<div>In mid-2022 two paleoseismic trenches were excavated across the Willunga Fault at Sellicks Hill, ~40 km south of Adelaide, at a location where range front faulting displaces a thick colluvial apron, and flexure in the hanging wall has produced an extensional graben. Vertical separation between time-equivalent surfaces within the Willunga Embayment and uplifted Myponga Basin indicate an average uplift rate of 40 m/Myr since 5 Ma across the Willunga fault at the trench location, equivalent to a slip rate of 57 m/Myr across a 45° dipping fault. </div><div> The field sites preserve evidence for at least 4-5 large earthquake events involving approximately 6.9 m of discrete slip on fault planes since the Mid to Late Pleistocene. If the formation of red soil marker horizons in the trenches are assumed to relate to glacial climatic conditions then a slip-rate of 26-46 m/Myr since the Mid Pleistocene is obtained. These deformation rate estimates do not include folding in the hanging wall of the fault, which is likely to be significant at this site as evidenced by the existence of a pronounced hanging wall anticline. In the coming months, the results of dating analysis will allow quantitative constraint to be placed on earthquake timing and slip-rate, and a structural geological study seeks to assess the proportion of deformation partitioned into folding of the hanging wall.</div><div> The 2022 trenches represent the most recent of ten excavated across this fault. Integration of the 2022 data with those from previous investigations will allow fundamental questions to be addressed, such as whether the Willunga fault ruptures to its entire length, or in a segmented fashion, and whether any segmentation behaviour is reflected in local slip-rate estimates. Thereby we hope to significantly improve our understanding of the hazard that this, and other proximal Quaternary-active faults, pose to the greater Adelaide conurbation and its attendant infrastructure.</div> This paper was presented to the 2022 Australian Earthquake Engineering Society (AEES) Conference 24-25 November (https://aees.org.au/aees-conference-2022/)

<div><strong>Output type: </strong>Exploring for the Future Extended Abstract </div><div><br></div><div><strong>Short Abstract: </strong>The Delamerian Orogen, with a length of ~1000 km on mainland Australia and a proven potential to host mineralisation, represents an evolving exploration opportunity. However, uncertainty surrounding the age and tectonic setting of the orogen is a barrier to confident exploration in frontier covered regions, such as the Loch Lilly-Kars Belt in western New South Wales and South Australia. A major area of uncertainty is the configuration and extent of the Cambrian convergent-margin system and lateral variations thereof. In this study, we highlight multidisciplinary data from new and legacy sources, including lithology, geochronology, geochemistry, potential-field geophysics, deep-crustal seismic, and magnetotelluric data that permit a revised interpretation of the geological framework for the Delamerian Orogen in mainland Australia, with an emphasis on the covered, central part of the system. These data indicate that a largely continuous, east-facing volcanic arc developed in the Delamerian Orogen in the Cambrian. The arc transitions from exhibiting a strong continental affinity in the Koonenberry Belt to having less continental affinity in the Grampians-Stavely Zone of Victoria. The Loch Lilly-Kars Belt is interpreted to have occupied a volcanic arc to incipient back-arc position in the middle Cambrian.&nbsp;</div><div><br></div><div><strong>Citation: </strong>Clark A.D., et al., 2024. Cambrian convergent margin configuration in the Delamerian Orogen of mainland Australia. In: Czarnota, K. (ed.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, https://doi.org/10.26186/149647 </div>

<div>Geoscience Australia's geoscientific relational databases use look-up tables to describe the data stored within. These look-ups contain, but are not limited to, information about boreholes, field geology, inorganic and organic geochemistry, hydrochemistry, geophysics, rock properties, samples and other general geological terms. These terms have then been compiled into a vocabulary of terms for publication via GA's vocabulary service. Within this vocabulary, GA references where sourced terms are published in external vocabularies with a source vocabulary URI (Uniform Resource Identifier). </div><div><br></div><div>All vocabularies, collections of concepts within vocabularies and individual concepts are identified with URI persistent identifiers of the form:</div><div>http://pid.geoscience.gov.au/def/voc/ga/{VOCABULARY-KEY}/{COLLECTION-OR-CONCEPT-NAME}</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>The active seismic and passive seismic database contains metadata about Australian land seismic surveys acquired by Geoscience Australia and its collaborative partners. </div><div>For active seismic this is onshore surveys with metadata including survey header data, line location and positional information, and the energy source type and parameters used to acquire the seismic line data. For passive seismic this metadata includes information about station name and location, start and end dates, operators and instruments. Each also contains a field that contains links to the published data. </div><div><br></div><div>The active and passive seismic database is a subset of tables within the larger Geophysical Surveys and Datasets Database and development of these databases was completed as part of the second phase of the Exploring for the Future (EFTF) program (2020-2024). The resource is accessible via the Geoscience Australia Portal&nbsp;(https://portal.ga.gov.au/), under 'Geophysics'. Use 'active seismic' or 'passive seismic' as search terms. </div><div><br></div>

