Ocean Drilling Program, United States

Site 1157 was located in Zone A. The purpose of this site was to test for occurrences of Indian-type mantle beneath Zone A. Hole 1157A was abandoned because of the drilling problems of poor drilling conditions and recovery. 2.9 meters of rubble were recovered. The rubble was made up of basalt and basalt-carbonate breccia; both aphyric and moderately plagioclase-olivine phyric basalts were present. All material from this hole has been assigned to one lithologic unit; basaltic rubble with intervals of basalt-carbonate breccia. The unit is composed of poorly sorted lithic clasts derived from aphyric basalt and moderately plagioclase-olivine phyric basalt. Alternation of clasts preceeded final brecciation with some (some halos terminate at a broken clast surfaces), other clasts are rimmed by low-alteration halos. Hole 1157B yielded 11.7 meters (29% recovery) of sparsely to moderately plagioclase-olivine phyric pillow basalt. The basalt had a moderate degree of low-temperature alteration. As in all the sites up until now, the rocks have lower MgO contents than the glasses. Ba and Zr contents suggest an Indian-type mantle source for lavas at Site 1157; this is the first Indian trace element signature observed in Zone A. Igneous petrology, alteration, microbiology, structural geology, site geophysics, sediments, and geochemistry studies were carried out. Data tables and figures are found at the end of the chapter.(LEL)