65 km of Post-Cretaceous Offset Across Owens Valley, CA? Constraints Using Paleomagnetism

Details 65 km of Post-Cretaceous Offset Across Owens Valley, CA? Constraints Using Paleomagnetism 65 km of Post-Cretaceous Offset Across Owens Valley, CA? Constraints Using Paleomagnetism

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmgp44a..05p&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #GP44A-05

Other

1525 Paleomagnetism Applied To Tectonics: Regional, Global, 8011 Kinematics Of Crustal And Mantle Deformation, 9350 North America, 9604 Cenozoic, 9610 Cretaceous

Scientific paper

Recent studies suggest that several pre-Cenozoic piercing points have been offset ~65 km along a cryptic structure sub-parallel to the Owens Valley, CA. These piercing points include: 1) Sr isotope 0.706 isopleth, 2) Permian and Triassic structural features of the White and Inyo Mountains, CA, 3) offset Independence Dike swarm, 4) offset Cretaceous dikes (c.a. 83 Ma) and plutons (c.a. 102 Ma) of the Sierra Nevada and Coso Range, CA. The present study aims to: 1) test the offset hypothesis on the Cretaceous dikes and leucogranites by comparing paleomagnetic results on the proposed offset rocks, and/or 2) if the proposed offset is found to be consistent with paleomagnetic data, to use the remanence results to examine kinematic behavior of the crust during and since offset. Preliminary results indicate that, where sampled at three localities, the c.a. 83 Ma dikes that are proposed to have been offset are of opposite paleomagnetic polarity on either side of the proposed offset. This result, if confirmed by additional sampling, would falsify the hypothesis of contemporaneity and thus original continuity and subsequent offset. On the other hand, if additional sampling demonstrates that dikes are of mixed polarity on either side of the proposed offset, then these data would constrain the age of dike emplacement to around the C34n-C33r boundary at 83.5±0.7 Ma. As expected, the c.a. 102 Ma leucogranites, emplaced during the Cretaceous long normal, both exhibit normal polarity. However, these rocks show a discordance in remanence direction which is likely the result of differential tilt and/or vertical axis rotation of the sampled units. Vertical axis rotation may be likely, as suggested by dike strike variations. A baked contact test on the sampled rocks of the Coso Range confirms that those units retain a primary magnetization.

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