An important objective of Deep Sea Drilling Project
(DSDP) Leg 65 was to study crustal accretion at an ocean
ridge axis with an intermediate-spreading rate for comparison
with previously studied sections displaying slowand
fast-spreading rates. The southern Gulf of California
was selected for this purpose because the basement displays
high seismic velocities (comparable to those observed
for Cretaceous basement in the western North
Atlantic) and high ambient sedimentation rates, which
facilitated penetration of zero-age basement. Four sites
were drilled, forming an axial transect immediately south
of the Tamayo Fracture Zone (Figs. 1 and 2) and providing
a series of characteristic sections into the crust. This
chapter attempts to provide a brief synthesis of the results
from Leg 65, focusing particularly on the lithology,
geochemistry, and paleomagnetic properties of the
cored basement material. From these data, we present
an interpretation of the processes of magmatic evolution
and crustal accretion occurring at the Gulf of California
spreading axis
