PETROLOGY AND GEOCHEMISTRY OF MONUMENT PEAK PLUTON, WEAVERVILLE, CALIFORNIA

The Monument Peak pluton is a small (~3km²) pluton in the southeast Klamath Mountains Province, ~12 km northwest of Weaverville, California. We mapped the western margin of the pluton and completed petrologic and geochemical (XRF) analyses in order to establish the contact relationships and composition of the pluton and to determine the possible relationship of this pluton to recognized Klamath plutonic suites .

The Monument Peak pluton is composed of diorite and granodiorite; it intrudes amphibolite of the Salmon Hornblende Schist. Thin sections show pluton samples to be typically holocrystalline, medium to fine grained, and leucocratic; ~ 80% plagioclase and quartz, and the remaining 20% composed of biotite and hornblende. The pluton is calc-alkalic, and bulk composition plots in the diorite-granodiorite fields of total alkali silica diagram. Monument Peak pluton samples show a range of compositions that overlap with those of the late Jurassic Wooley Creek plutonic suite and those of the early Cretaceous tonalite-trondhjemite suite.