The Capricorn Orogen, central to the West Australian Craton (WAC) and flanked by the Pilbara Craton to the north and the Yilgarn Craton to the south, records complex tectonic processes spanning from the Archean to the Neoproterozoic, including two major Paleoproterozoic collisions—the 2,215–2,145 Ma Ophthalmia Orogeny and the 2,005–1,950 Ma Glenburgh Orogeny—that welded the two cratons. Using finite‐frequency tomography, we present the first high‐resolution P wave velocity model of the upper mantle beneath this region, providing new constraints on cratonic architecture and tectonic evolution. Our results reveal high‐velocity anomalies beneath the Pilbara and Yilgarn Cratons, extending to depths of ∼150–200 km, indicative of thick cratonic keels. The northern edge of the Yilgarn Craton trends northeast, likely extending beneath sedimentary basins to connect with the Pilbara Craton. Its eastern surface trace aligns with the Goodin Fault, while its western margin lies south of the Narryer Terrane, a component of the northwest Yilgarn Craton, suggesting that southward translation of this terrane occurred during the Glenburgh and Capricorn Orogenies. The southern edge of the Pilbara Craton, marked by the Talga Fault, appears structurally diffuse, possibly reflecting its passive margin origins prior to collision. Low‐ (<−0.5%) velocity anomalies within the Capricorn Orogen suggest extensive mantle metasomatism, likely associated with subduction‐driven hydration during the Ophthalmia and Glenburgh Orogenies. These findings provide new insights into the long‐term stabilization and reworking of Archean lithosphere, underscoring the significance of early Paleoproterozoic orogenesis in shaping the deep structure of cratonic regions.

The base of the ICS (International Commission on Stratigraphy) Geological Time Scale was ratified in 2022 by defining a new Global Stratigraphic Standard Age (GSSA) for the lower boundary of the Hadean Eon (formerly 4000-3600 Ma); the age of the Solar System based on the oldest solids, calcium-aluminium inclusions (CAIs), generated in the protoplanetary disk. The formal GSSA for the Hadean base is the oldest reliable, weighted mean Ucorrected Pb-Pb age of 4567.30 +/- 0.16 Ma obtained for CAIs in primitive meteorites Allende and Efremovka. This age is supported by the 4568-4567 Ma U-corrected Pb- Pb ages of chondrules in Northwest African meteorites. The boundary sets an upper lifetime for the protoplanetary disk and timing of planet formation. The Hadean Eon encloses the accretion and differentiation of the Earth and other planets, the Moon-forming Giant Impact, the beginning of the suggested Late Heavy Bombardment, and the formation of the Earths' protocrust. Due to the Moon- forming Giant Impact that occurred after the differentiation of the proto-Earth and the fact that Earth's ' s first crust has been destroyed, the age of the planet Earth itself remains an open question. However, many pieces of astronomical, chemical, physical, and chronological evidence point to the very fast formation of the Solar System and rapid accretion and differentiation of the proto-Earth in only a few million years. Compared to the half-billion-year duration of the Hadean, it is reasonable to set the age of the Earth at the beginning of the formation of the Solar System. This communication explains and justifies the selection of the GSSA for the Hadean base.

In late 2022, the Geological Survey of Western Australia commenced the deployment of a new 10 yr seismic imaging array, Western Australia (WA) array. With the geological history of WA stretching from the Archean to the present, WA array is a natural platform for the study of lithospheric structures pre- and post-establishment of the modern plate tectonics. Despite being a stable craton, certain parts of WA have high seismic activity. This large-scale initiative will map areas of seismic risk for industrial infrastructure and future land use planning and investigate its relationship with the crustal and lithospheric mantle structures using a variety of methods. An economic objective is to identify prospective regions for mineral and energy exploration, especially in areas that have previously been underexplored or for new commodities such as hydrogen. The WA array imaging program will cover the whole State, more than 2.5 million square kilometers, using a grid station spacing of 40 km. The data acquisition is predicted to take 10 yr during which time 1600 stations will be deployed. It is anticipated that this will become one of the largest passive seismic investigations yet instigated. Here, we present and discuss the array design, current deployment status, initial modeling results, expected model updates, and potential implications for the program.

