| Blanca Peak |
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Geology (Blanca Peak)Title: Blanca Peak Geology Entered by: rockdoc53 Added: 10/19/2010, Last Updated: 10/19/2010 Sources: Johnson, B.R. and Bruce, R.M., 1991, Reconnaissance geologic map of parts of the Twin Peaks and Blanca Peak Quadrangles, Alamosa, Costilla, and Huerfano counties, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-2169 Blanca, Ellingwood and Little Bear peaks are part of a granitic batholith formed over 1.7 billion years ago (Early Proterozoic). Blanca Peak is composed predominantly of metagabbro with tonalite gneiss on the eastern side. Metagabbro is a dark gray to very dark green, metamorphosed igneous rock of gabbroic composition, typically with phenocrysts of hornblende and plagioclase. Tonalite gneiss is a white to light gray green metamorphosed igneous rock of tonalite composition, typically 60% plagioclase, 30% quartz 2% potassium feldspar, and 8% percent mafic minerals altered to epidote, chlorite and muscovite. A few Miocene-Oligocene felsic dikes intrude the metagabbro near the summit. |
