Conductive incubation and the origin of dome-and-keel structure in Archean granite-greenstone terrains: A model based on the eastern Pilbara Craton, Western Australia

The Archean East Pilbara Granite-Greenstone Terrane (EPGGT) of the Pilbara Craton in Western Australia preserves a prolonged record of voluminous mafic-dominated volcanism and felsic plutonism, commencing at circa 3515 Ma and ultimately resulting in the development of spectacular "dome-and-keel" structures. Early crustal growth was dominated by basaltic magmatism and the regional development of a 12-18 km thick greenstone sequence by circa 3335 Ma, overlying widespread 3470-3430 Ma tonalite-trondhjemite-granodiorite (TTG) suites emplaced into the middle crust. Stratigraphic and structural relationships imply that voluminous granitoid plutonism and crustal-scale dome-and-keel formation in the southeastern EPGGT was not initiated until circa 3325 Ma but proceeded rapidly over the interval 3325-3308 Ma. This scenario is consistent with a "conductive incubation" period of 10-100 Myr duration, following the burial of radiogenic granitic crust beneath the accumulated greenstone pile. For heat production parameters appropriate to the 3515-3308 Ma EPGGT, we show that the burial of 3470-3430 Ma granitoid-rich crust beneath the greater than or equal to3335 Ma Euro Basalt and its precursors led to long-term crustal temperature increases of 170 234degreesC at 35 km depth, with a corresponding reduction in effective viscosity of 2-5 orders of magnitude. In combination with the greenstone-over-granitoid density inversion, the changes in effective viscosity of the mid to deep crust due to the burial of heat sources may have provided the crucial trigger for the initiation of dome-and-keel formation. Similarly, cooling and strengthening of the crust during syndoming exhumation of the heat production potentially terminated large-scale dome-and-keel amplification.