Petrology and Geochemistry of the Late Eocene Harrison Pass Pluton, Ruby Mountains Core Complex, Northeastern Nevada

Abstract

which suggest a single mixing event before emplacement in the upper The late Eocene Harrison Pass pluton was emplaced in the crust. Late-stage activity consisted of three pulses of monzogranitic transition zone between the infrastructure and suprastructure of the magma plus sparse mafic dikes. The largest and youngest of these Ruby Mountains core complex. Emplacement was at >3 kbar pulses, the two-mica monzogranite of Green Mountain Creek, is pressure and was in two stages: early stage tonalitic to monzogranitic distinct from all other units in the presence of restitic enclaves, low magmas, followed by late-stage monzogranites and mafic dikes. Nd, and high initial Sr/Sr. Pod-like bodies of leucocratic biotite The early stage began with emplacement of biotite ± hornblende ± amphibole monzogranite and sheets and dikes of leucocratic granodiorite of Toyn Creek, followed by the biotite monzogranite of two-mica monzogranite make up the other late-stage granites. These Corral Creek. Quenched equivalents of these units are preserved as rocks display deep negative Eu anomalies and show wide, nonporphyritic dikes in the roof. Leucocratic monzogranite that forms systematic concentrations of high field strength elements; however, cupolas in the roof zone represents the product of fractional crystheir isotopic compositions are identical to those of the early stage tallization of the early magmas. Al-in-hornblende barometry and rocks. They are thought to be small melt fractions of the lower to the presence of magmatic epidote suggest that early stage magmas middle crust. Their elemental compositions are thought to result resided at a pressure of >5−6 kbar before emplacement in the from the effects of residual plagioclase and accessory minerals. The upper crust. Compositional variation in the Toyn Creek and Corral variable and non-systematic isotopic compositions of all granitic Creek units is essentially linear, and can be explained by mixing units in the pluton suggest a heterogeneous source region, such as of a tonalitic end member with a monzogranitic end member such the Proterozoic Mojave province. as evolved samples of the monzogranite of Corral Creek. The tonalitic end member was itself a hybrid that formed by interaction