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Devonian Tomhegan Formation Kineo Rhyolite member tuffs and volcaniclastic rocks

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Devonian Tomhegan Formation Kineo Rhyolite member tuffs and volcaniclastic rocks
State Maine
Name Devonian Tomhegan Formation Kineo Rhyolite member tuffs and volcaniclastic rocks
Geologic age Devonian
Comments Revised as a member of the Tomhegan formation (new). Consists of blue-gray, bone-white-weathering, massive, conchoidally fracturing felsite with quartz and feldspar phenocrysts; blue-gray, greenish-white-weathering, irregularly fracturing felsite with garnet and white feldspar phenocrysts; dark-blue-gray, greenish-white to light-gray-weathering tuff; blue-gray, chalky-white-weathering tuff containing felsite and pumice fragments and fine-grained volcanic debris (devitrified shards); rhyolitic felsite pebble conglomerate; and flow breccia resembling the felsite but containing numerous irregular felsite fragments in a matrix of same material. Thickness ranges from 0 to 4,000 ft. Underlies main part of Tomhegan formation; overlies Tarratine formation. Report includes geologic map and correlation chart. (ME003) Revised to include rocks previously mapped as both Heald Mountain Rhyolite and Kineo Volcanic Member of Boucot and Heath (1969). Exposed in Long Pond and Pierce Pond 15-min quads. Consists of weakly metamorphosed rhyolite ash-flow tuff, flows, domes, volcanic breccia, grit, and conglomerate as well as associated hypabyssal, garnet-bearing felsic intrusive rocks. Separately mapped intrusive garnet rhyolite in Tomhegan Formation, previously mapped as both unnamed garnet rhyolite and garnet rhyolite of the Kineo Volcanic Member by Boucot and Heath (1969), is now considered to be equivalent to Kineo. (ME004) Unit description from USGS GEOLEX website (ME078). W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite GS - Greenschist facies Protolith T - Rhyolitic volcanic rocks
Primary rock type rhyolite
Secondary rock type
Other rock types
Lithologic constituents
Major
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Pyroclastic, tuff)W - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite GS - Greenschist facies Protolith T - Rhyolitic volcanic rocks
Map references
Digital bedrock data downloaded from Maine Office of GIS in September 2005 from http://apollo.ogis.state.me.us/catalog/catalog.asp?state=2&extent=cover#bedrock Bedrock units table (publication date 11/15/2002) downloaded from same site. Permission to redistribute these data granted by Dr. Robert Marvinney, State Geologist of Maine, in September 2006.
Unit references
Osberg, P. H., Hussey, A.M., and Boone, G. M., 1985, Bedrock geologic map of Maine: Maine Geological Survey, Dept. of Conserv., scale 1:500,000.
Boucot, A.J., 1961, Stratigraphy of the Moose River synclinorium, IN Contributions to general geology, 1959: U.S. Geological Survey Bulletin, 1111-E, p. E153-E188.
Moench, R.H., Boone, G.M., Bothner, W.A., Boudette, E.L., Hatch, N.L., Jr., Hussey, A.M., III, Marvinney, R.G. and Aleinikoff, J.N., 1995, Geologic map of the Sherbrooke-Lewiston area, Maine, New Hampshire, and Vermont, United States, and Quebec, Canada: U.S. Geological Survey Miscellaneous Investigations Series Map, I-1898-D, 56 p., 2 sheets, scale 1:250,000, Prepared in cooperation with the Maine Geological Survey and the New Hampshire Geological Survey.
Boucot, A.J., 1969, Geology of the Moose River and Roach River synclinoria, northwestern Maine: Maine Geol. Surv., Bull. 21, 123 p.
USGS Geologic Names Lexicon (GEOLEX)
Counties Somerset