Cenozoic deformation in Sumatra: oblique subduction and the development of the Sumatran Fault System

Abstract

Abstract Sumatra is situated at a long-lived active continental margin. At the present day, subduction beneath the margin is strongly oblique, leading to subduction of Indian Oceanic crust at the Sunda Trench and right-lateral strike-slip along the onshore Sumatran Fault System (SFS). A pre-Tertiary history of accretion against the margin was followed by Palaeogene basin formation throughout Sumatra. A strong mid-Miocene inversion event is recorded in the onshore part of the forearc basin in southern Sumatra. The mid-Miocene also marked the inception of seafloor spreading in the Andaman Sea and the probable inception of major strike-slip movement along the SFS, possibly following clockwise rotation of Sumatra towards it present NW-SE trend. The SFS exhibits a wide variety of geometries and deformational styles and is characterised by an extremely complex deformation history including polyphase reactivation of fault surfaces and contemporaneous strike-slip and orthogonal compression or extension. A new estimate of approximately 150 km offset of Mesozoic units across the SFS in central Sumatra is proposed. Several basins have formed along the SFS during the Quaternary. Some of these are not readily explained in terms of classic models of strike-slip basin formation and it is proposed that thermally induced uplift along the axis of the volcanic arc of the Barisan mountains was of primary importance in their formation.