Lead isotopic data imply that thorium and uranium were fractionated from one another in Earth's early history; however, the origin of this fractionation is poorly understood. We report new in situ Pb isotope data from orthoclase in 144 granites sampled across the Archean Yilgarn craton (Western Australia) to characterize its Pb isotope variability and evolution. Granite Pb isotope compositions reveal three Pb sources, a mantle-derived Pb reservoir and two crustal Pb reservoirs, distinguished by their implied source 232Th/238U (kappa Pb). High-kappa Pb granites reflect sources with high 232Th/238U (similar to 4.7) and are largely co-located with Eoarchean- Paleoarchean crust. The Pb isotope compositions of most granites, and those of volcanic hosted massive sulfide (VHMS) and gold ores, define a mixing array between a mantle source and a Th-rich Eoarchean-Paleoarchean source. Pb isotope modeling indicates that the high-kappa Pb source rocks experienced Th/U fractionation at ca. 3.3 Ga. As Th/U fractionation in the Yilgarn craton must have occurred before Earth's atmosphere was oxygenated, subaerial weathering cannot explain the apparent differences in their geochemical behavior. Instead, the high Th/U source reflects Eoarchean-Paleoarchean rocks that experienced prior high-temperature metamorphism, partial melting, and melt loss in the presence of Th-sequestering mineral like monazite. Archean Pb isotope variability thus has its origins in open-system high-temperature metamorphic processes responsible for the differentiation and stabilization of Earth's continental crust.

&lt;p&gt;The Government of Western Australia, through the Geological Survey of Western Australia, is funding a passive seismic acquisition&amp;#160; program, WA array, which has been designed to map Earth&amp;#8217;s lithosphere at an optimal level of station spacing across the state of WA (over 2.5 million square kilometres).&lt;/p&gt; &lt;p&gt;The program, which started on 1 July 2022 will involve the deployment of an &amp;#8220;array&amp;#8221; of 165 seismometers arranged in a grid pattern spaced at 40 kilometre intervals, moving progressively across the state over a period of ten years. Instruments will be relocated on an annual basis across nine regional areas.&lt;/p&gt; &lt;p&gt;It is primarily designed to investigate the crustal and lithospheric mantle structure with the aim of identifying prospective regions for mineral exploration, especially in areas undercover. At the continental scale, the large lithospheric models will target the bulk lithospheric velocities and upper mantle discontinuities, which will provide direct information to better constrain tectonic deformation processes that operated through time. From the Archean nuclei to the Phanerozoic passive margins, WA is composed of many domains with a rich tectonic history; thus WA array will also provide an unprecedented opportunity to study lithospheric structure related to early Earth tectonics, Earth evolution and the Earth today.&lt;/p&gt; &lt;p&gt;The results of the program will step change in our understanding of Western Australia&amp;#8217;s lithospheric architecture. This knowledge will provide a sound scientific basis for mineral and energy exploration, but also for evaluating crucial land use decisions over the coming decades, at a time when large areas of the State are expected to accommodate renewable energy projects.&lt;/p&gt; &lt;p&gt;In addition, the data will be used to evaluate the risks from seismic events, which would contribute to risk assessments for the placement industrial infrastructure such as pipelines and hydrogen generation and storage installations as well as building codes for housing and other buildings.&lt;/p&gt; &lt;p&gt;The first deployment of stations is now in the ground with 158 stations currently running. The first results and raw data will become available at the end of 2024. We will present and discuss the design of the array, initial modelling status and model updates, and related program applications.&lt;/p&gt;

