Time scales for vertically moving axial magma chambers at fast-spreading ocean ridges and involved magmatic reactions: Insights from IODP Site 1256

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Models on the geodynamics of oceanic spreading centers imply that the axial magma chambers (AMC) under fast-spreading ridges are transient phenomena, moving up and down in distinct time scales which are only poorly quantified up to now. Thanks to IODP multi-cruise mission "Superfast Spreading Crust" (Site 1256, equatorial East Pacific Rise), a direct estimation of these time scales seems now possible. Expedition 312 drilled successfully a fossil conductive boundary layer (CBL): a horizon of metamorphosed, "granoblastic" dikes sandwiched between gabbros and sheeted dikes, providing the potential to obtain fundamental temporal information of the movements of the AMC/Dike transition. By applying modern tools of diffusion modeling to those phases within the "granoblastic" dike horizon, which were metamorphosed by the thermal imprint of the AMC in a high position, we aim to constrain the time scales of vertical movements of AMC's. During upward moving of an AMC into previously hydrothermalized dikes, vast reactions are expected causing assimilation and stoping. It is our attempt to simulate these processes experimentally, in order to understand/quantify the mechanism of the corresponding magmatic reactions for evaluation a general model, how contamination of MORB under fast-spreading ridges proceeds.