Scituate Igneous Suite - alkali-feldspar granite (RIDsa;0)

Scituate Igneous Suite - alkali-feldspar granite - Gray to pink, medium- to coarse-grained, porphyritic to subporphyritic alkali-feldspar granite (phenocrysts of perthite). Contains perthite, quartz, and accessory biotite, hornblende, and lesser riebeckite, aegerine, zircon, allanite, sphene, fluorite, and opaque minerals. Plagioclase is sparse to absent. Secondary muscovite, chlorite, and calcite. Ovoid clots of mafic and accessory minerals are locally prominent. Rock is a hypersolvus, mildly peralkaline granite. Fabric ranges from massive to locally lineated and foliated. Includes rock mapped formerly in part as Scituate Granite Gneiss, Cowesett Granite, and perthitic Cowesett Granite.

State	Rhode Island
Name	Scituate Igneous Suite - alkali-feldspar granite
Geologic age	Devonian
Original map label	Dsa
Comments	Part of Esmond-Dedham Subterrane (West Bay Area) The name Scituate Granite Gneiss is no longer appropriate because the type Scituate of Quinn (1971) at Scituate, RI, has been shown by Hermes and others (1981) and Hermes and Zartman (1985) to be Middle Devonian, based on isotopic age of 373 +/-7 Ma; it is part of an unnamed Devonian alkalic suite. Scituate of type area in central RI described by Quinn (1971) is here renamed Scituate Granite and assigned a Middle Devonian age (Wones and Goldsmith, 1991) per RI004. Per printed map: age of rock based on radiometric data from RI005 and RI009.
Primary rock type	alkali-granite (alaskite)
Secondary rock type
Other rock types
Lithologic constituents	Major Igneous > Plutonic > Granitic > Alkali-feldspar-graniteGray to pink, medium- to coarse-grained, porphyritic to subporphyritic alkali-feldspar granite (phenocrysts of perthite). Contains perthite, quartz, and accessory biotite, hornblende, and lesser riebeckite, aegerine, zircon, allanite, sphene, fluorite, and opaque minerals. Plagioclase is sparse to absent. Secondary muscovite, chlorite, and calcite. Ovoid clots of mafic and accessory minerals are locally prominent. Rock is a hypersolvus, mildly peralkaline granite. Fabric ranges from massive to locally lineated and foliated.
Map references	Hermes, O.D., Gromet, L.P., Murray, D.P., Hamidzada, N.A., 1994, Geologic Map of Rhode Island, file name = bedrock_shp.zip (870kb) obtained from Rhode Island Geographic Information System, http://www.edc.uri.edu/rigis-spf/Statewide/state.html#geology , shapefile or interchange file, scale 1/100,000. [http://www.edc.uri.edu/rigis-spf/Statewide/state.html#geology]
Unit references	Hermes, O.D. (comp.), Gromet, L.P. (comp.), Murray, D.P. (comp.), Hamidzada, N.A., Skehan, J.W., and Mosher, S., 1994, Bedrock geologic map of Rhode Island: Rhode Island Map Series No. 1, Kingston, Rhode Island, scale 1: 100,000. Wones, D.R. and Goldsmith, Richard, 1991, Intrusive rocks of eastern Massachusetts, Chapter I, IN Hatch, N.L., Jr., ed., The bedrock geology of Massachusetts: U.S. Geological Survey Professional Paper, 1366-E-J, p. I1-I61. [http://pubs.er.usgs.gov/publication/pp1366EJ] Hermes, O.D., and Zartman, R.E., 1985, Late Precambrian and Devonian plutonic terrane within the Avalon Zone of Rhode Island: Geological Society of America Bulletin, v. 96, p. 272-282. Hermes, O.D., Gromet, L.P., and Zartman, R.E., 1981, Zircon geochronology and petrology of plutonic rocks in Rhode Island, p. 315-338: in Boothroyd, J.C., and Hermes, O.D., editors, Guidebook to Field Studies in Rhode Island and Adjacent Areas: 73rd New England Intercollegiate Geological Conference, University of Rhode Island, Kingston, 383p.
Geographic coverage	Kent - Providence - Washington