Abstract: Miocene Extension and Rotation of South-Central California

C. C. Sorlien, C. Nicholson, B. P. Luyendyk, S. Cisowski, K. J. Bird, M. E. Tennyson

Neogene clockwise rotation of western Transverse Ranges (WTR) crust resulted in space problems along both its leading and trailing edges. Previous models linked rotation to transform motion, and include a nonrotated onshore and offshore Santa Maria Basin (SMB). We now know that transform boundary development was delayed by continued subduction of microplates along the south-central California margin until 19 Ma. As the subducted slab of the Monterey plate was captured by the Pacific plate after spreading stopped, the right-extensional basal shear rifted and rotated the upper-plate WTR away from the Peninsular Ranges. Existing paleomagnetic data indicate that blocks to the north and east of SMB are rotated ~45° and ~80°, respectively, while our preliminary results from SMB ar consistent with large rotation. Important shortening in onshore and offshore SMB is post-Miocene, and may be associated with continuing post-Miocene rotation of the WTR. In our 19 Ma reconstruction, the onshore and offshore SMB and the WTR are back-rotated 75-100+°. The model predicts that displacements in the wake of the WTR include 250 km of northwest-southeast dextral slip, 80 km of northeast-southwest extension, and 120+ km of northwest-southeast extension. Offshore of Pt. Arguello, dextral motion is limited to a few tens of kilometers, with extension also in all directions. As the trailing edge of the WTR became more parallel to the relative motion of the slab, the basal shear is expected to have induced slower rotation and increased sinistral shear.

AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994