Sumatra

Sumatra is situated on the southern edge of Sundaland north of the Sunda Trench. The Sumatran Arc has a classic morphology of trench, accretionary prism, outer-arc ridge, forearc and volcanic chain with active andesitic volcanism, and there is a well-defined Benioff zone. Between north Sumatra and Java the subduction direction changes from oblique to almost orthogonal and India-Sundaland motion is partitioned into trench-normal subduction and dextral slip on the Sumatran Fault and related strands. A sliver plate is thus decoupled from the Sunda and Indian Plates and moves northwest although it is not entirely rigid but is subject to arc-parallel stretching.
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This part of the Sundaland margin has a very long subduction history which extends back to at least the late. Sumatra is underlain by continental crust dating from the Permo-Carboniferous to which were accreted a number of terranes during the Mesozoic and the island acquired a structural grain broadly parallel to its length. A collision between Sumatra-West Java and a narrow Woyla terrane terminated Mesozoic arc activity and Cenozoic rocks unconformably overlie Mesozoic rocks. Regional uplift was followed by extension and subsidence in the early Cenozoic although this is not well dated; the oldest parts of the sequence include volcanic rocks and sediments devoid of fossils. The origin of the Sumatra Basins is uncertain, partly because of the uncertainty in their age of initiation. Both strike-slip and extensional controls have been proposed. There was short-lived plutonism in the Early Eocene (60-50 Ma) but most Cenozoic activity dates from the early Miocene (20-5 Ma) when the present forearc-arc-backarc became established.

Recent Papers –

Max Webb et al., 2020. Isotopic mapping reveals the location of crustal fragments along a long-lived convergent plate boundary. Lithos.

https://doi.org/10.1016/j.lithos.2020.105687

Max Webb et al., 2020. The history of Cenozoic magmatism and collision in NW New Guinea – New insights into the tectonic evolution of the northernmost margin of the Australian Plate. Gondwana Research.

https://doi.org/10.1016/j.gr.2019.12.010

Amy Gough et al., 2020. Mid-Cenozoic fluvio-deltaic to marine environments of the Salin Sub-basin, Central Myanmar. Journal of Asian Earth Sciences.

https://doi.org/10.1016/j.jseaes.2019.104143

Recent News –

Amy Gough and Max Webb attended the Restech 2.0 Virtual Reservoir Conference. Amy Gough presented new SEARG research on the pitfalls of light mineral studies for sedimentary provenance in tropical climates.

Amy Gough was awarded an honorary research fellowship of the British Geological Survey and continues to foster collaborative relationships between SEARG and the BGS.