Trap Falls Formation

(May be equivalent in part to Golden Hill Schist) - Gray to silvery, partly rusty weathering, medium-grained generally well layered schist, composed of quartz, sodic plagioclase, biotite, muscovite, and garnet, locally with sillimanite or kyanite, interlayered with two-mica gneiss and granulite and with amphibolite.
State Connecticut
Name Trap Falls Formation
Geologic age Middle or Lower Ordovician
Lithologic constituents
Major
Metamorphic > SchistGray to silvery, partly rusty weathering, medium-grained generally well layered schist, composed of quartz, sodic plagioclase, biotite, muscovite, and garnet, locally with sillimanite or kyanite.
Minor
Metamorphic > Gneissinterlayered with two-mica gneiss and granulite
Metamorphic > Amphibolite
Metamorphic > Granuliteinterlayered with two-mica gneiss and granulite
Comments Part of Central Lowlands; Iapetus (Oceanic) Terrane - Connecticut Valley Synclinorium; Hartland Belt. Part of Hawley Formation and equivalent formations (includes Trap Falls and Cobble Mountain Formations) (Middle Ordovician). The staurolite-kyanite-grade schists of the Trap Falls Formation contain reversely discordant xenoblastic monazites with 207Pb/235U ages ranging from 385 to 376 Ma and concordant to normally discordant idioblastic monazites that grew approximately 395 Ma. These ages probably represent the range of the Acadian metamorphic thermal peak (Sevigny and Hanson, 1993) per CT007.
References

Rodgers, John, compiler, 1985, Bedrock Geological Map of Connecticut: Connecticut Geological and Natural History Survey, Hartford, Connecticut, 2 sheets, scale 1:125,000.

Sevigny, J.H. and Hanson, G.N., 1993, Orogenic evolution of the New England Appalachians of southwestern Connecticut: Geological Society of America Bulletin, v. 105, no. 12, p. 1591-1605.

NGMDB product
Counties Fairfield - Hartford - New Haven