Sundaland basins

The continental core of Sundaland, comprising Sumatra, Java, Borneo, the Thai-Malay Peninsula and Indochina, was assembled during the Triassic Indosinian orogeny, and formed an exposed landmass during Pleistocene lowstands. Because the region includes extensive shallow seas, and is not significantly elevated, it is often assumed to have been stable for a long period. This stability is a myth. The region is today surrounded by subduction and collision zones, and merges with the India-Asia collision zone. Cenozoic deformation of Sundaland is recorded in the numerous deep sedimentary basins alongside elevated highlands. Some sediment may have been supplied from Asia following Indian collision but most was locally derived. Modern and Late Cenozoic sediment yields are exceptionally high despite a relatively small land area. India-Asia collision, Australia-SE Asia collision, backarc extension, subduction rollback, strike-slip faulting, mantle plume activity, and differential crust-lithosphere stretching have been proposed as possible basin-forming mechanisms. in scale, crustal character, heat flow and mantle character the region resembles the Basin and Range province or the East African Rift, but is quite unlike them in tectonic setting. Conventional basin modeling fails to predict heat flow, elevation, basin depths and subsidence history of Sundaland and overestimates stretching factors. These can be explained by interaction of a hot upper mantle, a weak lower crust, and lower crustal flow in response to changing forces at the plate edges. Deformation produced by this dynamic model explains the maintenance of relief and hence sediment supply over long time periods.