ABSTRACT: Relationship of the Central Salinian Block, the Surobispo Terrane, and the Sierra Nevada in the Late Cretaceous Based on Paleomagnetic Evidence
WHIDDEN, KATHERINE J., STEVE P. LUND, and DAVID J. BOTTJER, University of Southern California, Los Angeles, CA, DUANE CHAMPION and DAVID G. HOWELL, U.S. Geological Survey, Menlo Park, CA
New paleomagnetic evidence from the central block of Salinia indicates that Salinia was within 6 degrees of its present position with respect to North America in the Late Cretaceous. These new results are from red beds intercalated within a fluvial conglomerate/sandstone sequence that lies conformably on granites of the central block of Salinia in the La Panza Range. The red bed samples showed two components of magnetization upon thermal demagnetization. First, a low-temperature (<300 degrees C) present-day overprint and second, a high-temperature (>400 degrees C) component. The high-temperature component has stable characteristic remanences of mixed polarity that pass a fold test. We interpret this component to be a hematite CRM.
Previous models for the tectonic evolution of coastal California have focused on the relative autochthoneity or allochthoneity of the entire region west of the San Andreas fault.
These results suggest a new model for the tectonic evolution of coastal California. Paleolatitude estimates from the Sierra Nevada batholith are consistent with as much as 5 degrees of northward motion, which ties in well with our results from the central Salinian block. Earlier paleomagnetic results indicating 2000+ km of northward transport of the Salinian and Sur-Obispo terranes actually may apply only to the terrane history of Sur-Obispo, a Franciscan-based terrane west of the Sur-Nacimiento fault zone. The northward motion of terranes along the western edge of California has been considered to be caused by oblique subduction along the margin throughout the Paleogene. This translation may have caused slight movement within the arc, and "tectonic smearing- of the outboard accretion ry prism units.