<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>

<div>The Central Australian Basins 2D Seismic Reprocessing Project is an initiative under Geoscience Australia's "Australia’s Future Energy Resources" (AFER) program, funded by the Australian Government through the "Exploring for the Future" (EFTF) program. The project aims to assess the untapped resource potential of selected underexplored onshore sedimentary basins in terms of natural gas, oil, and groundwater, while also investigating opportunities for geological storage of carbon dioxide and hydrogen. By providing pre-competitive data, the initiative seeks to stimulate investment in mineral, energy, and groundwater exploration.</div><div>&nbsp;</div><div>This project focuses on improving the understanding of the geological evolution and relationships among various Australian basins, ranging from the early Paleozoic Amadeus, Warburton and Adavale basins to the Permian-Triassic Pedirka, Simpson, northern Cooper and southern Galilee basins, and the Jurassic–Cretaceous western Eromanga Basin. To achieve this, modern seismic processing techniques were applied to 33 selected multi-vintage legacy lines with a total length of approximately 2,100 km, enhancing the resolution and image quality of the seismic lines. The dataset includes deep crustal as well as shallow lines from Queensland and South Australia. The data were collected using various acquisition sources such as Vibroseis, Geoflex, and dynamite. Six merged lines were also created to aid in interpretation.</div><div>&nbsp;</div><div>Both stacks and gather data are provided in SEG-Y format, along with navigation data, velocity, and statics. The reprocessing focused on enhancing seismic reflectors and faults, attenuating noise, and optimising frequency content for target depths. Techniques used in the reprocessing include creating a 3D static model, noise attenuation methods, minimum phasing of the Vibroseis data to match dynamite lines, surface-consistent deconvolution, and building a precise velocity model for optimising pre-stack time and depth migration.</div><div><br></div><div><strong>Processed gather data&nbsp;for this survey are also available on request from clientservices@ga.gov.au - Quote eCat# 148931</strong></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.&nbsp;&nbsp;Exploring for the Future program, which commenced in 2016, is an eight year, $225m investment by the Australian Government.</div><div><br></div><div>The Proterozoic Birrindudu Basin is an underexplored region that contains sparse geological data. Strata of similar age are highly prospective to the east, in the McArthur and South Nicholson basins and the Mount Isa region. To investigate this underexplored and data-poor region, the L214 Northwest Northern Territory Seismic Survey was acquired in August to September 2023 by GA and co-funded by the Northern Territory Government. Prior to this survey the region contained minimal seismic data. To complement the acquisition of the seismic survey, a sampling program of legacy stratigraphic and mineral exploration drill holes was also undertaken.</div><div><br></div><div>The new sampling program and seismic reflection data acquired over the Birrindudu Basin and its flanks, has identified many areas of exploration opportunity. This has almost tripled seismic coverage over the Birrindudu Basin, which has enabled new perspectives to be gained on its geology and relationship to surrounding regions. The new seismic has shown an increase in the extent of the Birrindudu Basin, revealing the presence of extensive concealed Birrindudu Basin sedimentary sequences and major, well preserved depocentres. In the central Birrindudu Basin and Tanami Region, shallow basement and deep-seated faults are encouraging for mineralisation, as these structures have the potential to focus mineralised fluids to the near surface. The clear presence of shallow Tanami Region rocks underlying the southern Birrindudu Basin sequences at the northern end of line 23GA-NT2 extends the mineral resource potential of the Tanami Region further north into the southern Birrindudu Basin. A new minimum age of 1822±7 Ma for the deposition of metasediments in drill hole LBD2 for rocks underlying the central Birrindudu Basin, extends the age-equivalent mineral-rich basement rocks of the Tanami Region north into the central Birrindudu Basin – extending the mineral resource potential into a new region.</div><div><br></div><div>The continuous stratigraphy imaged of the Birrindudu Basin by the new seismic is encouraging for energy prospectivity, as the system elements needed for an effective petroleum system, better defined by the new sampling program results, have been imaged to extend over a wider and deeper area. New organic petrological analysis and reflectance data indicate the sampled sections have reached thermal maturity suitable for hydrocarbon generation. Oil inclusion analyses provide evidence for oil generation and migration, and hence elements of a petroleum system are present in the central and northwestern Birrindudu Basin. With the expanded breadth of these rocks demonstrated on the seismic, this greatly increases the spatial extent of hydrocarbon prospectivity in Birrindudu Basin.</div>

