Bathymetry and oceanic crustal ages in the vicinity of the mouth of the Gulf of California, illustrated using Deep Sea Drilling Project Leg 63 underway geophysical profiles.

Abstract

We used recently acquired and rigorously navigated underway geophysical data from the region of the mouth of the Gulf of California to prepare detailed bathymetric and crustal age maps along a swath approximately 200km wide paralleling DSDP Leg 63 track lines between Sites 471, 472, and 473. The basement ages of the drilling sites, estimated from magnetic anomalies fit to time scale NLC-80, are 15.5Ma and 6.5Ma, respectively. These estimates are in agreement with biostratigraphically determined basement ages and support the proposal that an aborted ridge of about 13.7Ma of age has left a small fragment of the Farallon plate beneath the Magdalena Fan at 23.5oN, 112.5oW. In addition, we identify four large faults in the region, each of which is about 200km long, and several minor faults. In particular, the region SW of Cabo San Lazaro and W of Cabo San Lucas is complexly faulted. Our results contradict the recently proposed existence of a 3.5Ma old aborted spreading center W of the Tres Marias Islands. Alternatively, subduction of the Pacific plate beneath the SE tip of Baja California and concomitant strike-slip faulting W of the peninsula may be responsible for the uncentered location of the Rivera Ridge in the mouth of the Gulf of California.-Authors