Ongoing capture of the
Baja California microplate

John Fletcher, Ph.D.
Departamento de Geología, CICES

Wednesday, July 10, 2002
3:00 p.m.–Pacific Forum

The Baja California microplate is separated from both the Pacific and North American plates by extensive fault systems that have reactivated preexisting crustal weaknesses. Fault systems in the Gulf of California originally exploited thermally and mechanically weakened lithosphere along the axis of the early-middle Miocene volcanic arc. Whereas, in the Pacific borderland of Baja California, faults have reactivated a thick accretionary complex that likely extends beneath the microplate. The timing and kinematics of faulting in these two deformation provinces give important new insight into the mechanical evolution of the plate margin, establish new genetic relationships between core-complex-style rifting and seafloor spreading, and provide an explanation for why seafloor spreading ceased across more than 1000 kilometers of oceanic ridges to the west of Baja California only to be regenerated in the Gulf of California after approximately12 million years of continental rifting.