PALEOMAGNETISM OF THE MONTEREY FORMATION IN THE WESTERN TRANSVERSE RANGES, CALIFORNIA (TECTONICS, ROCK MAGNETISM)

Dolomites and limestones in the Monterey Formation generally possess either a stable primary magnetic remanence acquired prior to Plio-Pleistocene folding, or a stable secondary magnetic remanence acquired subsequent to Plio-Pleistocene folding. The primary remanence is carried by detrital magnetite, whereas the secondary remanence is carried by authigenic magnetite (+OR-) hematite.;Four additional widely separated stratigraphic sections (26 beds, 159 samples) of the upper Monterey Formation were sampled in the Santa Ynez Range. The clockwise-deflected magnetic declinations observed in these sections (mean 31 (+OR-) 16(DEGREES)) is interpreted to be largely the result of post-Miocene tectonic rotation of the western Santa Ynez Range.;Paleomagnetic data collected from throughout the western Transverse Ranges (an additional 38 beds, 242 samples) suggests that: (1) The clockwise-deflected magnetic directions are due to tectonic rotation of large crustal blocks (with the dimensions of the present mountain ranges) rather than to local block rotations; (2) The northern boundary of coherent tectonic rotation within the western Transverse Ranges is the Santa Ynez River fault; and (3) The total amount of right-lateral strike-slip predicted for the NW-trending faults in the Coast Ranges from the amount of tectonic rotation in the Santa Ynez Range is in agreement with geological estimates of displacements on these faults (200 km).;Palinspastic reconstructions of southern California for the early, middle, and late Miocene are proposed, based on the Luyendyk et al. (1980) hypothesis for crustal rotation, geological constraints, and the available paleomagnetic data.;A paleomagnetic investigation was conducted on dolomite beds in five stratigraphic sections of the middle and upper Miocene Monterey Formation exposed along the coastline between Santa Barbara and Point Conception (42 beds, 290 samples). Dolomites 14.8 to 15.8 m.y. old have a mean magnetic declination of 92 (+OR-) 7(DEGREES), whereas dolomites 8 to 12 m.y. old have a mean magnetic declination of 36 (+OR-) 7(DEGREES). The consistent upsection decrease in magnetic declination within these stratigraphic sections is attributed to a rapid 56 (+OR-) 10(DEGREES) clockwise rotation of the entire Santa Ynez Range between 15.2 and 10 m.y.b.p.