and receiver function results to provide full continental coverage, though some desert areas remain with limited sampling. The dense sampling of the Moho indicates the presence of rapid changes in Moho depth and so the Moho surface has been constructed using an approach that allows different weighting and spatial influence depending on the nature of the estimate. The inclusion of Moho results from gravity inversion with low weighting helps to resolve the continent-ocean transition and to provide additional control in the least sampled zones. The refined distribution indicates the presence of widespread smaller-scale variations in Moho structure. Strong lateral contrasts in crustal thickness remain, but some have become more subdued with improved sampling of critical areas. The main differences from earlier results lie in previously poorly sampled regions around the Lake Eyre Basin, where additional passive seismic results indicate somewhat thicker crust though still witha strong contrast in crustal thickness to the cratonic zone to the west. Appeared in Geophysical Journal International, January 2023

<div>Ideally when combining different 3D seismic surveys differences in acquisition parameters warrant full pre-stack reprocessing from field data. However, there are occasions where this is not possible due to time, financial or data access constraints; a valuable alternative is post-stack merging and enhancement of existing migrations. The offshore Otway Basin was the subject of such a project, the objective of which was to produce a regularised and seamless 3D dataset of the highest possible quality, within a two-month turnaround time. The input migrated volumes varied by data extent, migration methodology, angle range and grid orientation. 14 input volumes totalling 8,092 km2 were post-stack merged and processed to produce a continuous and consistent volume, enabling more efficient and effective interpretation of the region. The surveys were regularised onto a common grid, optimised for structural trend, prior to survey matching. DUG’s mis-tie analysis algorithm, applied over a time window optimised for interpretation of key</div><div>events, was used to derive corrections for timing, phase and amplitude, using the Investigator North survey as a reference. This was followed by time-variant spectral and amplitude matching, with gain corrections applied, to improve continuity between volumes. Additional enhancements including noise removal and lateral amplitude scaling were also applied. The final merged volume offers significant uplift over the inputs providing better imaging of structure and event and dramatically improving the efficiency and quality of interpretation. This enables rapid reconnaissance of the area by explorers. Presented at the Australian Energy Producers (AEP) Conference & Exhibition

Interpretation of 2014–2015 deep crustal seismic reflection and magnetotelluric data has revised the architecture and geodynamic framework of western Queensland, with implications for the assembly and dispersal of the supercontinents Nuna, Rodinia and Gondwana. In the Mount Isa Province, crustal-scale boundaries of the Leichhardt River Domain, Kalkadoon-Leichhardt Domain and Eastern Subprovince are mapped in the third dimension. The Leichhardt River and Kalkadoon-Leichhardt domains have similar Nd isotopic T 2DM model ages to provinces to the west, indicating they were part of ancestral North Australian Craton (NAC); the Eastern Subprovince is a separate terrane, with the Pilgrim Fault a collisional suture. The Gidyea Suture Zone separates the Mount Isa Province from the subsurface Numil Seismic Province. To the east, the west-dipping Yappar Fault separates east-dipping structures in the west from west-dipping structures in the east, forming a classic doubly vergent orogen within the upper plate of a convergent margin. The northwestern boundary of the Bernfels Seismic Province, the Kynuna Fault, truncates the Gidyea Suture Zone, implying this seismic province was welded to the NAC prior to initial deposition of the Etheridge Province. The Cork Fault truncates the north-south grain of the Mount Isa Province; the easternmost part of the NAC has been excised, presumably during breakup of Nuna. The subsurface Brighton Downs Seismic Province, formerly part of the northern Thomson Orogen, is a discrete seismic province, located between the NAC and the Thomson Orogen, and welded to the NAC during the accretion of Rodinia. Basement to the Thomson Orogen is a collage of microplates, accreted to the Brighton Downs Seismic Province during the assembly of Gondwana. By 530 Ma, eastern Australia faced an open Pacific Ocean, with the Thomson Orogen in a backarc setting. Thus, northeastern Australia contains a record of repeated continental accretion and breakup over at least three supercontinent cycles. <b>Citation: </b>Russell J. Korsch, Michael P. Doublier, Dominic D. Brown, Janelle M. Simpson, Andrew J. Cross, Ross D. Costelloe, Wenping Jiang, Crustal architecture and tectonic development of western Queensland, Australia, based on deep seismic reflection profiling: Implications for Proterozoic continental assembly and dispersal, <i>Tectonophysics</i>, Volume 878, 2024, 230302, ISSN 0040-1951, https://doi.org/10.1016/j.tecto.2024.230302.

<div>The architecture of the lithosphere controls the distribution of thermal, compositional and rheological interfaces. It therefore plays a fundamental role in modulating key ore-forming processes including the generation, transport, fractionation, and contamination of melts.&nbsp;Recognition of its importance has led to renewed efforts in recent years to incorporate constraints on lithospheric structure into the targeting of prospective regions for mineral exploration. One example is a suggested relationship between the genesis of porphyry copper deposits – known to be associated with evolved, silica-rich magmas – and the thickness of the crust.&nbsp;Here, using a new compilation of spot measurements, we explore the utility of crustal thickness as an exploration tool for porphyry copper deposits.</div> This Abstract was submitted & presented at the 2022 American Geophysical Union (AGU) Fall Meeting 12-16 December (https://www.agu.org/Fall-Meeting-2022)

