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

State	Rhode Island
Name	Scituate Igneous Suite - alkali-feldspar granite
Geologic age	Devonian
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.
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.
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. https://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.
NGMDB product	NGMDB product page for 19719
Counties	Kent - Providence - Washington

State

Name

Scituate Igneous Suite - alkali-feldspar granite

Geologic age

Devonian

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.

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.

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.

https://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.

NGMDB product

NGMDB product page for 19719

Counties

Kent - Providence - Washington