Preliminary petrology of diabases from Sites 469 and 471, Deep Sea Drilling Project Leg 63.

Diabasic rocks were recovered at Sites 469 and 471 on IPOD/DSDP Leg 63. The diabasic rocks are composed mainly of plagioclase, clinopyroxene, and low-temperature alteration products. In addition to these phases, a considerable amount of primary biotite and lesser colorless amphibole are observed in some of the Site 471 diabases. Major and trace element data suggest that these rocks are tholeiitic; however, their highly altered nature obscures their petrologic affinity with the DSDP Leg 63 tholeiitic basalts and others from the nearby Pacific ocean floor. It is likely that the Site 469 and 471 diabasic rocks represent products of off-ridge intrusive activity.-Authors