<div>The city of Lae is Papua New Guinea (PNG)’s second largest, and is the home of PNG’s largest port. Here, a convergence rate of ~50 mm/yr between the South Bismarck Plate and the Australian Plate is accommodated across the Ramu-Markham Fault Zone (RMFZ). The active structures of the RMFZ are relatively closely spaced to the west of Lae. However, the fault zone bifurcates immediately west of the Lae urban area, with one strand continuing to the east, and a second strand trending southeast through Lae City and connecting to the Markham Trench within the Huon Gulf. </div><div>The geomorphology of the Lae region relates to the interaction between riverine (and limited marine) deposition and erosion, and range-building over low-angle thrust faults of the RMFZ. Flights of river terraces imply repeated tectonic uplift events; dating of these terraces will constrain the timing of past earthquakes and associated recurrence intervals. Terrace riser heights are typically on the order of 3 m, indicating causative earthquake events of greater than magnitude 7. </div><div>Future work will expose the most recently active fault traces in trenches to assess single event displacements, and extend the study to the RMFZ north of Nadzab Airport. These results will inform a seismic hazard and risk assessment for Lae city and surrounding region.</div> Presented at the 2023 Australian Earthquake Engineering Society (AEES) Conference

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>The presence of Pliocene marine sediments in the Myponga and Meadows basins within the Mt Lofty Ranges south of Adelaide is testament to over 200&nbsp;m of tectonic uplift within the last 5 Myr (e.g., Sandiford 2003, Clark 2014). The spatiotemporal distribution of uplift amongst the various faults within the range and along the range fronts is poorly understood. Consequently, large uncertainties are associated with estimates of the hazard that the faults pose to proximal communities and infrastructure.</div><div>&nbsp;</div><div>We present the preliminary results of a paleoseismic investigation of the southern Willunga Fault, ~40 km south of Adelaide. Trenches were excavated across the fault to examine the relationships between fault planes and sedimentary strata. Evidence is preserved for 3-5 ground-rupturing earthquakes since the Middle to Late Pleistocene, with single event displacements of 0.5 – 1.7 m. Dating of samples will provide age constraints on the timing of these earthquakes. This most recent part of the uplift history may then be related to the longer-term landscape evolution evidenced by the uplifted basins, providing an enhanced understanding of the present-day seismic hazard.</div> This abstract was presented at the Australian & NZ Geomorphology Group (ANZGG) Conference in Alice Springs 26-30 September 2022. https://www.anzgg.org/images/ANZGG_2022_First_circular_Final_V3.pdf

