Alternative tectonic model for Late Jurassic through Early Cretaceous evolution of the Great Valley Group, California
Published:January 01, 2007
James E. Wright, Sandra J. Wyld, 2007. "Alternative tectonic model for Late Jurassic through Early Cretaceous evolution of the Great Valley Group, California", Convergent Margin Terranes and Associated Regions: A Tribute to W.G. Ernst, M. Cloos, W.D. Carlson, M.C. Gilbert, J.G. Liou, S.S. Sorensen
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The Franciscan Complex, Great Valley Group, and Sierra Nevada batholith have long been considered to represent a Cretaceous convergent margin assemblage. This subduction complex, forearc basin, and magmatic arc triad has also been considered to have formed essentially in place with little or no Cretaceous-age translation between any of the three parts. Below we explore the possibility that the Great Valley Group accumulated in a basin that was translated parallel to the convergent margin as a forearc sliver during the Late Jurassic–Early Cretaceous. There are three different scales of evidence that lead to this hypothesis. The first comes from the processes operating at modern convergent plate boundaries. The second line of evidence is based on analysis of the geologic relations where the Coast Ranges meet the Klamath Mountains province in northern California. Thirdly, we explore published and some new detrital zircon age data in the context of a translational model for the Great Valley forearc basin. We conclude that the Great Valley forearc basin is bounded on its eastern and northern sides by a strike-slip fault that accommodated several hundreds of kilometers of dextral offset in the Late Jurassic–Early Cretaceous. This boundary is now a highly modified fault separating the Klamath Mountains province and the Coast Ranges, across which are juxtaposed two fundamentally different parts of the Great Valley Group. The boundary continues to the south between the Sierra Nevada and the Coast Ranges, where it is buried beneath younger sediments of the Sacramento Valley and/or perhaps includes structures in the Sierran foothills such as the Melones fault. Detrital zircon data suggest to us that the most likely original location of the Coast Ranges Great Valley Group, prior to strike-slip offset, was offshore of the continental arc in the southwest Cordillera (southeast California to northwest Mexico). In addition, we discuss evidence that the boundary between the Franciscan subduction complex and Great Valley forearc basin experienced significant dextral displacement. Finally, we suggest that these plate-boundary-parallel faults are part of an even larger system of Early Cretaceous dextral strike-slip faults in the U.S. Cordillera, including the Mojave–Snow Lake fault, western Nevada shear zone, and Idaho shear zone.