Author : Michael B. Walen
Publisher :
Page : 0 pages
File Size : 18,45 MB
Release : 1973
Category : Geochemistry
ISBN :
The study area extends from Phantom Creek to Crystal Creek, a distance of approximately 10 miles along the Colorado River. The units exposed are the Precambrian Vishnu Schist granitic to granodioritic units in Phantom Canyon, Trinity Canyon, and near Crystal Creek, and pegmatites and aplites. The Vishnu Schist is composed mostly of quartzo-feldspathic schists. The assemblage quartz-oligoclase-muscovite-biotite-sillimanite-K-feldspar indicates metamorphic conditions in the upper amphibolite facies between Phantom Creek and Mile 95. Between Mile 95 and Crystal Creek, assemblages indicate lower amphibolite to greenschist facies conditions. The Phantom Granitic Complex consists of granodioritic and quartz monzonitic units. The presence of a contact breccia, rotated xenoliths, and cross-cutting apophyses indicate the pluton is intrusive. The rocks cluster around the 3 kb cotectic in the Ab-Or-Qtz system which suggests a magmatic origin. The Trinity Gneiss is a homogeneous granodioritic gneiss. Intercalated layers of quartzite and schist and calc-silicate lenses support a meta-sedimentary origin. Chemical data suggest that the biotite-rich layers are meta-sedimentary but the granitic layers plot along cotectic troughs and may represent rhyolitic or rhyodacitic flows. The Crystal Creek Granite is a post-tectonic, epidoterich granitic rock. Field evidence suggest the pluton is intrusive. Quartz and schistose inclusions and the unusual mineralogical and chemical composition suggest the granite has been contaminated. Late low grade metamorphism has resulted in dominantly metamorphic textures. The Vishnu Schist has been cut by pegmatite and aplite dikes. Apophyses and cross-cutting relationships indicate the pegmatite/aplites are intrusive. Chemical data clusters around the cotectic minimums in the Ab-0r-Qtz-H20 system suggesting a magmatic source. Large crystals and quartz cores suggest the pegmatites are of hydrothermal origin.