Archaean orogen-parallel extension: evidence from the northern Eastern Goldfields Province, Yilgarn Craton

Evidence for a previously undocumented stage of extensional deformation in the northern Eastern Goldfields Province (EGP) of the Yilgarn Craton is presented, based on detailed studies of gold deposits in the Laverton region. It is suggested that extension was contemporaneous with, and controlled by, east–west-directed shortening associated with a major orogenic event (D2) that affected all of the EGP. Thermal weakening associated with a major phase of granite emplacement destroyed isostatic equilibrium established during D2 crustal thickening. Extension occurred during late D2, with σ1 being approximately vertical. Tectonic transport was constrained to an approximately NNW–SSE orientation due to the farfield effects of the waning stages of D2. Gold mineralisation in a number of deposits, including the world-class Sunrise and Wallaby gold deposits, shows intimate temporal and spatial relationships with low-dipping structures produced during gravitational collapse. This suggests that the regionally developed, orogenically late stage of gold mineralisation represented across the goldfields was coincident with a complex interplay of both horizontally and vertically-directed contractional deformation.