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Geologic units containing granitic gneiss

Alabama

Dadeville Complex; Camp Hill Granite Gneiss (Precambrian to Paleozoic)

Camp Hill Granite Gneiss - coarse to medium-grained foliated granite to quartz diorite (tonalite) gneiss, locally biotite-rich; locally contains thin amphibolite pods and lenses. Boundary between Rock Mills Granite Gneiss and Camp Hill Granite Gneiss arbitrarily defined.

Dadeville Complex; Rock Mills Granite Gneiss (Precambrian to Paleozoic)

Rock Mills Granite Gneiss - coarse to medium-grained biotite granite gneiss; locally includes thick bands of epidote and thin, small amphibolite bodies. Boundary between Rock Mills Granite Gneiss and Camp Hill Granite Gneiss arbitrarily defined.

Wacoochee Complex; Phelps Creek Gneiss (Precambrian to Paleozoic)

Phelps Creek Gneiss - quartz monzonite to granite gneiss in dikes and sheets with wide migmatite zones at contacts.

Connecticut

Foliated granitic gneiss (Devonian?)

Foliated granitic gneiss - Light-gray, coarse-grained, strongly to weakly foliated gneiss, composed of phenocrysts of K-feldspar in a groundmass of plagioclase, quartz, K-feldspar, and biotite, with accessory sillimanite and garnet.

Glastonbury Gneiss (Middle? Ordovician)

Glastonbury Gneiss - Gray, medium- to coarse-grained, massive to well-foliated granitoid gneiss composed of oligoclase, quartz, microcline, and biotite (as patches), also epidote and hornblende in many areas, commonly associated with layers of amphibolite; elsewhere minor muscovite and garnet.

Hope Valley Alaskite Gneiss (Proterozoic Z?)

Hope Valley Alaskite Gneiss - Light-pink to gray, medium- to coarse-grained, locally porphyritic, variably lineated and foliated alaskitic gneiss, composed of microcline, quartz, albite or oligoclase, and minor magnetite, and locally biotite and muscovite. Lineation formed by rods of quartz. Locally contains quartz-sillimanite nodules.

Light House Gneiss (Proterozoic Z?)

Light House Gneiss - Light-pink or gray to red, medium-grained, generally well foliated granitic gneiss, composed of K-feldspar, oligoclase, quartz, biotite, and magnetite, with local muscovite but no garnet.

Maromas Granite Gneiss (Devonian?)

Maromas Granite Gneiss - Light-gray to buff, medium- to fine-grained granitic gneiss, composed of quartz and microcline with minor plagioclase and biotite. Central body is massive, but outlying strips are foliated and have accessory hornblende or garnet. Massive parts may be young anatectic intrusive rocks; foliated parts may include older felsic metavolcanic rocks belonging to unit Ochv. Pegmatite bodies are common in the vicinity.

New London Gneiss (Proterozoic Z?)

New London Gneiss - New London consists of a layered facies and a massive facies. Layered facies described as alternating layers of light-colored biotite-quartz-plagioclase gneiss and amphibolite. Massive facies described as a granodiorite gneiss with a uniform texture, grain size, and color. Contains shiny black biotite plates and distinctive magnetite grains. New London consists of a layered facies and a massive facies. Layered facies described as alternating layers of light-colored biotite-quartz-plagioclase gneiss and amphibolite. Massive facies described as a granodiorite gneiss with a uniform texture, grain size, and color. Contains shiny black biotite plates and distinctive magnetite grains (Skehan and Rast, 1990).

Ordovician? granitic gneiss (Middle Ordovician?)

Ordovician? granitic gneiss (including local terms Ansonia, Mine Hill, "Tyler Lake," "Siscowit") - White, light-gray, buff, or pink, generally foliated granitic gneiss, composed of sodic plagioclase, quartz, microcline, muscovite, and biotite, and locally garnet or sillimanite. Commonly contains numerous inclusions or layers of mica schist and gneiss.

Ordovician? granitic gneiss (Middle Ordovician?)

Ordovician? granitic gneiss (including local terms Ansonia, Mine Hill, "Tyler Lake," "Siscowit") - White, light-gray, buff, or pink, generally foliated granitic gneiss, composed of sodic plagioclase, quartz, microcline, muscovite, and biotite, and locally garnet or sillimanite. Commonly contains numerous inclusions or layers of mica schist and gneiss.

