Myanmar and Asia united, Australia left behind long ago

Abstract

It is well known that western Myanmar is underlain by a continental fragment, the West Burma Block, but there are arguments about its origin and the time of its arrival in SE Asia. This study presents the first petrological, XRD diffraction, heavy mineral and detrital zircon U-Pb age data from turbidite sandstones in the Chin Hills that were deposited on West Burma crust in the Triassic. These sandstones contain detritus derived from areas surrounding West Burma and thus help resolve arguments about its location in the Palaeozoic and Mesozoic. West Burma, Sibumasu and Western Australia have similar populations of Archean zircons derived from Western Australian cratons. Until the Devonian all formed part of the Gondwana supercontinent. The abundance of Archean zircons decreases from Western Australia to West Burma and then to Sibumasu. This is consistent with their relative positions in the Gondwana margin, with Sibumasu furthest outboard from Western Australia. Differences in zircon populations indicate that Indochina was not close to West Burma or Sibumasu in Gondwana. West Burma contains abundant Permian and Triassic zircons. These are unknown in Western Australia and different from those of the Carnarvon Basin; they were probably derived from SE Asian tin belt granitoids. Cr spinel is present in most West Burma sandstones; it is common in SE Asia but rare in Western Australia. These new data show that West Burma was part of SE Asia before the Mesozoic and support suggestions that the Argo block that rifted in the Jurassic is not West Burma.