The formation of stable buoyant continental crust during the Archaean Eon was fundamental in establishing the planet's geochemical reservoirs. However, the processes that created Earth's first continents and the timescales over which they formed are debated. Here, we report the Pb isotope compositions of K-feldspar grains from 52 Paleoarchaean to Neoarchaean granites from the Pilbara Craton in Western Australia, one of the world's oldest and best-preserved granite-greenstone terranes. The Pb isotope composition of the Pilbara K-feldspars is variable, implying the granites were derived from crustal precursors of different age and/or variable time-integrated U-238/Pb-204 and Th-232/Pb-204 compositions. Trends to sub-mantle (PbPb)-Pb-207-Pb-/206 ratios preclude the influence of 4.3 Ga crustal precursors. In order to estimate crustal residence times we derive equations to calculate source model ages in a linearized Pb isotope evolution system. The best agreement between the feldspar Pb two-stage source model ages and those derived from zircon initial Hf isotope compositions requires crustal precursors that separated from a chondritic mantle source between 3.2 and 3.8 Ga, and rapidly differentiated to continental crust with U-238/Pb-204 and Th-232/U-238 ratios of similar to 14 and 4.2-4.5, respectively. The preservation of Pb isotope variability in the Pilbara Paleoarchaean granites indicates their early continental source rocks were preserved for up to 500 Ma after their formation. The apparent longevity of these early continental nuclei is consistent with the incipient development of buoyant melt-depleted cratonic lithosphere during the Eoarchaean to Paleoarchaean. Crown Copyright (C) 2021 Published by Elsevier B.V.

The Proterozoic assembly of Australia, the understanding of which is critical for reconstructing Proterozoic supercontinents, involved amalgamation of the West Australian (WAC), North Australian (NAC), and South Australian cratons (SAC). However, the basement between these Archean to early Proterozoic lithospheric blocks is mostly buried beneath younger basins; hence, its composition and age and the timing of Proterozoic assembly remain uncertain. In situ zircon U-Pb-O-Hf analyses of igneous rocks from drillholes that intersected basement beneath the northwestern Canning Basin reveal the presence of a substantial domain of juvenile Proterozoic lithosphere, the Percival Lakes province, between the WAC and NAC. Although isotopically distinct from the neighboring WAC and NAC, the Percival Lakes province is strikingly similar to other juvenile Proterozoic tectonic elements between the WAC, NAC, and SAC. Combining isotope and seismic data, we interpret the Percival Lakes province as part of an ~1700 × 400 km Proterozoic lithospheric domain that lacks evidence of Archean provenance but consists mainly of reworked remnants of Mesoproterozoic oceanic crust that survived WAC-NAC-SAC convergence. The apparent absence of Archean lithosphere between the cratons implies they never directly collided or that complete collision was prevented by impingement of three-dimensional promontories in the converging lithospheric blocks. Instead, the Percival Lakes province and other Proterozoic elements between the WAC, NAC, and SAC consist of oceanic lithosphere extracted from Earth's mantle in the Proterozoic. Our results imply that WAC-NAC convergence was younger than Columbia amalgamation at ca. 1.8 Ga and that Proterozoic Australia formed during the earliest phases of Rodinia assembly at ca. 1.3 Ga.

The isotopic composition of Pb in a mineral or rock at the moment it formed – often referred to as common Pb – provides an important tool to track geological processes through time and space. There is a wide range of applications of common Pb isotopes including understanding magma sources, melt production, fractionation, contamination, and crystallization in the crust. Pb but not U is incorporated into the structure of K-feldspar during crystal growth, which, together with its widespread occurrence as a framework mineral, makes it an excellent common Pb tracer. Consequently, common Pb isotopes in granite K-feldspar crystals provide a potential signature of source composition and a link to crustal growth processes in the mid to lower crust. Hence, combining common Pb isotopes with Sm-Nd (or Lu-Hf) isotopic signatures from the same dated rocks allows assessment of the degree of isotopic communication from deep fractionation systems to those higher in the crustal column. In this contribution, we analyze common Pb isotopic signatures in K-feldspar from a granite sample transect through the Archean Yilgarn Craton in Western Australia. This transect crosses the major crustal-scale Ida Fault that is apparent on Nd and Hf isotopic maps and interpreted as a fundamental lithospheric boundary across which magma sources change. Our results yield a difference in median values of the Pb isotope derivative parameters µ (238U/204Pb) and ω (232Th/204Pb) across the Ida Fault, with higher µ and ω associated with more evolved Nd and Hf isotopic signatures on the western side of the fault. Pb evolution in the Yilgarn Craton is distinct from the widely applied Stacey & Kramers (1975) model. New Yilgarn-specific Pb evolution models are developed with implication for common Pb correction. A correlation in the spatial trends of granite K-feldspar common Pb signatures with those of upper crustal Pb ores and also the Sm-Nd and Lu-Hf systems reveals geochemical communication all the way through the crustal column, implying a common source for the entire lithospheric section on each side of the Ida Fault. Pb isotopes in granite K-feldspar are not an independent geochronometer but may yield important source context on major phase silicate growth that helps refine U-Pb geochronology interpretations (e.g., distinguishing magmatic versus metamorphic zircon growth).

