T32C-03
Physical Properties and Seismic Structure of Izu-Bonin-Mariana Fore Arc crust: Results From IODP Expedition 352 and Comparison with Oceanic Crust
Wednesday, 16 December 2015: 10:50
304 (Moscone South)
Gail Lynn Christeson1, Sally Morgan2, Shuichi Kodaira3, Mikiya Yamashita3 and IODP Expedition 352 Scientists, (1)UTIG, Austin, TX, United States, (2)University of Leicester, Department of Geology, Leicester, United Kingdom, (3)JAMSTEC Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan
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 was to test the supra-subduction zone ophiolite model by drilling forearc crust at the northern Izu-Bonin-Mariana (IBM) system. IBM forearc drilling successfully cored 1.22 km of volcanic lavas and underlying dikes at four sites. A surprising observation is that basement compressional velocities measured from downhole logging average ~3.0 km/s, compared to values of 5 km/s at similar basement depths at oceanic crust sites 504B and 1256D. Typically there is an inverse relationship in extrusive lavas between velocity and porosity, but downhole logging shows similar porosities for the IBM and oceanic crust sites, despite the large difference in measured compressional velocities. These observations can be explained by a difference in crack morphologies between IBM forearc and oceanic crust, with a smaller fractional area of asperity contact across cracks at EXP 352 sites than at sites 504B and 1256D. Seismic profiles at the IBM forearc image many faults, which may be related to the crack population.
