Abstract: Effects of Local Block Rotations on the Amount of Paleomagnetically Determined Tectonic Rotation of the Western Transverse Ranges

Marc J. Kamerling

Models proposed to explain the paleomagnetic results from the western Transverse Ranges (WTR) involve clockwise rotation of crustal blocks bounded by left-lateral strike-slip faults, all within the larger zone of distributed right-lateral transtension between the Pacific and North America plates. One consequence of these models is that internally, the clockwise rotating blocks are undergoing left-lateral shear. This suggests that counterclockwise rotation of domains within the WTR should be occurring. Thus, the paleomagnetically determined net rotation could be less than the actual amount of tectonic rotation. Evidence for rotation of blocks (on the order of 50 m to 1-2 km) within the WTR is common. Features such as dikes, fold axes, and outcrop patterns are observed to be rotated fro 10° to 35° counterclockwise across sets of faults. Models of block rotations suggest that counterclockwise rotations could be as much as 50° in limited areas. The net effect of local counterclockwise rotations could be to reduce the amount of apparent tectonic rotation by 20° or more. Thus, the actual amount of clockwise tectonic rotation of the WTR could be more like 95° to 120°. This would permit the WTR to be reconstructed to a position adjacent to coastal Orange County(?) and fully close the inner borderland.

AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994