The transition from the Archean to the Proterozoic Eon heralded profound changes in global-scale geological processes, culminating in the emergence of an oxygenated atmosphere on Earth. These changes to the Earth system were driven and enhanced through the Proterozoic by the constant reorganization of the continents into global-scale land masses known as supercontinents. The Proterozoic geological history of Australia provides an almost unbroken record of these global-scale changes and chronicles numerous supercontinent cycles. The present-day Australian continent is comprised of three principle Archean components, or "cratons," namely the West, North and South Australian Cratons, that were stabilized and sutured together at various times throughout the Proterozoic.

Much of the current volume of Earth’s continental crust had formed by the end of the Archaean eon 1 (2.5 billion years ago), through melting of hydrated basaltic rocks at depths of approximately 25–50 kilometres, forming sodic granites of the tonalite–trondhjemite–granodiorite (TTG) suite 2 – 6 . However, the geodynamic setting and processes involved are debated, with fundamental questions arising, such as how and from where the required water was added to deep-crustal TTG source regions 7 , 8 . In addition, there have been no reports of voluminous, homogeneous, basaltic sequences in preserved Archaean crust that are enriched enough in incompatible trace elements to be viable TTG sources 5 , 9 . Here we use variations in the oxygen isotope composition of zircon, coupled with whole-rock geochemistry, to identify two distinct groups of TTG. Strongly sodic TTGs represent the most-primitive magmas and contain zircon with oxygen isotope compositions that reflect source rocks that had been hydrated by primordial mantle-derived water. These primitive TTGs do not require a source highly enriched in incompatible trace elements, as ‘average’ TTG does. By contrast, less sodic ‘evolved’ TTGs require a source that is enriched in both water derived from the hydrosphere and also incompatible trace elements, which are linked to the introduction of hydrated magmas (sanukitoids) formed by melting of metasomatized mantle lithosphere. By concentrating on data from the Palaeoarchaean crust of the Pilbara Craton, we can discount a subduction setting 6 , 10 – 13 , and instead propose that hydrated and enriched near-surface basaltic rocks were introduced into the mantle through density-driven convective overturn of the crust. These results remove many of the paradoxical impediments to understanding early continental crust formation. Our work suggests that sufficient primordial water was already present in Earth’s early mafic crust to produce the primitive nuclei of the continents, with additional hydrated sources created through dynamic processes that are unique to the early Earth.

Isotope maps are used to characterize lithospheric architecture through time, to understand crustal evolution and mineral system distributions, and play an increasingly important role in exploration targeting. These Sm-Nd isotope maps of Western Australia (Fig. 1) are based on whole-rock Sm-Nd data for felsic igneous rocks, which provide a window into the middle and lower continental crust, and are used for isotope mapping. Although mafic to intermediate igneous and sedimentary rocks were not used in constructing the contoured isotope maps, Sm-Nd data for those samples are included with those for felsic igneous rocks in the data table.

The timing and distribution of gold mineralization in Proterozoic orogens is influenced by crustal architecture which is often established long before gold mineralization occurs. Gold occurrences in such settings are commonly associated with crustal-scale faults formed at cratonic margins. Once established, these faults provide critical pathways for hydrothermal and mineralizing fluids which during repeated fault reactivations can result in remobilization or introduction of new auriferous fluids resulting in overprinting gold events. Recently published geochronological data for the northern part of the Proterozoic Capricorn Orogen in Western Australia show it has experienced at least three episodes of gold mineralization occurring at c. 2400, 1770 and 1680 Ma. This information, combined with new data directly linking the timing of hydrothermal activity, gold mineralization and fault reactivation show that the crustal-scale Nanjilgardy and Baring Downs Faults, and their subsidiary structures, were (re)activated during discrete orogenic events. Many of the gold deposits are associated with intracratonic reworking during the 1820-1770 Ma Capricorn Orogeny and 1680-1620 Ma Mangaroon Orogeny. Intracratonic settings are not normally considered prospective for gold mineralization due to a lack of input of juvenile material. However, it appears that repeated hydrothermal fluid flow during intracratonic events, has the potential to upgrade gold mineralization or increase gold endowment throughout the orogen, either through gold remobilization or through introduction of new gold, increasing the potential for economic gold deposits.