Pink granitic gneiss (Proterozoic Y)

Pink granitic gneiss - Light-pink to gray, medium- to coarse-grained, foliated but generally massive or poorly layered granitic gneiss, composed of quartz, microcline, oligoclase, and either biotite or muscovite or both, also locally amphibole or epidote.

Plainfield Formation plus Potter Hill Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian)

Plainfield Formation plus Potter Hill Granite Gneiss plus Narragansett Pier Granite - Plainfield Formation - Interlayered light-gray, thin-bedded quartzite, in places with feldspar, mica, graphite, or pyrite, light- to medium-gray gneiss composed of quartz, oligoclase, and biotite (rarely microcline), medium- to dark-gray schist composed of quartz, oligoclase, biotite, sillimanite, and garnet, dark-gray or green gneiss composed of plagioclase, quartz, biotite, and hornblende (commonly with diopside), amphibolite, diopsite-bearing quartzite, and calc-silicate rock. In places contains quartz-sillimanite nodules. Potter Hill Granite Gneiss - Light-pink to gray, tan-weathering, fine- to medium-grained, rarely porphyritic, well-foliated (not lineated) granitic gneiss, composed of microcline, quartz, oligoclase (or albite), biotite, and magnetite, minor muscovite, and local garnet. Narragansett Pier Granite - Pink to red, medium- to coarse-grained (commonly pegmatitic), generally massive (not gneissic) granite, composed of microcline, oligoclase, quartz, and biotite, and accessory muscovite and magnetite. Considerable associated pegmatite.

Plainfield Formation plus Stony Creek Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian)

Plainfield Formation - Interlayered light-gray, thin-bedded quartzite, in places with feldspar, mica, graphite, or pyrite, light- to medium-gray gneiss composed of quartz, oligoclase, and biotite (rarely microcline), medium- to dark-gray schist composed of quartz, oligoclase, biotite, sillimanite, and garnet, dark-grey or green gneiss composed of plagioclase, quartz, biotite, and hornblende (commonly with diopside), amphibolite, diopside-bearing quartzite, and calc-silicate rock. In places contains quartz-sillimanite nodules. Stony Creek Granite Gneiss - Red to pink, unevenly medium to very coarse grained, variably foliated granite or granite gneiss, composed of oligoclase, K-feldspar, and quartz with minor biotite and magnetite, sporatic garnet (in foliated varieties), and local muscovite. Commonly contains granite and pegmatite of Narragansett Pier type (and probably age). In much of area both granites occur as innumerable veins penetrating other units or as larger bodies full of inclusions of those units, which can be mapped through the bodies of granite. Narragansett Pier Granite (Permian) - Pink to red, medium- to coarse-grained (commonly pegmatitic), generally massive (not gneissic) granite, composed of microcline, oligoclase, quartz, and biotite, and accessory muscovite and magnetite. Considerable associated pegmatite.

Porphyritic phase [of Potter Hill Granite Gneiss] (Proterozoic Z?)

Porphyritic phase [of Potter Hill Granite Gneiss] - Light- to medium-gray, fine- to medium-grained, porphyritic, well-foliated (not lineated) granitic gneiss, composed of microcline (much of it as megacrysts up to 4 cm long), quartz, oligoclase, biotite and magnetite. Sterling Plutonic Suite is here restricted to the Hope Valley terrane. (The Hope Valley together with the Esmond-Dedham terrane make up the Avalon superterrane of this report.) The Ponaganset Gneiss and the Ten Rod Granite Gneiss lie within the Esmond-Dedham terrane and are therefore removed from the Sterling. The Ponaganset is interpreted as an intensely deformed phase of the Esmond Plutonic Suite. The Sterling, as defined here, includes only the Hope Valley Alaskite Gneiss and the Potter Hill Granite Gneiss. These rocks intrude the Plainfield Formation and the Waterford Group in southeastern CT and western Rhode Island and are Late Proterozoic in age. The gneiss of the Potter Hill is mainly weathered, deeply stained, somewhat crumbly, and generally slabby. Contains xenoliths of the Plainfield Formation. Is distinguished from Hope Valley by its higher biotite content (Skehan and Rast, 1990).

Potter Hill Granite Gneiss (Proterozoic Z?)

