Crustal architecture places first-order controls on the distribution of mineral and energy resources. However, despite its importance, it is poorly constrained over much of northern Australia. Here, we present a full crustal interpretation of deep seismic reflection profile 18GA-KB1 that extends over 872 km from the Eo- to Mesoarchean Pilbara Craton to the Paleoproterozoic Aileron Province, transecting a range of stratigraphic and tectonic basement units, some of which are completely concealed by younger rocks. The seismic profile provides the first coherent image through this relatively poorly understood part of Australian geology and yields major new insights about the crustal architecture, geometry and definition of the different geological and seismic provinces and their boundaries. Key findings include the following: (1) The Pilbara Craton shows a three-component horizontal crustal layering, where the granite– greenstone East Pilbara Terrane is largely confined to the upper crust. (2) The Pilbara Craton has an extensive reworked margin, the Warrawagine Seismic Province, that thins towards the east, and underlies the western and central Rudall Province. (3) At the largest scale, the Rudall Province shows an approximately funnel-shaped geometry, with limited differences in seismic character between the various terranes. (4) The western Kidson Sub-basin is underlain by rocks of the Neoproterozoic Yeneena Basin and Rudall Province. (5) The central and eastern part of the Kidson Sub-basin rests on the coherent, relatively poorly structured Punmu Seismic Province, which is truncated by the steep, crustal-scale Lasseter Shear Zone, that marks the boundary to the Aileron Province to the east. <b>Citation:</b> Doublier, M.P., Johnson, S.P., Gessner, K., Howard, H., Chopping, R., Smithies, R.H., Martin, D.McB.,Kelsey, D.E., Haines, P.w., Hickman, A., Czarnota, K., Southby, C., Champion, D.C., Huston, D.L., Calvert, A.J., Kohanpour, F., Moro, P., Costelloe, R., Fomin, T. and Kennett, B.L.N., 2020. Basement architecture from the Pilbara Craton to the Aileron Province: new insights from deep seismic reflection line 18GA-KB1. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.

<div>Archean greenstone belts are a vital window into the tectonostratigraphic processes that operated in the early Earth and the geodynamics that drove them. However, the majority of greenstone belts worldwide are highly-deformed, complicating geodynamic interpretations. The volcano-sedimentary sequence of the 2775-2690 Ma Fortescue Group is different in that it is largely undeformed, offering a unique insight into the architecture of greenstone sequences. In the Fortescue magmatic rocks, geochemical signatures that in deformed belts in the Superior or Yilgarn Cratons might have been interpreted as arc-like, are explained by contamination of rift-related mantle and plume-derived magmas with Pilbara basement crust; understanding the wider geological and structural setting allows a more complete interpretation.</div><div> However, contamination of Fortescue magmas by an enriched sub-continental mantle lithosphere (SCLM) is an alternative hypothesis to the crustal contamination model. If demonstrated, the addition of sediments and fluids to the SCLM, required to form enriched/metasomaytised SCLM, would suggest active subduction prior to the Neoarchean. To test this hypothesis, we collected Hf-O isotopic data on zircons from felsic volcanic rocks throughout the Fortescue Group; if the contamination had a subducted sedimentary component (δ18O>20‰), then the O-isotopes should record a heavy signature.</div><div> The results show that the ca. 2775 Ma Mt Roe Formation has εHfi from 0 to -5.6, and δ18OVSMOW of +4.8- +0.3‰, with the majority of values <+3‰. The ca. 2765 Ma Hardey Formation (mostly sediments) has highly unradiogenic εHfi of -5 to -9.4, and δ18O of +7.8- +6.6‰. The ca. 2730 Ma Boongal Formation displays similar values as for Mt Roe, with εHfi +1.9 to -5.5 and δ18O +3.0 to -0.6‰. The ca. 2720 Ma Tumbiana Formation shows the greatest range in εHfi from +4.9 to -4.6, with δ18O +7.1- +0.7‰, with the majority between +4.5 and +2.5‰. Data from the 2715 Ma Maddina Formation are more restricted, with εHfi between +4.0 and -0.1, and δ18O +5.0- +3.8‰. The youngest formation, the 2680 Ma Jeerinah Formation, has εHfi +2.3 to -6.2, and δ18O +5.1 to -2.1‰.</div><div> Importantly, these data provide little evidence of a cryptic enriched SCLM source in the Fortescue magmas. Furthermore, the dataset contains some of the lightest δ18O data known for Archean zircon, highlighting a ca. 100 Myr period of high-temperature magma-water interaction, with long-term continental emergence implied by the trend to meteoric δ18O compositions. The exception to this is the Hardey Formation, which may have formed via crustal anatexis in a period of reduced heat-flow between the 2775-2665 and 2730-2680 Ma events. Data from the other formations show a broad trend of increasing δ18O and εHf from 2775 to 2680 Ma. We suggest this represents the effects of progressive cratonic rifting, allowing mantle-derived magmas to reach the surface less impeded, and also a decreasing role of meteoric water in the rift zone as the sea invades. As a result, the εHf and δ18O data from the Fortescue Group represent the evolving nature of an Archean rift zone, from an emergent volcanic centre, to a submarine environment.</div><div><br></div>This Abstract was submitted/presented to the 2023 6th International Archean Symposium (6IAS) 25 - 27 July (https://6ias.org/)

