Ocean Drilling Program, United States

This site was intended to check for Indian-type mantle between Sites 1158 and 1159. If it is of Indian type, it could test whether rift propogation reintroduced Pacific-type mantle beneath the region. Hole 1161A produced 4.4 m (15% recovery) of basaltic rubble with fragments of plagioclase-olivine phyric basalt breccia. Between the larger clasts is a finer-grained breccia with clasts of altered basalt and palagonitized glass in a clay-rich sediment matrix. This hole was abandoned due to drilling problems Hole 1161 B is composed of aphyric to highly plagioclase olivine phyric basalt and basaltic breccia. Both holes were moderately to highly altered by low-temperature reactions. Za/Br systematics of 1161A basaltic glass indicate Indian-type mantle source. The glass has a high Na (sub 2) O/TiO (sub 2) relative to other Leg 187 compositions and is therefore Indian type. This occurrence, separated by <1 Ma from the Pacific type mantle beneath site 1158, documents a second incursion of Indian-type mantle into Zone A (1157 is the first).(LEL)