HR: 1340h
AN: GP33A-0106    [Abstracts]
TI: Simultaneous Clockwise and Counterclockwise Rotation Along the Eastern California Shear Zone at the Coso Range, California
AU: * Pluhar, C J
EM: cpluhar@pmc.ucsc.edu
AF: University of California, Santa Cruz, Earth Science Dept. 1156 High St., Santa Cruz, CA 95064-1077 United States
AU: Coe, R S
EM: rcoe@pmc.ucsc.edu
AF: University of California, Santa Cruz, Earth Science Dept. 1156 High St., Santa Cruz, CA 95064-1077 United States
AU: Monastero, F C
EM: cpluhar@es.ucsc.edu
AF: China Lake Naval Air Warfare Center, Geothermal Program Office, China Lake, CA 93555-6001 United States
AB: The Coso Range, California lies in a releasing step-over of the westernmost strand of the dextral Eastern California Shear Zone (ECSZ). Previous paleomagnetic studies on c.a. 3 Ma lavas of Wild Horse Mesa, within the Coso Range, demonstrate small-magntiude (12.0°±4.6°) clockwise vertical-axis rotations since emplacement of these rocks. Seismogenic, slickenline, and GPS strain data in the same region indicate a present-day rotation rate consistent with lava paleomagnetism results. However, paleomagnetism of lake beds of the White Hills, south of Wild Horse Mesa, yields a (reversed-polarity) mean direction of declination = 171.8°, inclination = -27.8°, κ = 12.3, and α₉₅ = 7.5° for n = 34 samples. Thus, White Hills have rotated counterclockwise 8.2°±8.2° since the sediments were deposited around 1 Ma. Although not significant at 95% confidence, this rotation is significant at any lesser confidence level and therefore indicates counterclockwise rotation. The opposite sense of rotation between White Hills and Wild Horse Mesa is understandable by the differing fault orientation and deformation styles between the two locales. The White Hills are an anticline within the larger-scale releasing bend of the ECSZ. Faults in the White Hills are generally oriented north-south to northwest-southeast. On the other hand the Wild Horse Mesa forms a transtentional basin with widespread north-south to northeast-southwest oriented normal faults. These differing fault orientations, probably intimately related to the local transpression and transtension within the two areas, respectively, results in simultaneous rotation of opposite sense due to an invariant far-field strain.
DE: 1145 Tephrochronology (8455)
DE: 1520 Magnetostratigraphy
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8111 Continental tectonics: strike-slip and transform
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005