Fluid flow and diagenesis in the incoming oceanic plate lithostatigraphy to the Sumatra subduction zone: a geochemical approach

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On 26 December 2004, the Sumatra-Andaman earthquake with a moment magnitude of Mw=9.2 ruptured approx. 1300 km of the plate interface with coseismic slip propagating seaward to the trench causing the devastating tsunami. The event is unusual because the plate boundary thrust beneath the outermost accretionary prism is usually assumed to be aseismic. A high degree of lithification in the incoming section has been proposed to explain the seaward shift of seismogenic slip and the unusual geometry of the Sumatra accretionary prism. However, validation of this hypothesis is still outstanding because the sedimentary input to the Sumatra subduction zone has not been specifically sampled by scientific ocean drilling so far.The main focus of this research proposal will be the identification and spatio-temporal characterization of important diagenetic, alteration and fluid flow processes in the incoming sediment and oceanic crust to the Sumatra subduction zone. The research will be implemented by geochemical analysis of both pore fluids and sediment/basement samples that will be sampled offshore NW Sumatra during Expedition 362 of the International Ocean Discovery Program in 2016. In detail the work program will encompass: (1) Identification of water-rock interaction processes and their source depths via lithium and boron isotope analysis in combination with fluid and whole rock geochemistry and X-ray diffraction analysis, and (2) integration of the geochemical data with results from flow-through experiments and reaction transport models to understand the hydrogeology of the incoming oceanic plate lithostratigraphy.