Little Cottonwood Ganodiorite with Mafic Enclave

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The Oligocene Little Cottonwood stock sits in the central Wasatch Mountains, Utah, roughly 30.5 to 29 million years ago, primarily composed of granodiorite, quartz monzonite, and granite with some mafic enclaves. "The Little Cottonwood stock is a felsic granitoid with an exposed area of 115 km2. When plotted on the total alkali-silica diagram, its composition clusters around the triple point between granite, granodiorite, and quartz monzonite. In the IUGS QAP diagram, it plots primarily as granodiorite, with fewer samples of quartz monzonite and granite." "Mafic enclaves hosted in the Little Cottonwood stock have the same mineral assemblage as the host rock, though with different modal abundances (Hanson, 1996). The enclaves are porphyritic-aphanitic; most enclaves are more than half poikilitic plagioclase, followed by biotite, hornblende, and small amounts of quartz and K-feldspar."