Origin and tectonic development of Malay-Penyu-West Natuna basins

Abstract

A Late Cretaceous hot spot arches up continental crust of the northern Sunda Shelf into the Malay Dome (new name). Its crest breaks into three rift arms that are now represented by the Malay, Penyu and West Natuna basins. Its triple junction is still one of the highest heat-flow areas of the region. By Middle Eocene time hot spot activity had ended allowing the basins to become aulacogens into which perhaps up to 12 km thick upper Oligocene and younger sediments accumulated. At the same time, hard collision of the Indian Subplate with Asia differentially pushes out elongated crustal slabs of Southeast Asia towards southeast along major NW-striking wrench faults, one of which is located in the basement rocks along the axis of the Malay Basin. Left-lateral motion along this Axial Malay (new name) fault zone develops east-west half grabens and grabens as special depocentres of the basin. By early Middle Miocene, the westward drive of the Pacific Plate is no longer buffered by spreading of the South China Sea Basin and causes reversals in slip sense along the wrench faults and other structural inversions. The Axial Malay faults now move right-laterally deforming the sediments in the half grabens and grabens into east-west anticlines and south-verging thrust faults. Other factors that have effected the regional stress field changes are the close approach of the northward moving Indian Ocean-Australia Plate, and by early Late Miocene also the opening of the Andaman Basin.