Izu-Mariana Margin

Abstract

Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation, the participating agencies, Joint Oceanographic Institutions, Inc., Texas A&M University, or Texas A&M Research Foundation. This Scientific Prospectus is based on precruise JOIDES panel discussions and scientific input from the designated Co-chief Scientists on behalf of the drilling proponents. The operational plans within reflect JOIDES Planning Committee and thematic panel priorities. During the course of the cruise, actual site operations may indicate to the Co-chief Scientists and the Operations Manager that it would be scientifically or operationally advantageous to amend the plan detailed in this prospectus. It should be understood that any proposed changes to the plan presented here are contingent upon approval of the Director of the Ocean Drilling Program in consultation with the Science and Operations Committees (successors to the Planning Committee) and the Pollution Prevention and Safety Panel. One outcome of Leg 185 will be the best existing mass balance of input and output fluxes for several key tracers (H 2 O, CO 2 , U, and Pb) cycled through the subduction factory. These data will permit a better understanding of the recycling of oceanic crust in the Earth's mantle, the formation of continental crust in arc systems and the role of recycled oceanic crust in the generation of mantle plume magmas. With Hole 801C, which penetrates the world's oldest in situ oceanic crust (~165 Ma), the science party will also provide the first reference site for the structure and composition of old, fast-spreading oceanic crust to compare with other crustal end-members. Based on the seismic structure of the East Pacific Rise crust formed at comparable spreading rates (160 mm/yr full rate), the upper 450 m at Hole 801C may include the entire extrusive section, or layer 2A, of the oceanic crust. Thus, it is possible that Leg 185 will provide the second example of in situ oceanic crust into the sheeted dike complex. Leg 185 Scientific Prospectus Page 4Leg 185 has been targeted to conduct contamination testing and development of a standard sampling procedure for deep biosphere research. The objective of the contamination test is to determine the amount of mixing created by the coring process by introducing a tracer (latex beads)at the mouth of the core barrel as the core is cut.