<div>In Australia, wide-spread sedimentary basin and regolith cover presents a key challenge to explorers, environmental managers and decision-makers, as it obscures underlying rocks of interest. To address this, a national coverage of airborne electromagnetics (AEM) with a 20&nbsp;km line-spacing is being acquired. This survey is acquired as part of the Exploring for the Future program and in collaboration with state and territory geological surveys. This survey presents an opportunity for regional geological interpretations on the modelled AEM data, helping constrain the characteristics of the near-surface geology beneath the abundant cover, to a depth of up to ~500&nbsp;m.</div><div> The AEM conductivity sections were used to delineate key chronostratigraphic boundaries, e.g. the bases of geological eras, and provide a first-pass interpretation of the subsurface geology. The interpretation was conducted with a high level of data integration with boreholes, potential fields geophysics, seismic, surface geology maps and solid geology maps. This approach led to the construction of well-informed geological interpretations and provided a platform for ongoing quality assurance and quality control of the interpretations and supporting datasets. These interpretations are delivered across various platforms in multidimensional non-proprietary open formats, and have been formatted for direct upload to Geoscience Australia’s (GA) Estimates of Geological and Geophysical Surfaces (EGGS) database, the national repository of multidisciplinary subsurface depth estimates.</div><div> These interpretations have resulted in significant advancements in our understanding of Australia’s near-surface geoscience, by revealing valuable information about the thickness and composition of the extensive cover, as well as the composition, structure and distribution of underlying rocks. Current interpretation coverage is ~110,000 line kilometres of AEM conductivity sections, or an area &gt;2,000,000&nbsp;km2, similar to the area of Greenland or Saudi Arabia. This ongoing work has led to the production of almost 600,000 depth estimate points, each attributed with interpretation-specific metadata. Three-dimensional line work and over 300,000 points are currently available for visualisation, integration and download through the GA Portal, or for download through GA’s eCat electronic catalogue. </div><div> These interpretations demonstrate the benefits of acquiring broadly-spaced AEM surveys. Interpretations derived from these surveys are important in supporting regional environmental management, resource exploration, hazard mapping, and stratigraphic unit certainty quantification. Delivered as precompetitive data, these interpretations provide users in academia, government and industry with a multidisciplinary tool for a wide range of investigations, and as a basis for further geoscientific studies.</div> Abstract submitted and presented at 2023 Australian Earth Science Convention (AESC), Perth WA (https://2023.aegc.com.au/)

<div>Convergent margins are a hallmark feature of modern style plate tectonics. One expression of their operation is metallogenesis, which therefore may yield important insights into secular changes in styles of convergence and subduction. A global comparison of metallogenesis along convergent margins of over 20 well-endowed provinces indicates a consistent and systematic progression of mineral deposit types. We term this progression the convergent margin metallogenic cycle (CMMC). </div><div> This CMMC mirrors convergent margin evolution. Each metallogenic cycle begins with the formation of porphyry copper deposits and/or volcanic-hosted massive sulphide deposits, associated with arc construction and back arc basin formation, respectively. When the convergent margin transitions into contraction/orogenesis due to processes such as accretion, flattening of subduction, or continent-continent collision, mineral deposits that form include orogenic gold and structurally hosted base metal deposits. Post-contractional extension is marked by the formation of intrusion related rare metal (tin, tungsten, molybdenum) and gold deposits, pegmatites, and alkaline porphyry copper deposits, closing the CMMC. </div><div> Our analysis of the metallogenic record reveals that prior to ~3 Ga, metallogenesis is episodic and non-systematic, with CMMCs not recognised. From the mid- to late Mesoarchean onwards, CMMCs are observed in all provinces analysed, and display systematic trends through time: the Meso- to Neoarchean metallogenic provinces are characterized by a single metallogenic cycle, whereas in the Paleo- to Mesoproterozoic provinces, both single and multiple metallogenic cycles occur. From the middle Neoproterozoic onwards multiple metallogenic cycles are the rule. This evolution is accompanied by an increase in the duration of metallogenesis, ranging from ~100 to 180 million years in the Meso- to Neoarchean and 220 to more than 400 million years since the late Proterozoic.&nbsp;</div><div> We interpret these trends to reflect secular changes in tectonic processes and Earth evolution. The emergence of CMMCs from ~3 Ga provides independent evidence for the operation of some early form of subduction since this time. The fact that CMMCs are recognized in all provinces of mid-Meso- to Neoarchean age suggests that subduction was the common <em>modus operandi</em> rather than an exception. The first appearance of multiple metallogenic cycles in the Paleoproterozoic may reflect the strengthening of cratonic margins by tectonothermal maturation since formation in the Archean. Long-lived metallogenesis and multiple metallogenic cycles in the Neoproterozoic and Phanerozoic are linked to deep-slab break-off, or modern, subduction in which the internal strength of the subducting slab allows maintenance of slab coherency.&nbsp;&nbsp;</div><div> This Abstract was submitted/presented to the 2023 6th International Archean Symposium (6IAS) 25 - 27 July (https://6ias.org/)