<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>

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/)