COMPOSITIONAL HETEROGENEITY OF THE JOSEPHINE MOUNTAIN INTRUSION

Our study assessed the mineralogy of a sample of the Josephine Mountain Intrusion (JMI) collected at the Hidden Springs Picnic Area in the San Gabriel Mountains, CA. The JMI was mapped as quartz monzonite by prior studies (Minch et al., 2002) yet our sample proved to be a peraluminous syenogranite. The compositional heterogeneity we observed in this intrusion suggests it was not emplaced as a large, convecting, well-mixed diapir, but rather in an incremental fashion, perhaps reflecting changing conditions at the magma’s source.