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Compression of Salinian Block in Monterey Bay Region

H. Gary Greene, David S. McCulloch, Joseph C. Clark

The Salinian block marks the broad boundary between the North American and Pacific plates in the Monterey Bay region. Here, this structural block is known as the Salinian composite terrane, a tectonostratigraphic terrane of Cretaceous granitic rocks that is cleanly bounded by the San Andreas fault to the east and irregularly bounded by the Sur, Nacimiento, Palo Colorado, and Ascension faults to the west. Present-day oblique plate motion results in northward extension and fragmentation of the block. Along the shelf margin north of Monterey Bay, the western margin of the block is being sheared and pulled apart by northward translation of the Pacific plate.

Recent fieldwork on the Salinian block in the Monterey Bay region indicates that transpression is responsible for distortion and elongation of the block. Side-scan sonographs and Uniboom seismic-reflection profiles collected across the Monterey Bay fault zone show secondary thrust faults and folds associated with primary northwest-southeast-oriented transcurrent faults. Ongoing detailed mapping of the Navy-Tularcitos fault zone shows the same type of relationship to be present onshore.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.