Chemical cycling in the Japan subduction zones: Solid-fluid budgets using isotopic proxies

• Applicant: Dr. Annette Deyhle
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2002 to 2005
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5354610

Subduction zones are the places on Earth where recycling of sediments and crust into volcanic arcs and mantle melt takes place. Despite some of the processes in the so called "subduction factory" are principally understood, there is a great lack of quantitative estimates. The aim of the proposed project is to balance geochemical budgets across two typical subduction zones, which have become a major focus of marine geosciences: The Nankai and Japan Trench margins in the southwestern Pacific. In addition to ten deep sea drilling expeditions, the entire Integrated Ocean Drilling Program (IODP, starting at 2003) addresses the deep seismogenic subduction zone off Japan. Consequently, the research proposed can be envisaged as an important pilot study following a two-step approach. First, the element composition of major, minor and trace constituents as well as the isotopic fractionation of suitable proxies (B, Sr, Cl, O, H) from sediments and fluids will help to determine volatile flux and fluid-rock interaction. Second, the results and already existing chemical data will be tied together to model chemical behavior of selected proxies with increasing temperature, pressure, and time in the subduction zone. This chemical balance will quantitatively oppose the Nankai system with a large accreted wedge (and hence very little sediment entering the deep subduction zone) and the Japan Trench, where massive erosion supplied much material for deep recycling. The overall results are expected to better constrain elemental fluxes in the Japan subduction zone, but become globally significant when extrapolated to other margins.

• DFG Programme: Emmy Noether International Fellowships