Potter Hill Granite Gneiss - Light-pink to gray, tan-weathering, fine- to medium-grained, rarely porphyritic, well-foliated (not lineated) granitic gneiss, composed of microcline, quartz, oligoclase (or albite), biotite, and magnetite, minor muscovite, and local garnet. Sterling Plutonic Suite is here restricted to the Hope Valley terrane. (The Hope Valley together with the Esmond-Dedham terrane make up the Avalon superterrane of this report.) The Ponaganset Gneiss and the Ten Rod Granite Gneiss lie within the Esmond-Dedham terrane and are therefore removed from the Sterling. The Ponaganset is interpreted as an intensely deformed phase of the Esmond Plutonic Suite. The Sterling, as defined here, includes only the Hope Valley Alaskite Gneiss and the Potter Hill Granite Gneiss. These rocks intrude the Plainfield Formation and the Waterford Group in southeastern CT and western Rhode Island and are Late Proterozoic in age. The gneiss of the Potter Hill is mainly weathered, deeply stained, somewhat crumbly, and generally slabby. Contains xenoliths of the Plainfield Formation. Is distinguished from Hope Valley by its higher biotite content (Skehan and Rast, 1990).

Potter Hill Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian)

Potter Hill Granite Gneiss plus Narragansett Pier Granite - Potter Hill Granite Gneiss - Light-pink to gray, tan-weathering, fine- to medium-grained, rarely porphyritic, well-foliated (not lineated) granitic gneiss, composed of microcline, quartz, oligoclase (or albite), biotite, and magnetite, minor muscovite, and local garnet. Narragansett Pier Granite (Permian) - Pink to red, medium- to coarse-grained (commonly pegmatitic), generally massive (not gneissic) granite, composed of microcline, oligoclase, quartz, and biotite, and accessory muscovite and magnetite. Considerable associated pegmatite.

Quartzite unit [in Plainfield Formation] plus Stony Creek Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian)

Quartzite unit [in Plainfield Formation] plus Stony Creek Granite Gneiss plus Narragansett Pier Granite - Quartzite unit [in Plainfield Formation] - light-gray, glassy, generally thin bedded quartzite, also feldspathic and micaceous quartzite containing quartz-sillimanite nodules. Stony Creek Granite Gneiss - Red to pink, unevenly medium to very coarse grained, variably foliated granite or granite gneiss, composed of oligoclase, K-feldspar, and quartz with minor biotite and magnetite, sporatic garnet (in foliated varieties), and local muscovite. Commonly contains granite and pegmatite of Narragansett Pier type (and probably age). In much of area both granites occur as innumerable veins penetrating other units or as larger bodies full of inclusions of those units, which can be mapped through the bodies of granite. Narragansett Pier Granite (Permian) - Pink to red, medium- to coarse-grained (commonly pegmatitic), generally massive (not gneissic) granite, composed of microcline, oligoclase, quartz, and biotite, and accessory muscovite and magnetite. Considerable associated pegmatite.

Scituate Granite Gneiss (Proterozoic Z?)

Scituate Granite Gneiss - Light-pink to gray., medium- to coarse-grained, generally porphyritic, well-lineated and locally foliated granitic gneiss, composed of microcline, quartz, albite or orthoclase, biotite, hornblende, and magnetite. Megacrysts of microcline up to 3 cm long; lineation formed by splotches of biotite or by rods or quartz.

Shelton Member [of Trap Falls Formation] (Middle or Lower Ordovician)

Shelton (white gneiss) Member [of Trap Falls Formation] - White, light-gray, or buff, fine- to medium-grained, generally well foliated granitic gneiss, composed of sodic plagioclase, quartz, microcline, muscovite, and garnet (in tiny almost ubiquitous grains), also commonly minor biotite; generally interlayered with mica schist, biotite gneiss, and calc-silicate rock. Thought to be metavolcanic equivalent of unit Og. Shelton Member of Trap Falls Formation (Rodgers, 1985) is here referred to as Shelton muscovite granite. On the basis of field and laboratory studies, Ansonia, Beardsley, Pumpkin Ground, and Shelton gneisses, previously considered stratigraphic units, are reinterpreted as plutonic. Shelton is a foliated, medium-grained, garnet-bearing muscovite leucogranite with a conspicuous white color and abundant garnets. Age of crystallization determined from U-Pb garnet analysis is 380+/-3 Ma (Middle Devonian). Southeast margin of the Shelton is in contact with the Trap Falls Formation (Sevigny and Hanson, 1993).

Stony Creek Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian)

Stony Creek Granite Gneiss plus Narragansett Pier Granite - Stony Creek Granite Gneiss - Red to pink, unevenly medium to very coarse grained, variably foliated granite or granite gneiss, composed of oligoclase, K-feldspar, and quartz with minor biotite and magnetite, sporatic garnet (in foliated varieties), and local muscovite. Commonly contains granite and pegmatite of Narragansett Pier type (and probably age). In much of area both granites occur as innumerable veins penetrating other units or as larger bodies full of inclusions of those units, which can be mapped through the bodies of granite. Narragansett Pier Granite (Permian) - Pink to red, medium- to coarse-grained (commonly pegmatitic), generally massive (not gneissic) granite, composed of microcline, oligoclase, quartz, and biotite, and accessory muscovite and magnetite. Considerable associated pegmatite.

