STAKES, DEBRA S., and KAREN SALAMY, MBARI, Moss Landing, CA; RONALD W. KISTLER and DUANE E. CHAMPION, USGS, Menlo Park, CA; CATHERINE A. RIGSBY, ECU, Greenville, NC

Abstract: Isotopic and Lithologic Constraints on the Tectonic History of Monterey Canyon

A model for the tectonic history of Monterey Canyon has been developed based on detailed ROV sampling of the Monterey, Soquel and Carmel Canyons, combined with recent EM300 sidescan and bathymetric data. Within Soquel Canyon, Cretaceous biotite granites were intruded by a basaltic andesite about 23 my ago (age based on Ar/Ar of basaltic plagioclase), forming a peperite in overlying coarsegrained sandstone. In addition, this calcite-cemented sandstone varies lithologically from the adjacent Monterey Formation. Rather there are strong similarities to the peperite-sandstone-dolomite vein of the Vaqueros Formation at Pescadero Point. These lithologies are bounded to the south by the Monterey Bay Fault Zone. The younger Mio-Pliocene sediments of the Monterey and Purisima Formations are bounded by the Monterey Bay and San Gregorio Fault Zones. The Monterey Canyon contact between the Monterey Formation and Salinian granite must dip steeply.

Within the Monterey Canyon, Salinian granite that correlates isotopically (Rb/Sr) with granites at Tomales Bay, is exposed continuously on the south side of Monterey Canyon and east side of Carmel Canyon. Limited exposures from compressional (?) ridges on the west side of Carmel Canyon are all carbonatecemented Cretaceous-Paleocene sandstones and siltstones. No outcrops of older Franciscan Formation have been identifed in situ. We suggest that the Soquel canyon volcanism was associated with the tectonic opening of Monterey Bay during the Tertiary plate reorganization. The isotopic correlation of the Monterey Canyon granites and those at Tomales Bay requires 150 km offset along the San Gregorio Fault Zone in the past 11 my.

AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California