PALEOMAGNETIC CONSTRAINTS ON THE MOVEMENT HISTORY OF SALINIA (CALIFORNIA)

The Salinian terrane of coastal California, strikingly out of place in its present position, is probably a fragment of the Cordilleran arc. Although its closest possible point of origin is the southern Sierra Nevada, geologic data suggest this is not an adequate reconstruction and paleomagnetic studies indicate an origin far to the south. Paleomagnetic work reported here helps define the limits and movement history of Salinia.;Paleomagnetic evaluation of three units of the Point Arena terrane provides a history of the terrane's progressive motion from Cretaceous(?) to early Miocene time. The paleomagnetic direction of spilitic basalts at the structural base of the section (D = 193, I = 10) indicates that they formed in very low latitudes. Paleocene and Eocene rocks have a direction that is significantly clockwise of and shallower than their expected direction, but less anomalous than that of the spilites. Earliest Miocene basalts show no evidence of significant rotation or poleward transport.;As a test of the cross-San Andreas fault correlation of the Butano and Point of Rocks Sandstones, the paleolatitude of the Butano Sandstone west of the fault was determined by paleomagnetic analysis of azimuthally unoriented oil well cores. When motion on Neogene right lateral faults is considered, the mean paleolatitude, 34.6(DEGREES), is not significantly different from that expected, confirming the correlation of the Butano and Point of Rocks Sandstones.;At least part of Salinia was in southern California by the early Eocene. The rotation observed in the southern Sierra Nevada may be related to Salinia's passage. The Point Arena terrane has a movement history different from that of central Salinia.;The upper Cretaceous Bear Valley Springs pluton in the southernmost Sierra Nevada yields a mean direction D = 22(DEGREES), I = 56(DEGREES) that differs significantly from both the expected Cretaceous direction and that found in the central Sierra Nevada, and suggests that the pluton has rotated clockwise about 45(DEGREES) about a steep axis. Lower miocene volcanic and sedimentary rocks overlie the pluton and have a mean direction D = 354(DEGREES), I = 64(DEGREES) that does not differ significantly from the expected Miocene direction, constraining rotation of the pluton to occur between about 80 and 20 m.y.b.p.