SummaryThe timing and distribution of gold mineralization in Proterozoic orogens is influenced by crustal architecture which is often established long before gold mineralization occurs. Gold occurrences in such settings are commonly associated with crustal-scale faults formed at cratonic margins. Once established, these faults provide critical pathways for hydrothermal and mineralizing fluids which during repeated fault reactivations can result in remobilization or introduction of new auriferous fluids resulting in overprinting gold events. Recently published geochronological data for the northern part of the Proterozoic Capricorn Orogen in Western Australia show it has experienced at least three episodes of gold mineralization occurring at c. 2400, 1770 and 1680 Ma. Many of the gold deposits are associated with intracratonic reworking during the 1820–1770 Ma Capricorn Orogeny and 1680–1620 Ma Mangaroon Orogeny. Intracratonic settings are not normally considered prospective for gold mineralization due to a lack of input of juvenile material. However, it appears that repeated hydrothermal fluid flow during intracratonic events, has the potential to upgrade gold mineralization or increase gold endowment throughout the orogen, either through gold remobilization or through introduction of new gold, increasing the potential for economic gold deposits.

Summary State- and federal-generated pre-competitive geoscience data is critical for exploration success. These relatively low-cost but high-quality regional-scale datasets ultimately reduce the financial risk to explorers by reducing the search space and allowing a more targeted use of exploration expenditure. In Western Australia, over 20 years of geological mapping and associated research in the Capricorn Orogen has led to a robust understanding of the orogen architecture and its temporal and thermal evolution. Recent in situ geochronology work in the northern part of the orogen, has bridged the gap between prospect-scale ‘exploration’ geoscience data with regional- and province-scale data, ultimately leading to a better understanding of the regional-scale drivers and pathways for gold mineralization in this part of the orogen. This information is critical for exploration models as it opens up older parts of the northern Capricorn basins that were traditionally considered unprospective, and refines and focusses exploration strategies to target the major crustal structures and their ancillary structures.

Proterozoic orogens commonly host a range of hydrothermal ores that form in diverse tectonic settings at different times. However, the link between mineralization and the regional-scale tectonothermal evolution of orogens is usually not well understood, especially in areas subject to multiple hydrothermal events. Regional-scale drivers for mineral systems vary between the different classes of hydrothermal ore, but all involve an energy source and a fluid pathway to focus mineralizing fluids into the upper crust. The Mount Olympus gold deposit in the Proterozoic Capricorn Orogen of Western Australia, was regarded as an orogenic gold deposit that formed at ca. 1738 Ma during the assembly of Proterozoic Australia. However, the trace element chemistry of the pyrite crystals closely resembles those of the Carlin deposits of Nevada, with rims that display solid solution gold accompanied by elevated As, Cu, Sb, Hg, and TI, surrounding gold-poor cores. New SHRIMP U-Pb dating of xenotime intergrown with auriferous pyrite and ore-stage alteration minerals provided a weighted mean (207)pb*/(206)pb* date of 1769 +/- 5 Ma, interpreted as the age of gold mineralization. This was followed by two discrete episodes of hydrothermal alteration at 1727 +/- 7 Ma and 1673 +/- 8 Ma. The three ages are linked to multiple reactivation of the crustal-scale Nanjilgardy Fault during repeated episodes of intracratonic reworking. The regional-scale drivers for Carlin-like gold mineralization at Mount Olympus are related to a change in tectonic regime during the final stages of the intracratonic 1820-1770 Ma Capricorn Orogeny. Our results suggest that substantial sized Carlin-like gold deposits can form in an intracratonic setting during regional-scale crustal reworking. (C) 2018, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.