Revised plate tectonic history of the west Australian margin reveals how the Gascoyne Terrane docked at West Burma

Abstract

Southeast Asia contains various continental fragments that sequentially rifted from East Gondwana. A number of these fragments were sourced from the northern margin of East Gondwana. East Gondwana's fragmentation was initialised with Late Jurassic rifting along the northwest Australian margin, forming the Argo Abyssal Plain, and followed by Early Cretaceous N-S oriented rifting along the entire western Australian margin, forming the Gascoyne, Cuvier and Perth Abyssal Plains. In a comprehensive study to address the issue of margin formation and terrane drift and docking, we revised the tectonic formation of the entire margin using an integrated analysis of marine magnetic and gravity anomaly data from all abyssal plains involved. Our model highlights the necessity for a new continental fragment, the Gascoyne Terrane, due to the presence of tectonic features, such as margin age offsets, spreading rates, ridge jumps and isochron orientations, that are distinctly different north and south of the Wallaby Zenith Fracture Zone (WZFZ). Our model suggests that the northern extent of Greater India was limited by the WZFZ. The relative motion between Greater India and Australia formed the Perth Abyssal Plain, while motion of the Gascoyne block, located north of the WZFZ, formed the Cuvier and Gascoyne Abyssal Plains. Following rifting from the northwest margin north of the Exmouth Plateau, Argoland accreted to Burma at ~75 Ma. Our model suggests that in contrast the Gascoyne Terrane was accreted to West Burma at ~55 Ma, following about 20 million years of Tethys seafloor subduction after Argoland's accretion. Our model also suggests that the eastern tip of Greater India collided with West Burma at around 35 Ma. This is consistent with the onset of extrusion of the North Indochina Block around 34 Ma, expressed by leftlateral strike-slip along the Ailao Shan - Red River shear zone between 34 and 17 Ma. Burma is rich in gems, lead, zinc, iron, tin, chromium, nickel and tungsten deposits, and has oil-bearing fields in its forearc basin. Our model has implications for the formation of the West Burmese margin, as it would also be comprised of a continental terrane once conjugate to the Bernier Platform and Exmouth Plateau, both proven hydrocarbon-rich resources. Advances in modelling the accretion history of Burma will help to distinguish possible continental fragments, which may reveal new resources.