Ocean Drilling Program, United States

Site 1158 was located in Zone A, and was one of six sites along a generally north-south line that were intended to locate possible occurrences of Indian-type mantle beneath western Zone A Hole 1158A produced 0.8 m (5.9% recovery) of aphyric to sparsely olivine plagioclase phyric basalt with a few glassy rinds. It was abandoned because of poor drilling conditions Hole 1158B yielded 1.6 m (10.7% recovery) of aphyric to sparsely olivine plagioclase phyric basalt. The basalt is slightly to moderately altered. It too was abandoned because of poor drilling conditions. Hole 1158C yielded 1.61 m (17.1%) of massive diabase (composed of plagioclase, clinopyroxene, and magnetite/ilmenite with a medium-grained subophitic texture) beneath overlying aphyric basalt rubble. Two lithologic units were identified. Unit 1 was similar to A and B and Unit 2 was a diabase. Low-temperature alteration products were present throughout this core. Ba and Zr systematics indicate that Site 1158 lavas were derived from Pacific-type mantle <2 mu after the Indian-type lavas of Site 1157 were erupted on the same flow line. 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)