Plate tectonics and the development of sedimentary basins of the dextral regime in western Southeast Asia

Abstract

The western part of Southeast Asia is comprised of three tectonic plates: the Southeast Asia Plate, the Burma Plate, and the Australia-India Plate. The present regime of oblique subduction and partial coupling of the combined Australia-India Plate to the Southeast Asian part of the Eurasia Plate was initiated in the Middle Eocene. Resulting dextral shear interacting with the inertia of the largely continental plate were the driving forces of basin genesis and development, setting in train a sequence of temporally and spatially variable tectonic events, diminishing in intensity away from the active plate boundary. The effects can be identified in the east from the Malay Basin to Central Thailand. A Late Eocene to Oligocene rifting phase formed rift troughs in central Sumatra, later spreading north to the Mergui Basin and south to the Sunda Basin. The Sunda Volcanic Arc was initiated. As subduction proceeded, deformation spread out from the vicinity of the plate boundary. In the Oligocene, dextral shear, substantially along preexisting faults and consequential extensional faulting initiated the Thailand basins and the Malay Basin. Subsidence and extension continued until late Middle Miocene time, possibly with some thermal relaxation. In the Late Oligocene to Early Miocene, the back arc basins close to the plate boundary began to subside, extending out from the initial rift troughs during a quiescent interval transition between the rifting and later wrenching phases. Subsidence may have been the result of the withdrawal of heat from the asthenosphere beneath the basins by the cold subducted slab. As the Sunda arc-forearc developed by accretion and magmatism, partial coupling in the plate boundary region was enhanced and transpressional deformation commenced in the Sumatra basins in the Middle Miocene. This Sea defining the northern part of the Burma Plate. South of the Andaman Sea, deformation persisted in a broad zone along the margin of the Southeast Asia Plate. Dextral wrenching in the late Middle Miocene phase affected much of the eastern region, extending south into the Natuna Basin. Deformation diminished markedly at the end of the Middle Miocene with the inception of the Burma Plate. Transpressional tectonics continued through Late Miocene and Pliocene time in Sumatra, in a broad zone as an ill defined southern extension of the Burma Plate. The continuing movement resulted in the uplift of the Barisan Mountains and the deformation of the onshore Sumatra basins. The Sumatra forearc was transferred to the Burma Plate with the establishment of the dextral Sumatra Fault probably in the Pliocene.