Description
In the northern Sierra Nevada, California at a latitude of approximately 39 °N, are a series of plutonic rocks that make up the Emigrant Gap composite pluton. The southern part of the pluton consists ofAlaskan-type ultramafic to mafic rocks. In contrast, the bulk of the pluton consists mostly of a hornblende-biotite granodiorite unit that grades into a two-pyroxene diorite unit along the margms of the pluton. Assessment of field relationships along with petrographical and geochemical work of previously mapped plutonic rocks within the central portion of the Emigrant Gap composite pluton are reported here. Within the study area, a search for a contact separating twopyroxene diorite through granodiorite from hornblende-biotite granodiorite was unsuccessful. These rocks show petrographical and geochemical characteristics of the hornblende-biotite granodiorite unit. Combining the results presented here with those from previous work suggest that the central portion of the Emigrant Gap composite pluton is underlain by rocks of the hornblende-biotite granodiorite unit. Preliminary geochemical data suggest that hornblende-biotite granodiorite unit was derived from typical calc-alkaline magma within a volcanic arc setting.
