Radiometric ages of basaltic basement recovered at Sites 800, 801, and 802, Leg 129, western Pacific Ocean

Abstract

ODP Leg 129 achieved one of its primary goals by recovering Jurassic-age ocean crust at Site 801 in the Pigafetta Basin, western Pacific Ocean. At Sites 800 and 802, although also located on presumed Jurassic-age crust, drilling terminated in the ubiquitous Cretaceous-age volcanic rocks that seem to blanket the Early Cretaceous and Jurassic basement of the western Pacific Ocean. Site 801 penetrated 131 m of basaltic flows divided into an upper sequence of alkalic basalts, an altered hydrothermal deposit, and a lower tholeiitic sequence. For the lower tholeiitic basalts, whole rock incremental- and laser-heating experiments revealed an age of 166.8 ± 4.5 Ma. The age and composition of the tholeiites offers important proof that the "Quiet Zone' crust of the western Pacific is indeed Jurassic mid-ocean ridge basalt (MORB), and not a product of mid-Cretaceous, intra-plate volcanic events. -from Author