Tectonics and geological history of the passive continental margin at the tip of Baja California ( DSDP, Leg 64).

Abstract

The three-site Leg 64 Deep Sea Drilling transect at the tip of the Peninsula of Baja California straddled the transition from continental to oceanic crust. The outer site, 474, penetrated mainly mud turbidites and bottomed in 'middle' Pliocene oceanic crust about 3Ma old. Two sites on the lower continental slope penetrated hemipelagic muddy sediments, a thin section of low-oxygen, phosphoritic, and glauconitic sediments, and a metamorphic cobble conglomerate; one of the sites, 476, bottomed in deeply weathered granite. The oldest marine sediments at this site are early Pliocene, about 4.5Ma old. Depth indicators in these holes suggest that all sites were in almost 1000m of water by the time oceanic crust was first generated and sea-floor spreading began. Block faulting, subsidence, and deposition of marine sediments on continental crust had proceded the start of sea-floor spreading. -from Authors