Reevaluation of California Coastal Continental Borderland Evolution: Recent Evidence from Stratigraphic, Geophysical, and Paleomagnetic Studies
E. L. Ambos, S. P. Lund, F. Theyer, D. Bottjer, T. L. Henyey
Tectonostratigraphic terrane analyses applied during the past decade to California continental borderland evolution distinguished eight or nine terranes that may have docked in the borderland from Cretaceous to mid-Tertiary time. These terranes may in turn be grouped into two composite terranes--the Peninsular Ranges terrane (PRT) and the more northerly Santa Lucia-Orocopia Allochthon (SLOA)--that sutured together during the late Oligocene to mid-Miocene in the southwestern Transverse Ranges. In parallel, the last decade has seen continued refinements in stratigraphy, sea level history, and the accumulation of a large data base of paleomagnetic measurements in southern California. These newly refined data necessitate the reevaluation of the timing sequence of terrane amal amation in the borderland, and a new scenario for the docking of the PRT against the SLOA can be constructed. Of equal importance in the tectonic reconstruction of the borderland is the consideration of paleoclimatological signals, which may mask or conflict with "true" terrane interactions. For example, a growing body of evidence indicates that prominent reflectors noted in borderland seismic records may correlate with global Neogene paleo-oceanographic events, rather than tectonic events. In addition, recent geophysical investigations of terrane suture zones and the crustal structure beneath terranes in other areas of the western United States provide intriguing information on the nature of terrane boundaries. In this context, the PRT-SLOA suture appears as the most fundamental terrane boundary, marked by a zone of high-density, high-velocity material, whereas other terrane boundaries, particularly within the PRT, appear to be of secondary importance.
AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.