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Paleomagnetism, paleogeographic origins, and uplift history of the Coast Range ophiolite at Mount Diablo, California

January 1, 1998

Divergent paleogeographic origins have been proposed for the Coast Range ophiolite of western California which are testable using paleomagnetic methods. Paleomagnetic data for Middle Jurassic pillow lavas and diabase sills of the Coast Range ophiolite at Mount Diablo, northern California, indicate that they contain two components of remanent magnetization. The characteristic directions have normal and reversed polarities and apparently are carried by Ti-poor magnetite. This magnetization is inferred to have been acquired during emplacement and seafloor alteration at an ancient spreading ridge. The paleolatitude calculated from its structurally corrected mean direction is 20??N ?? 9?? and agrees with the expected direction for stable North America; this result is also consistent with the concordant paleolatitude (32??N ?? 8??) recently determined for Upper Jurassic Coast Range ophiolite at Stanley Mountain in southern California. In addition, clockwise vertical axis rotation of Mount Diablo (143?? ?? 11??) is indicated by the characteristic magnetization direction. An overprint component is inferred to have been acquired during uplift of Mount Diablo since the Miocene.