<div>Raster datasets of inferred magnesium number for the bulk lithospheric mantle across the Australian continent. The magnesium number is an elemental ratio, defined by Mg / (Mg + Fe), which correlates to the relative enrichment or depletion in incompatible elements. Oxide concentrations are inferred in from thermo-chemical inverse modelling of Rayleigh phase velocities, surface heat flow, geoid anomalies, and topography. The magnesium number rasters summarise the results of a Markov-chain Monte Carlo sampling of the posterior model space from an ensemble of plausible candidate models. Model release 'FR23' is developed using primary-mode Rayleigh phase velocity grids adapted from Fishwick & Rawlinson (2012; "3-D structure of the Australian lithosphere from evolving seismic datasets"). Model release 'KY22' is developed using the primary-mode Rayleigh phase velocity grids of Yoshizawa (2014; "Radially anisotropic 3-D shear wave structure of the Australian lithosphere and asthenosphere from multi-mode surface waves"). All models are products of the Exploring for the Future program.</div>

<div><strong>Output type: </strong>Exploring for the Future Extended Abstract</div><div><br></div><div><strong>Short abstract: </strong> Crustal architecture provides first order controls on the distribution of mineral resources of an area and is best imaged by deep seismic reflection data. Here we present a first interpretation of seismic line 22GA-CD2, acquired as part of the Darling-Curnamona-Delamerian (DCD) project. Line 22GA-CD2 images the central eastern Delamerian Orogen, where basement rocks are concealed by the Murray Basin. Key findings include: (i) the crustal architecture preserves many characteristics of the early evolution of west-dipping Delamerian subduction, accretion and orogeny between ~ 515 Ma - 495 Ma. This initial configuration has been reworked and reactivated during younger orogenic events; (ii) the lower and middle crust constitutes the newly defined Barrier Seismic Province, which is also imaged in legacy seismic reflection line 05GA-TL1 and interpreted to continue northeast to the Olepoloko Fault; (iii) a similar seismic character to that of the Barrier Seismic Province has been observed in legacy seismic reflection lines in Victoria and related to a Cambrian accretionary setting and adjacent foreland; (iv) the present-day upper crustal configuration is largely the result of contractional fault reactivation, with significant vertical movements during the Kanimblan-Alice Springs Orogeny (~ 360 Ma - 340 Ma); (v) a large area of prospective rocks for mineral deposits with Cambrian arc-affiliation are accessible to exploration under shallow cover of the Murray Basin (often less than 200 m).</div><div>&nbsp;&nbsp;</div><div><strong>Citation: </strong>Doublier M.P., et al., 2024. Crustal architecture along seismic line 22GA-CD2: new insights from the Darling-Curnamona-Delamerian deep seismic reflection survey. In: Czarnota, K. (ed.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, https://dx.doi.org/10.26186/149658</div>

<div>One of the key challenges in assessing earthquake hazard in Australia is understanding the attenuation of ground-motion through the stable continental crust. There are now a small number of ground-motion models (GMMs) that have been developed specifically to estimate ground-motions from Australian earthquakes. These GMMs, in addition to models developed outside Australia, are considered here for use in the updated national seismic hazard assessment of Australia. An updated and extended suite of ground-motion data from small-to-moderate Australian earthquakes are used to assess the suitability of the candidate models for use in the Australian context. Recorded spectral intensities are compared with those predicted by the GMMs. Both qualitative and quantitative approaches are considered for such comparisons. The goodness-of-fit results vary significantly among different GMMs, spectral periods and distance ranges; however, overall, the Australian-specific GMMs seem to perform reasonably well in estimating the level of ground shaking for earthquakes in Australia. This paper was presented to the 2022 Australian Earthquake Engineering Society (AEES) Conference 24-25 November (https://aees.org.au/aees-conference-2022/)

<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

The L210 South Nicholson 1096 km-long deep seismic reflection lines were acquired from 6 June to 14 August, 2017. The survey involved the acquisition of seismic reflection and gravity data along five traverses, 17GA-SN1 (375 km), 17GA-SN2 (213 km), 17GA-SN3 (58 km), 17GA-SN3 (98 km), and 17GA-SN5 (352 km). The South Nicholson seismic survey was undertaken in collaboration with and funded by: The energy theme in Geoscience Australia - Exploring for the Future; Northern Territory Geological Survey (NTGS); Department of Natural Resources and Mines - through the Geological Survey of Queensland (GSQ); and AuScope. <b>Raw data for this survey are available on request from clientservices@ga.gov.au - Quote eCat# 116881</b>

<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>

<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 KY22 is developed using the primary-mode Rayleigh phase velocity grids of Yoshizawa (2014).</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>