State | Connecticut |
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Name | Ponaganset Gneiss |
Geologic age | Proterozoic Z? |
Lithologic constituents | Major
Metamorphic > GneissDark-gray, coarse-grained, porphyritic, well-foliated gneiss, composed of oligoclase, quartz, microcline (mostly as megacrysts up to 8 cm long), biotite, magnetite, and generally hornblende; also garnet and muscovite where hornblende is absent.
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Comments | Part of Eastern Uplands; Avalonian (Continental) Terrane; Avalonian Anticlinorium; Sterling Plutonic Group (Proterozoic Z?). Secondary unit description pet CT016. |
References | Rodgers, John, compiler, 1985, Bedrock Geological Map of Connecticut: Connecticut Geological and Natural History Survey, Hartford, Connecticut, 2 sheets, scale 1:125,000.Skehan, J.W. and Rast, Nicholas, 1990, Pre-Mesozoic evolution of Avalon terranes of southern New England, IN Socci, A.D., Skehan, J.W., and Smith, G.W., eds., Geology of the composite Avalon terrane of southern New England: Geological Society of America Special Paper, 245, p. 13-53. |
NGMDB product | |
Counties | New London - Windham |