Geochemistry and petrology of Triassic granitoids of the Sierra Nevada batholith, California and Nevada

The Triassic Scheelite intrusive sequence is studied here in relation to geochemical and petrologic constraints found in earlier studies. The Triassic granitoids show chemical composition trends in the north-to-south direction that are similar to those found across the entire batholith in the west-to-east direction in earlier studies. An analysis of 32 samples from the Triassic granitoids shows that potassium increases and sodium decreases from north to south. The parent magma for the Triassic granitoids is shown to be an andesitic melt and the existing intrusions were evolved through fractionation of plagioclase and amphibole mineral assemblages. The northern portion of the Triassic sequence is shown to be simpler in chemical composition than the southern portion. The Triassic granitoids are shown to be different from the Jurassic granitoids but similar to those of the Cretaceous. The genetic models of batholithic rocks which best fit these data are those which allow for varying source materials.