Trap Falls Formation plus Ordovician? granitic gneiss (Middle or Lower Ordovician)

Trap Falls Formation plus Ordovician? granitic gneiss - 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. Ordovician? granitic gneiss (including local terms Ansonia, Mine Hill, "Tyler Lake," "Siscowit") - White, light-gray, buff, or pink, generally foliated granitic gneiss, composed of sodic plagioclase, quartz, microcline, muscovite, and biotite, and locally garnet or sillimanite. Commonly contains numerous inclusions or layers of mica schist and gneiss.

Waterford Group and Branford Gneiss (Proterozoic Z?)

Waterford Group (may be equivalent in part to Monson Gneiss) - Interlayered part (but layers locally distinct) of Waterford Group, light to dark, generally medium grained gneiss, composed of plagioclase, quartz, and biotite, with hornblende in some layers and microcline in others. Some layers of amphibolite. Branford Gneiss - Gray to white but rarely pink., medium-grained, well-foliated granitic gneiss, composed of oligoclase, K-feldspar, quartz, biotite, garnet, magnetite, and muscovite.

Waterford Group plus Stony Creek Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian)

Waterford Group plus Stony Creek Granite Gneiss plus Narragansett Pier Granite - Waterford Group (may be equivalent in part to Monson Gneiss) - Interlayered part (but layers locally distinct) of Waterford Group, light to dark, generally medium grained gneiss, composed of plagioclase, quartz, and biotite, with hornblende in some layers and microcline in others. Some layers of amphibolite. Stony Creek Granite Gneiss - Red to pink, unevenly medium to very coarse grained, variably foliated granite or granite gneiss, composed of oligoclase, K-feldspar, and quartz with minor biotite and magnetite, sporatic garnet (in foliated varieties), and local muscovite. Commonly contains granite and pegmatite of Narragansett Pier type (and probably age). In much of area both granites occur as innumerable veins penetrating other units or as larger bodies full of inclusions of those units, which can be mapped through the bodies of granite. Narragansett Pier Granite (Permian) - Pink to red, medium- to coarse-grained (commonly pegmatitic), generally massive (not gneissic) granite, composed of microcline, oligoclase, quartz, and biotite, and accessory muscovite and magnetite. Considerable associated pegmatite.

Georgia

Amphibolite/ Epidote Quartzite/ Granite Gneiss (Precambrian-Paleozoic)

Amphibolite/ Epidote Quartzite/ Granite Gneiss

Biotite Gneiss/ Hornblende Gneiss/ Granite Gneiss (Age not given)

Biotite Gneiss/ Hornblende Gneiss/ Granite Gneiss

Biotite Granite Gneiss/ Feldspathic Biotite Gneiss/ Amphibolite Hornblende Gneiss (Precambrian-Paleozoic)

Biotite Granite Gneiss/ Feldspathic Biotite Gneiss/ Amphibolite Hornblende Gneiss

Calc-silicate Granite Gneiss (Precambrian-Paleozoic)

Calc-silicate Granite Gneiss

Granite Gneiss/ Amphibolite (Precambrian-Paleozoic)

Granite Gneiss/ Amphibolite

Granite Gneiss/ Granite (Precambrian-Paleozoic)

Granite Gneiss/ Granite

Granite/ granite gneiss (Precambrian-Paleozoic)

Granite/ granite gneiss

Granitic Gneiss / Gneissic Granite (augen or porphyritic) (Precambrian-Paleozoic)

Granitic Gneiss / Gneissic Granite (augen or porphyritic)

Granitic Gneiss undifferentiated (Precambrian-Paleozoic)

Granitic Gneiss undifferentiated

Hornblende Gneiss/ Amphibolite/ Granite Gneiss (Precambrian-Paleozoic)

Hornblende Gneiss/ Amphibolite/ Granite Gneiss

Hornblende Gneiss/ Granite Gneiss/ Biotite Gneiss (Precambrian-Paleozoic)

Hornblende Gneiss/ Granite Gneiss/ Biotite Gneiss

Muscovite Granite Gneiss (Precambrian-Paleozoic)

Muscovite Granite Gneiss

Quartzite/ Biotite Granite Gneiss (Precambrian-Paleozoic)

Quartzite/ Biotite Granite Gneiss

Sericite Schist/ Amphibolite/ Granite gneiss (Precambrian-Paleozoic)

Sericite Schist/ Amphibolite/ Granite gneiss

Massachusetts

Belchertown Complex (Devonian)

Belchertown Complex (intrudes De) - Outer zone of hornblende quartz monzodiorite gneiss.