Geoscience Australia has undertaken a regional seismic mapping study of the offshore Otway Basin extending across the explored inner basin to the frontier deep-water region. Seismic interpretation covers over 18000 line-km of new and reprocessed data acquired in the 2020 Otway Basin seismic program and over 40000 line-km of legacy 2D seismic data. We present new basin-scale isochore maps that show the distribution of the Cretaceous depocentres. Maps for the Lower Cretaceous Crayfish and Eumeralla supersequences, together with those recently published for the Upper Cretaceous Shipwreck and Sherbrook Supersequences, completes the set of isochore maps for the main tectonostratigraphic basin intervals. Mapping of basement involved faults has revealed structural fabrics that have influenced depocentre development. The tectonostratigraphic development of depocentres and maps of deep crustal units delineate crustal thinning trends related to late Cretaceous extension phases. This work highlights the need to review and update structural elements. For example, the boundary between the Otway and Sorell basins is now geologically constrained. The refinements to the tectonostratigraphic evolution of the Otway Basin presented here have important implications for the distribution and potential maturity of petroleum systems, especially with regard to heat flow associated with crustal extension. Presented at the 2024 Australian Energy Producers Conference & Exhibition (AEP) (https://energyproducersconference.au/conference/)

<div><strong>Output type: </strong>Exploring for the Future Extended Abstract</div><div><br></div><div><strong>Short Abstract: </strong>Seismic tomography has been used for more than 50 years to map the seismic velocity structure of Earth’s interior. Here, we use data from the Exploring for the Future program, AusArray 2o deployment, to perform ambient noise tomography of the Australian continent. In this approach, stacks of cross-correlations of background seismic noise recorded by pairs of seismometers are employed to extract an approximation to the surface wave trains travelling between the seismometers. We have developed a semi-automatic approach to estimate dispersion properties of surface waves as a function of frequency at 0.01 – 1 Hz and deployed the largest ever network of broadband seismometers across the country to image the continental crust of Australia. In this study, we present an ambient noise tomography map of the Australian continent at 0.4 Hz (2.5 seconds), which is sensitive to the top 3 km of the Earth’s crust. Our model shows improved resolution across the country, for example, we observed a large low-velocity anomaly (~2.5 km/s) which delineates the shape of the entire Caning basin in Western Australia. This basin has never been imaged at this detail before, as previous tomographic studies do not measure surface wave velocity up to 0.4 Hz and do not have stations deployed in this area. The outcome demonstrates the utility of the ambient noise tomography method of imaging first-order features, that could be built upon for resource potential assessments.</div><div><br></div><div><strong>Citation: </strong>Hejrani B., Hassan R., Gorbatov A. & Zhao J., 2024. Towards continental-scale ambient noise tomography of Australia: a preliminary result from AusArray data. In: Czarnota, K. (ed.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, https://doi.org/10.26186/149637</div>

<div>Lithospheric structure and composition have direct relevance for our understanding of mineral prospectivity. Aspects of the lithosphere can be imaged using geophysical inversion or analysed from exhumed samples at the surface of the Earth, but it is a challenge to ensure consistency between competing models and datasets. The LitMod platform provides a probabilistic inversion framework that uses geology as the fabric to unify multiple geophysical techniques and incorporates a priori geochemical information. Here, we present results from the application of LitMod to the Australian continent. The rasters summarise the results and performance of a Markov-chain Monte Carlo sampling from the posterior model space. Release FR23 is developed using primary-mode Rayleigh phase velocity grids adapted from Fishwick & Rawlinson (2012).</div><div><br></div><div>Geoscience Australia's Exploring for the Future program provides precompetitive information to inform decision-making by government, community and industry on the sustainable development of Australia's mineral, energy and groundwater resources. By gathering, analysing and interpreting new and existing precompetitive geoscience data and knowledge, we are building a national picture of Australia's geology and resource potential. This leads to a strong economy, resilient society and sustainable environment for the benefit of all Australians. This includes supporting Australia's transition to a low emissions economy, strong resources and agriculture sectors, and economic opportunities and social benefits for Australia's regional and remote communities. The Exploring for the Future program, which commenced in 2016, is an eight year, $225m investment by the Australian Government.</div>

<div><strong>Output Type: </strong>Exploring for the Future Extended Abstract</div><div><br></div><div><strong>Short Abstract: </strong>The thickness and thermal structure of continental lithosphere influences the location of seismic and volcanic hazards and is important for predicting long-term evolution of landscapes, sedimentary basins, and the distribution of natural resources. In this project, we have developed new, continental-scale models of the thermomechanical structure of the Australian plate. We begin by compiling an inventory of >15,000 geochemical analyses of peridotitic xenoliths and xenocrysts from across the continent that have been carried up to the surface in volcanic eruptions. We apply thermobarometric techniques to constrain their pressure and temperature of equilibration and perform steady-state heat flow modelling to assess the paleogeotherm beneath these sites. We subsequently use the paleogeotherms as constraints in a Bayesian calibration of anelasticity at seismic frequencies to provide a mapping between seismic velocity and temperature as a function of pressure. We apply this method to several regional-scale seismic tomography models, allowing the temperature to be continuously mapped throughout the Australian lithospheric and asthenospheric mantle. Our models include assessment of uncertainties and can be used to query thermomechanical properties, such as lithospheric thickness, heat flow through the Moho, and the Curie depth.</div><div><br></div><div><strong>Citation: </strong>Hoggard, M.J., Hazzard, J., Sudholz, Z., Richards, F., Duvernay, T., Austermann, J., Jaques, A.L., Yaxley, G., Czarnota, K. & Haynes, M., 2024. Thermochemical models of the Australian plate. In: Czarnota, K. (ed.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra. https://doi.org/10.26186/149411</div>