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Cenozoic geodynamic evolution of the Andaman–Sumatra subduction margin: Current understanding



The Andaman–Sumatra margin displays a unique set-up of extensional subduction–accretion complexes, which are the Java Trench, a tectonic (outer arc) prism, a sliver plate, a forearc, oceanic rises, inner-arc volcanoes, and an extensional back-arc with active spreading. Existing knowledge is reviewed in this paper, and some new data on the surface and subsurface signatures for operative geotectonics of this margin is analyzed. Subduction-related deformation along the trench has been operating either continuously or intermittently since the Cretaceous. The oblique subduction has initiated strike–slip motion in the northern Sumatra–Andaman sector, and has formed a sliver plate between the subduction zone and a complex, right-lateral fault system. The sliver fault, initiated in the Eocene, extended through the outer-arc ridge offshore from Sumatra, and continued through the Andaman Sea connecting the Sagaing Fault in the north. Dominance of regional plate dynamics over simple subduction-related accretionary processes led to the development and evolution of sedimentary basins of widely varied tectonic character along this margin. A number of north–south-trending dismembered ophiolite slices of Cretaceous age, occurring at different structural levels with Eocene trench-slope sediments, were uplifted and emplaced by a series of east-dipping thrusts to shape the outer-arc prism. North–south and east–west strike–slip faults controlled the subsidence, resulting in the development of a forearc basins and record Oligocene to Miocene–Pliocene sedimentation within mixed siliciclastic–carbonate systems. The opening of the Andaman Sea back-arc occurred in two phases: an early (∼11 Ma) stretching and rifting, followed by spreading since 4–5 Ma. The history of inner-arc volcanic activity in the Andaman region extends to the early Miocene, and since the Miocene arc volcanism has been associated with an evolution from felsic to basaltic composition.