Review: secular tectonic evolution of Archean continental crust: interplay between horizontal and vertical processes in the formation of the Pilbara Craton, Australia

The Archean Pilbara Craton contains five geologically distinct terranes - the East Pilbara, Karratha, Sholl, Regal and Kurrana Terranes - all of which are unconformably overlain by the 3.02- to 2.93-Ga De Grey Superbasin. The 3.53-3.17 Ga East Pilbara Terrane (EP) represents the ancient nucleus of the craton that formed through three distinct mantle plume events at 3.53-3.43, 3.35-3.29 and 3.27-3.24 Ga. Each plume event resulted in eruption of thick dominantly basaltic volcanic successions on older crust to 3.72 Ga, and melting of crust to generate first tonalite-trondhjemite-granodiorite (TTG), and then progressively more evolved granitic magmas. In each case, plume magmatism was accompanied by uplift and crustal extension. The combination of conductive heating from below, thermal blanketing from above, and internal heating of buried granitoids during these events led to episodes of partial convective overturn of upper and middle crust. These mantle melting events caused severe depletion of the subcontinental lithospheric mantle, making the EP a stable, buoyant, unsubductable continent by c. 3.2 Ga. Extension accompanying the latest event led to rifting of the protocontinent margins at between 3.2 and 3.17 Ga. After 3.2 Ga, horizontal tectonic forces dominated over vertical forces, as revealed by the geology of the three terranes (Karratha, Sholl and Regal) of the West Pilbara Superterrane. The c. 3.12-Ga Whundo Group of the Sholl Terrane is a fault bounded, 10-km-thick volcanic succession with geochemical characteristics of modern oceanic arcs (including boninites and evidence for flux melting) that indicate steep Archean subduction. At 3.07 Ga, the 3.12-Ga Sholl Terrane, 3.27-Ga Karratha Terrane and c. 3.2-Ga Regal Terrane accreted together and onto the EP during the Prinsep Orogeny. This was followed by development of the De Grey Superbasin - an intracontinental sag basin and widespread plutonism (2.99-2.93 Ga) as a result of orogenic relaxation and slab break off. Craton-wide compressional deformation at 2.95-2.93 Ga culminated with 2.91-Ga accretion of the 3.18 Ga Kurrana Terrane with the EP. This compression caused amplification of the dome-and-keel structure in the EP. Final cratonization was effected by emplacement of 2.89-2.83 Ga post-tectonic granites.