Late Archaean synorogenic basins of the Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia: Part III. Signatures of tectonic escape in an arc-continent collision zone

Siliciclastic supersequences in the Eastern Goldfields Superterrane are remnants of basins that were linear zones of subsidence between intra-terrane faults. Fluvial deposits record proximal to medial braid-plains. Deep-marine canyon and fan deposits were linked across intra-terrane compartments only by mud-rich deposits. Axial depositional systems dominate, with only minor evidence for slope-aprons, although transverse and axial systems are preserved in some fluvial deposits. Basin development occurred during two stages separated by an inversion event, with the Kalgoorlie Terrane recording change from a fluvial to a deep-marine basin and the Kurnalpi Terrane change from distal to proximal deep-marine facies tracts. Sparse palaeocurrents establish that uplift to the north controlled sediment dispersal. Lithofacies stacking is aggradational, whereas abrupt upwards-change in facies tracts is back-stepping within depositional sequences, and between depositional-sequence sets, but forward-stepping between depositional sequences. The stratigraphic architecture is atypical of synorogenic basins but consistent with a strike-slip regime characterised by pulsed uplift-subsidence, steady-state basin lengthening and subsidence, punctuating catastrophic subsidence and lengthening, and tectonic anchoring.The basins are interpreted to have been similar to graben and half-graben of the Western Anatolian extensional province of Turkey, with linear zones of subsidence developing adjacent to strike-slip, oblique-slip or normal dip-slip faults. Controls on stratigraphic patterns are considered to have been regional rather than at the scale of each basin. The envisaged tectonic setting is similar to projected collision between the Philippine Archipelago west of the Philippine Fault and continental crust of the South China Sea, but the orogenic architecture is similar to that of accreted superterranes in the Canadian Cordillera. Interpreted north- or northwest-convergence between the Burtville Terrane to the east and the ancestral Yilgarn continent to the northwest produced a south-propagating orogen, with the Kalgoorlie, Gindalbie, and Kurnalpi Terranes trapped between in a tectonic-escape corridor. Tectonic escape to the south between bounding strike-slip faults produced back-stepping of facies tracts that simulated basin lengthening, whereas forward-stepping of facies tracts was the response to south-propagating uplift.