Westerly Granite

Light-gray, pink-weathering, fine-grained, massive, aplitic granite, composed of oligoclase or albite, quartz, and K-feldspar, with minor biotite and accessory muscovite, magnetite, allanite, and sphene.
State Connecticut
Name Westerly Granite
Geologic age Permian
Lithologic constituents
Major
Igneous > Plutonic > Granitic > GraniteLight-gray, pink-weathering, fine-grained, massive, aplitic granite, composed of oligoclase or albite, quartz, and K-feldspar, with minor biotite and accessory muscovite, magnetite, allanite, and sphene.
Comments Part of Eastern Uplands; Avalonian (Continental) Terrane. Narragansett Pier Granite and Westerly Granite, which occur in both the Hope Valley and Esmond-Dedham terranes (the Avalon Superterrane of this report) are here assigned to the Narragansett Plutonic Suite (new name). Outcrops trend East-West along the coasts of RI and CT. Similar rocks have also been recognized in southeastern MA. According to Zartman and Hermes (1987), the granites are essentially coeval. The Westerly, though dated at 276+/-7 Ma (U/Pb)), may slightly postdate the Narragansett Pier (U/Pb 273+/-2 Ma) based on apparent intrusive contacts. The Westerly occurs mainly as dikes. Described as gray with tints of blue to pink, equigranular and fine-grained calc-alkaline quartz monzonite to granodiorite. Consists mainly oligoclase, microcline, quartz, and biotite with minor muscovite (Skehan and Rast, 1990) per CT014.
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