Ocean Drilling Program, United States

Site 1159 was located in Zone A, and was the youngest seafloor drilled during Leg 187 and southernmost site along the transect designed to locate possible occurrences of Indian-type mantle beneath western Zone A. Hole 1159A was the only hole drilled; it produced 7.96 m (28.7% recovery) of aphyric basalt with a few pieces of hyaloclastite breccia with interstitial sediment. The basalts were assigned to a single unit of moderately altered aphyric pillow lava with alteration halos along piece margin and veins The Ba and Zr contents of the glasses indicate a Pacific-type mantle reservoir beneath this site. This site was the fourth Pacific site of five sites drilled in western Zone A, reinforcing the conclusion that the Indian/Pacific mantle boundary is closely associated with the eastern margin of the depth anomaly. Data tables and figures are found at the end of the chapter.(LEL)