The Marion Peak 15-minute quadrangle includes about 620 km2 on the west slope of the Sierra Nevada in Fresno County, California, between 36°45' and 37°00' N. latitude and 118°30' and 118°45 W. longitude. This report supplements the geologic map of the Marion Peak quadrangle by providing modal and chemical analyses of the granitic and volcanic rock samples.
Granitic rocks of the batholith underlie 95 percent of the quadrangle area. Most of the remaining area is underlain by septa of pre-batholithic metamorphosed sediments and volcanic rocks which occur between the individual granitic masses. Cenozoic volcanic rocks underlie a small area, and they include an eroded dacitic volcanic center and scattered erosional remnants of basaltic lava flows.
About 300 samples of typical plutonic and volcanic rocks were collected during the course of geologic mapping; of these, 30 granitic, 2 metavolcanic, and 9 Cenozoic volcanic rocks were chemically analyzed for their major elements, and most were also analyzed for selected trace elements. In addition, 178 samples of granitic rocks were analyzed modally for the volume percent of their constituent minerals. Measurements of specific gravity and magnetic susceptibility are also included.
The average chemical composition of the granitic rocks in the quadrangle, estimated from the analyzed samples, is a silicic granodiorite that contains 69.2 weight percent SiO2.
|Title||Marion Peak quadrangle, Fresno County, California— Analytic data|
|Authors||James Gregory Moore|
|Publication Subtype||USGS Numbered Series|
|Record Source||USGS Publications Warehouse|