PALEOMAGNETISM, PALEOGEOGRAPHIC ORIGINS, AND UPLIFT HISTORY OF THE COAST RANGE OPHIOLITE AT MOUNT-DIABLO, CALIFORNIA

Divergent paleogeographic origins have been proposed for the Coast Ran ge ophiolite of western California which are testable using paleomagne tic methods. Paleomagnetic data for Middle Jurassic pillow lavas and d iabase sills of the Coast Range ophiolite at Mount Diablo, northern Ca lifornia, indicate that they contain two components of remanent magnet ization. The characteristic directions have normal and reversed polari ties and apparently are carried by Ti-poor magnetite. This magnetizati on is inferred to have been acquired during emplacement and seafloor a lteration at an ancient spreading ridge. The paleolatitude calculated from its structurally corrected mean direction is 20 degrees N +/- 9 d egrees and agrees with the expected direction for stable North America ; this result is also consistent with the concordant paleolatitude (32 degrees N +/- 8 degrees) recently determined for Upper Jurassic Coast Range ophiolite at Stanley Mountain in southern California. In additi on, clockwise vertical axis rotation of Mount Diablo (143 degrees +/- 11 degrees) is indicated by the characteristic magnetization direction . An overprint component is inferred to have been acquired during upli ft of Mount Diablo since the Miocene.