Abstract

A minimum of 75 km of right-lateral fault displacement occurred within the Franciscan assemblage of northern California, most likely in late Tertiary time. This displacement is inferred from the present position of two geologically unrelated units, the rocks near Black Lassie, California, and the Redwood Creek schist. The Black Lassie rocks show at least 75 km of northward displacement from their source terrane within the Coast Range ophiolite. Although no conclusive evidence of northward transport for the Redwood Creek schist is available, the geologic setting of the schist and the nature of the faults that bound it strongly suggest that the Redwood Creek schist has also been laterally transported many tens of kilometres northward. We propose that both these units moved northward by means of one or a few major north-northwest–trending right-lateral faults that were active in the forearc basin off the California coast during right-oblique subduction of the Farallon plate under the North American plate in late Tertiary time.

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