GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 347-32
Presentation Time: 9:00 AM-6:30 PM


POLON, Casey K.1, PLUHAR, Chris J.1, GLEDHILL, Trevor A.1, TRAYLER, Robin2, CROWLEY, Jim2, WARD, Preston1, SCHMITZ, Mark2, NGO, My My1, CARLSON, Chad W.3 and LARSEN, Mark T.1, (1)Earth and Environmental Sciences, Fresno State University, 2576 East San Ramon Ave, M/S ST24, Fresno, CA 93740, (2)Department of Geosciences, Boise State University, Boise, ID 83725-1535, (3)Nevada Bureau of Mines and Geology, University of Nevada, Reno, NV 89557,

Geochemical, petrological, and geochronologic studies of the ~83 Ma Coso and Golden Bear quartz monzonite dikes and corresponding ~102 Cactus Flat and Independence Ma host plutons suggested 65 km of syn- or post-Laramide dextral offset in the southern Owens Valley, CA. This proposed dextral offset agrees with results for older piercing points in the northern Owens Valley, including: 1) offset of the 0.706 Sr isotope isopleth, 2) offset of Devonian submarine channels, and 3) offset of the Independence dike swarm. However, our recent studies weaken the dike correlation hypothesis. Data from the single, continuous Golden Bear dike show normal paleomagnetic polarity, while samples from the numerous, discontinuous Coso dikes show mixed polarity both within dikes and between them. Additionally, other normal polarity dikes in the Cottonwood Lakes area have been identified since the previous studies, and provide an alternate correlation to the Coso Dikes, as well evidence that diking may have been more widespread at this time, rather than just at the location of the Golden Bear Dike. Previous U-Pb geochronology of the Coso and Golden Bear dikes yielded ages of ~83 Ma, yet these ages were accompanied by large errors. Our preliminary U-Pb LA-ICP-MS zircon dates show that all of the mentioned dikes were emplaced around the same time, opening up multiple hypotheses to explain their emplacement, with the Golden Bear-Coso correlation being only one of them. These results substantially weaken that correlation conclusion and the 65km of post 83 Ma dextral offset that it required.