2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 7
Presentation Time: 8:00 AM-4:45 PM

Lithologic Variation of Proterozoic Rocks in the San Gabriel Mountains, Wrightwood, California


DILLON, Jessica-Ann M., Department of Geological Sciences, California State University Northridge, 18111 Nordhoff St, Northrige, CA 91330-8266 and MIRANDA, Elena A., Department of Geological Sciences, California State University at Northridge, 18111 Nordhoff Street, Northridge, CA 91330-8266, jmd16034@csun.edu

The Transcontinental Proterozoic province (1.8-1.6 Ga) extends into the Mojave desert region of eastern California, but Mesozoic and Cenozoic tectonism has made the interpretation of Mojave and Yavapai province boundaries difficult. Rocks of presumed Proterozoic age are exposed in the San Gabriel Mountains to the east of the San Andreas Fault near Wrightwood, California, but their province affiliation remains unknown. Based on reconnaissance field mapping of rocks exposed at Table Mountain, we document a sequence of mafic gneisses, intrusive rocks and calc-silicate rocks. We observe biotite-rich mafic gneiss with foliation that dips moderately to the northeast, and alternating sequences of quartzites and marbles with relict bedding planes that dip moderately to the northeast. Garnet-bearing granites are exposed in sills parallel to relict bedding planes and in cross-cutting dikes. We observe diopside- and actinoliteĀ–bearing steeply-dipping dikes that cut across the granites and calc-silicate metasediments. A similar sequence of rocks is associated with the layered gneisses of the Mojave province, suggesting that this region of the San Gabriel Mountains may be affiliated with the Mojave province. In the future, U-Pb dating of detrital zircons from the quartzites and of igneous zircons from the granite may permit testing of this hypothesis.