Critical tests of vertical vs. horizontal tectonic models for the Archaean East Pilbara Granite-Greenstone Terrane, Pilbara Craton, Western Australia

Models for the formation of the high-amplitude (minimum 15 km), long wavelength (120 km) granitoid dome-and-greenstone syncline geometry of the Archaean East Pilbara Granite-Greenstone Terrane (EP) of the Pilbara Craton are controversial. Diapiric models ascribe most structural features to vertical re-organisation of an inverted crustal density profile created by autochthonous magmatic processes during punctuated episodes of partial convective overturn of the upper and middle crust. Alternatively, uniformitarian models interpret the granitoid-cored domes as oversteepened metamorphic core complexes (MCCs) that formed during periods of active extension between periods of regional Alpine-style thrusting. A review of recent advances in lithostratigraphy and geochronology in the EP shows that the greenstone belts are composed everywhere of a coherent, upward-younging stratigraphy, thereby precluding significant thrusting in the formation of the density inversion that drove partial convective overturn. We present new geological evidence that the domes contain some, or all, of the predictive characteristic features of diapirs, including; chaotic internal geometries of domes with otherwise simple outlines, ring faults along dome margins and in flanking greenstone belts, mushroom-shaped fold flaps around the margins of some domes, and sedimentation in inter-diapir synclines. These data, combined with a thorough review of previously proposed core complex models, show that horizontal tectonic models are inadequate to explain the structural, geometric, geochronological, and metamorphic features of the EP. Rather, an integrated model of punctuated partial convective overturn of the upper and middle crust in response to dominantly magmatic processes is presented to explain the ca. 750 Myr history of the terrane. Crown