Ocean Drilling Program, United States

Leg 190 is the first of a two-leg program of drilling along two transects in the Nankai Trough, the type example of a convergent margin accreting a thick section of clastic sediments. The proposed sites will define the interrelationship of the dynamics of deformation and fluid flow processes in an accretionary prism characterized by thick terrigenous sediments. In situ measurements, including logging while drilling, will provide critical information on stress, pore pressures, and permeability. Sealing holes with advanced circulation obviation retrofit kits (ACORKs) will establish the framework for long-term observation of fluid flow parameters and fluid geochemistry. Our integrated structural, geochemical, and physical properties program will fully characterize the factors controlling development of this accretionary prism. Leg 190 will focus on core recovery from sites in undeformed to highly deformed zones along the transects to investigate variability in deformational and hydrologic character. A second leg in 2001, Leg 196, will involve logging the sites drilled on Legs 131 and 190 to obtain a first-order picture of how physical properties change during accretion, as well as emplacing ACORKs for long-term monitoring of fluid flow processes.