Abstract: Neogene Transfer of Central California to the Pacific Plate: Evidence from Santa Maria Basin, California

P A McCrory, D S Wilson, J C Ingle Jr., R G Stanley

The central California margin records a complex response to changing plate motions during the Cenozoic. The record of Cenozoic tectonism preserved in Neogene basin strata, integrated with plate reconstructions, provides insights into the evolution of the margin during its transition from a convergent to a transform plate boundary and its transfer from the North America to the Pacific plate. In particular, the continuation of subduction of the Monterey microplate in the Miocene has significant implications for evolution of the San Andreas transform boundary.

Subduction of the Monterey microplate continued until ca. 19 Ma, when the Pacific-Monterey ridge, adjacent to Santa Maria basin, stopped spreading and the relict Monterey microplate was transferred to the Pacific plate. Onset of late early Miocene subsidence and volcanism along the central California margin likely results from the subsequent formation of a transtensional plate boundary. The initial rapid phase of subsidence in Santa Maria basin, from 18-16 Ma, is attributed to local extension of the continental crust associated with onset of western Transverse Range rotation triggered by Monterey microplate capture. A subsequent slower phase, from 16-7 Ma, is attributed to thermal subsidence associated with cooling of underplated oceanic lithosphere which had moved northwestward with he Pacific plate to a location beneath the Santa Maria basin area.

Onset of transpression across the Pacific-North America transform boundary in the latest Miocene is approximately coeval with a phase of dip-slip faulting and bathymetric reversal in Santa Maria basin. The pattern of uplift and subsidence documented by backstrip analysis likely reflects crustal shortening, in agreement with a transpressive regime. Thus, existing geologic constraints are consistent with a plate kinematic mechanism for tectonism along the central California margin.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California