Physical Properties of IBM Forearc Crust: Comparison with Oceanic Crust

Abstract:

Most of the well-preserved ophiolite complexes are believed to form in supra-subduction zone settings. One of the goals of IODP Expedition 352 is to test the supra-subduction zone ophiolite model by drilling forearc crust at the northern Izu-Bonin-Mariana (IBM) system. IBM forearc drilling is expected to sample sediment, lavas, and dikes. We will compare seismic velocities and other physical properties with lava and dike composition and stratigraphy at the Expedition 352 sites, particularly focusing on changes across the lava-dike transition. The IBM forearc results will be compared with observations of intermediate-spreading and fast-spreading rate oceanic crust drilled at Sites 504B and 1256D. Specific questions that will be addressed include: 1) At Site 504B the seismic layer 2/3 boundary is located near the top of the dike unit, while at Site 1256D it is located near the top of the gabbro unit. Is the lava-dike boundary at Expedition 352 associated with a seismic boundary, and if so, is it equivalent to the seismic layer 2/3 boundary? 2) At Sites 504B and 1256D there is a correlation between seismic velocities, porosities, and the presence of hydrothermal minerals. Is there a similar correlation at the Expedition 352 sites?