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Continental Transform Zones |
Centro di Geodinamica, Università della Basilicata, 85100, Potenza, Italy
The complex structural setting of the western margin of North America is interpreted to result from oblique convergence of the North American and Pacific plates, accommodated by both right-lateral slip along the San Andreas fault and shortening east and west of it. Strike-slip movements along the San Andreas fault led to the detachment of a continental fragment (the Salinian Block) from the North American margin during early Miocene, and its translation northwestwards for over 300 km. Structural analysis in the Northern Salinian Block, west of the San Andreas fault, reveals a NE-SW-directed shortening accommodated by NW-SE-trending folds and thrusts with a dip-slip kinematic character. The stratigraphic record of progressively younger unconformities affected by both folds and thrusts, as well as the overprinting relationships among these contractional structures, enables us to clarify the tectonic evolution of the region since Paleocene time. The Paleocene to Recent history of the Salinian Block was dominated by strike-slip along the San Andreas fault, and by shortening perpendicular to it. The partitioning between strike-slip and dip-slip movements appears to be controlled by a pre-existing tectonic feature. The results from structural analysis along the Salinian Block are integrated into a deformation model for the western margin of North America, providing additional constraints on the timing of deformation and helping to clarify the role of strain-partitioning processes in the obliquely convergent California margin.
