THE ROLE OF SHEAR ZONES AND LOWER CRUSTAL FLOW IN THE EVOLUTION OF THE V- SHAPED SEDIMENTARY BASINS

West and northwest-trending transcurrent faults divide Australia into blocks and belts. The Canning-New England Block that encompasses the Canning Basin at its northwestern end was more mobile than the adjacent blocks. Sinistral and dextral faults bound the block from the north and south respectably. Intermittent and major activity of these faults could trigger along strike decompression zones in the lower crust. The V- shaped sedimentary basins flanking the Canning-New England Block were created by multi-stage ductile movement of lower crustal material from the adjacent blocks towards the decompression zones and their offshore extension. The lower crustal flow was contemporaneous with wrenching in the overlying brittle cover, with sinistral and dextral strike-slip faults, that are orthogonal in trend to the major transcurrent faults. Along the basin lateral channel flow of lower crustal material and associated thermal perturbation is likely to account for subsidence and deformation along and across the V-shaped sedimentary basins. These transcurrent faults extend eastward to the Pacific subduction zone. The Cook and Vening-Meinesz Fracture Zones are likely to represent the most eastern extension of the proposed faults that defined the Canning-New England Block. They are displaced northeast because of anti-clock wise rotation of the Tasman Sea. The proposed lateral lower crust flow is self-induced mechanism and stress related and facilitated by low viscosity of mafic and ultramafic rocks that is inconsistent with hotspot and classical plume models. Similar tectonic setting is proposed for the Basin and Range Province. The seismicity in Australia and western USA are consistent with the proposed model.

Keywords:

V-shaped sedimentary basins , Transcurrent faults , Decompression zones , Lower crust , Tectonic