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Martin Van Kranendonk, Geological Survey of Western Australia (Australia)
David Huston, Geoscience Australia (Australia)
Arthur Hickman, Geological Survey of Western Australia (Australia)
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The Archean Pilbara Craton contains five geologically distinct terranes that evolved over ∼800 My. The 3.53-3.17 Ga East Pilbara Terrane (EPT) represents the ancient nucleus of the craton. It formed from three distinct mantle plume events from 3.53-3.24 Ga that erupted thick, dominantly basaltic volcanic successions on older crust to 3.72 Ga. Heat from plumes caused voluminous mafic-ultramafic magmatism, uplift, and extension of the crust. Each plume event was accompanied by crustal melting that generated early TTG, and then progressively more evolved granitic magmas that were emplaced into the upper crust during periods of partial convective overturn. Mantle melting events caused severe depletion of the subcontinental lithospheric mantle, making the EP a stable, buoyant, unsubductable protocontinent by 3.2 Ga. Associated mineralization includes: syn-volcanic Cu-Zn-Pb-barite VHMS deposits and a hydrothermal barite-Zn-Pb-Cu sedimentary replacement deposit; polymetallic and base metal deposits in felsic porphyries; mesothermal gold deposits in shear zones around granitic domes; and local Cu-Mo porphyry mineralization. Underexplored mineralization styles include komatiite-hosted Ni-deposits in plume volcanics, and Ni-Cu-PGE deposits in EPT rift-margin volcanics.
After 3.2 Ga, horizontal tectonics dominated over vertical tectonics, leading to 3.12 Ga subduction, and 3.07 Ga accretion of the West Pilbara Superterrane (WPS) with the EPT. Komatiites of the 3.27 Ga Karratha Terrane host Ni-Cu mineralization. The 3.12 Ga, 10-km thick Whundo Group (Sholl Terrane) has stratigraphic and geochemical characteristics of modern oceanic arcs (e.g., boninites and evidence for flux melting), including VHMS Cu-Zn mineralization. Terrane accretion and WPS- EPT collision at 3.07 Ga (Prinsep Orogeny) was followed by development of an intracontinental sag basin (3.02?2.93 Ga De Grey Supergroup), and west-to-east prograding granitic plutonism (3.00?2.93 Ga) and compressional deformation (2.95?2.91 Ga). Associated mineralization includes 3.02 Ga banded iron-formation and V-Ti-magnetite in mafic-ultramafic intrusions, 2.97 Ga Cu-Zn VHMS deposits, and 2.95 Ga Ni-Cu-PGE-orthomagmatic Au in mafic-ultramafic sills associated with intrusion of sanukitoids. Orogenic gold deposits formed in 2.95?2.91 Ga thrusts and shear zones across the craton, analogous with Au-mineralized Neoarchean orogens. Late-tectonic ultramafic intrusions (2.92 Ga), emplaced in transtension, host Ni-Cu-PGE. Post-tectonic granites (2.89?2.83 Ga) host Sn-Ta-Li.
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