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Comparison of granitic intrusions in the Pelona and Orocopia Schists, southern California

December 29, 2008

Dating of some small plutons in the San Gabriel and Chocolate Mountains, southern California, yields Miocene K-Ar ages. A single granodiorite pluton that has been segmented by branches of the San Jacinto fault intrudes the Pelona Schist and yields ages of 14.0 to 18.6 million years. Several quartz monzonite plutons in the Chocolate Mountains, 235 kilometers to the southeast and on the opposite side of the San Andreas fault, yield ages ranging from 20.0 to 23.4 m.y. At least one pluton in the Chocolate Mountains intrudes the Orocopia Schist, a probable equivalent of the Pelona Schist. Chemical, modal, textural, mineralogical, and apparent K-Ar age differences suggest that the two groups of plutons are not offset parts of a single body, but the differences do not preclude the two groups from being related in a general way.

Citation Information

Publication Year 1977
Title Comparison of granitic intrusions in the Pelona and Orocopia Schists, southern California
Authors Fred K. Miller, Douglas M. Morton
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Research of the U.S. Geological Survey
Index ID 70164409
Record Source USGS Publications Warehouse