The 2.1─1.79 Ga Trans-Australian and Canadian Trans-Hudson orogens preserve a common record of Himalayan-scale orogenesis and voluminous Cordilleran-style magmatism behind which turbidite-dominated sedimentary sequences evolved in a back-arc or retro-arc foreland setting. Successive cycles of subduction retreat and advance drove the orogenic process, culminating in continent-continent collision and closure of a shared and formerly contiguous ocean basin – the Paleoproterozoic Diamantina and Manikewan oceans. Cordilleran-style arc magmatism in proto-Australia commenced along the southern reaches of the Diamantina Ocean with emplacement of the 2005-1975 Ma Dalgaringa batholith along the leading edge of the Pilbara Craton (Gascoyne Province) before both it and its host craton docked against the Yilgarn Craton, resulting in the Glenburgh Orogeny. After a brief episode of post-kinematic granite magmatism from 1965─1945 Ma, tectonic activity switched to the opposing margin of the Diamantina Ocean in what is now northern Australia where a further three cycles of upper plate orogenesis and Cordilleran-style magmatism occurred from 1890─1850 Ma, 1840─1810 Ma and 1810─1760 Ma along a convergent continental margin extending from the Kimberley and Pine Creek regions southward through the Mount Isa domain into the eastern Gawler Craton. Batholiths developed along this margin include granites of both low and high Sr/Y composition with the more adakitic varieties interpreted to have been intruded during periods of enhanced asthenospheric upwelling accompanying the opening of one or more slab windows following slab breakoff, tearing and/or subduction of an actively spreading oceanic ridge. Terminal collision between the North and South Australian (Mawson) cratons at ca. 1790 Ma brought this succession of subduction-related events to a close, although neither this event nor the corresponding Trans-Hudson orogen need equate to final assembly of the Nuna supercontinent. Instead, the 1870 Ma peak in global compilations of magmatic and detrital zircon ages may be more simply interpreted as the result of elevated tectonism and magmatism along a Paleoproterozoic Cordilleran-style continental plate margin that was trans-continental in scale and continued uninterrupted from proto-Australia into northern Canada and beyond. <b>Citation:</b> G.M. Gibson, D.C. Champion, M.P. Doublier; The Paleoproterozoic Trans-Australian Orogen: Its magmatic and tectonothermal record, links to northern Laurentia, and implications for supercontinent assembly. GSA Bulletin 2024; doi: https://doi.org/10.1130/B36255.1

<div>Sander Geophysics Limited (SGL) conducted a fixed-wing high resolution airborne gravimetric survey over two survey blocks, Pilbara Northwest and Pilbara Southeast in Northwestern Australia for Geoscience Australia and its partner the Geological Survey of Western Australia (GSWA). </div><div>The traverse lines were oriented east-west in the Pilbara Northwest block and north-south in the Pilbara Southeast block and spaced at 2500 m. A limited number of control lines flown exclusively in the Pilbara Northwest block were oriented north-south and spaced at 50,000 m. A drape surface was created taking into account the terrain and the performance of the aircraft at the expected altitudes and estimated temperatures. The survey was flown with a target clearance of survey 160m above ground level. </div><div>&nbsp;</div><div><strong>Survey details </strong></div><div>Survey Name: Pilbara WA airborne gravity surveys 2019</div><div>State/Territory: Western Australia (WA)</div><div>Datasets Acquired: Airborne gravity</div><div> Geoscience Australia Project Number: P1314</div><div> Acquisition Start Date: April 23, 2019</div><div> Acquisition End Date: June 16, 2019</div><div> Flight line spacing: 2500m</div><div> Flight line direction: 270deg / EW (Pilbara NW); 180deg / NS (Pilbara SE)</div><div> Control line spacing: 50,000m – Pilbara NW only</div><div> Control line direction: 180 deg / NS – Pilbara NW only</div><div>Total line kilometers: 69,943</div><div> Nominal terrain clearance (above ground level): 160m</div><div> Aircraft type: Cessna Grand Caravan 208B</div><div>Data Acquisition: Sander Geophysics Limited </div><div> Project Management: Geoscience Australia</div><div> Quality Control: Geoscience Australia</div><div> Dataset Ownership: GSWA and Geoscience Australia</div><div>&nbsp;</div><div>This data package release contains the final survey deliverables received from the contractor SGL, and peer reviewed by Dr Mark Dransfield.</div><div>&nbsp;</div><div><strong>1.</strong> <strong><em>Point-located Data / line data</em></strong></div><div>ASCII XYZ and ASEG-GDF2 format with accompanying description and definition files.</div><div><br></div><div><strong><em>2.Grids</em></strong> in General eXchange Format (.gxf) and ERMapper format (.ers)</div><div> Datum:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;GDA94</div><div>Projection:&nbsp;&nbsp;MGA 50</div><div>Grid cell size:&nbsp;500m</div><div>A full wavelength spatial filter of 5000m was applied to all the gravity grids. See details in the readme files.</div><div><br></div><div> <strong>3. Readme files</strong></div><div>- PNW-readme-grav.txt </div><div>- PSE-readme-grav.txt</div><div><br></div><div><strong>4. Reports</strong> </div><div> - Final survey logistic report (Pilbara SE and NW) from the contractor: P1314_Pilbara_2019_TR-878-000.pdf </div><div>- Pilbara NW survey QC report by M Dransfield: Pilbara NW AG QC report.pdf </div><div>- Pilbara SE survey QC report by M Dransfield: Pilbara SE AG QC report.pdf</div><div><br></div><div> The data from this Pilbara survey are also available for download from https://geoview.dmp.wa.gov.au/GeoView under reference number 71470.</div>