Biotite granitic gneiss (Devonian)

Biotite granitic gneiss.

Coys Hill Porphyritic Granite Gneiss (Lower Devonian)

Coys Hill Porphyritic Granite Gneiss - Coarse-grained porphyritic microcline granite gneiss, commonly containing garnet and sillimanite with or without muscovite; continuous with the Cardigan and Ashuelot plutons of Kinsman Quartz Monzonite in New Hampshire; appears to be an early quasi-concordant intrusion within Dl.

Dry Hill Gneiss (Proterozoic Z)

Dry Hill Gneiss - Pink microcline-biotite and microcline-hornblende gneiss containing pink microcline megacrysts and minor quartzite.

Fish Brook Gneiss (Ordovician or Proterozoic Z)

Fish Brook Gneiss - Light-gray, biotite-plagioclase quartz gneiss; distinctive "swirl-form" foliation.

Fitchburg Complex (Lower Devonian or younger)

Fitchburg Complex - Light-gray, strongly foliated biotite-muscovite granite to granodiorite gneiss; common small to very large inclusions of Dl, some mapped separately.

Fitchburg Complex (Lower Devonian or younger)

Fitchburg Complex - Dfgd containing many zones of foliated biotite-muscovite granite gneiss and inclusions of mica schist and feldspathic granulite.

Fitchburg Complex (Lower Devonian or younger)

Fitchburg Complex -Dark-gray, strongly foliated biotite granodiorite to tonalite gneiss; resembles Dht; intrudes and contains inclusions of Dl, some mappable; locally cut by sills identical to Dfgrg.

Glastonbury Gneiss (Ordovician)

Glastonbury Gneiss - Massive granitic gneiss in core of Glastonbury dome and in adjacent areas.

Gneiss at Hallockville Pond (Ordovician)

Gneiss at Hallockville Pond - Light-gray foliated microcline-plagioclase-quartz biotite gneiss containing microcline megacrysts. Intrudes Om.

Granitoid Gneiss (Proterozoic Y)

Granitoid gneiss - Biotite ferrohastingsite granodioritic and granitic gneiss with large schlieren of biotite, locally contains garnet and muscovite.

Gray, well-layered biotite-plagioclase-quartz gneiss (Proterozoic Y)

Gray, well-layered biotite-plagioclase-quartz gneiss - Ybu may contain undifferentiated areas of Ycs, Yl, and Yhb.

Gray, well-layered biotite-plagioclase-quartz gneiss (Proterozoic Y)

Gray, well-layered biotite-plagioclase-quartz gneiss - Containing beds of amphibolite, aluminous schist, quartzite, and calc-silicate gneiss.

Hardwick Tonalite (Lower Devonian)

Hardwick Tonalite - Dark-gray, moderately to strongly foliated biotite tonalite to granodiorite gneiss; intrudes Dl.

Hardwick Tonalite (Lower Devonian)

Hardwick Tonalite - Porphyritic microcline-biotite granite gneiss in sills intruding Dht.

Marlboro Formation (Ordovician, Cambrian, or Proterozoic Z)

Marlboro Formation - Homogeneous light-gray feldspathic gneiss.

Pauchaug Gneiss (Ordovician)

Glastonbury Gneiss - Massive granitic gneiss in cores of Warwick and Vernon domes.

Stamford Granite Gneiss (Proterozoic Y)

Stamford Granite Gneiss - White to gray biotite-oligoclase-microcline Rapakivi granite gneiss containing blue quartz. Intrudes Yb, Ybu.

Tyringham Gneiss (Proterozoic Y)

Tyringham Gneiss - Light pinkish-gray ferrohastingsite-biotite, quartz-rodded granodioritic to quartz monzonitic gneiss, coarsely porphyritic, locally having fine-grained aplitic border. Intrudes all Berkshire Proterozoic Y units.

Maryland

Baltimore Gneiss (Precambrian)

Baltimore Gneiss - Biotite-quartz-feldspar gneiss and biotite-hornblende gneiss; amphibolite widespread but subordinate; texturally varied; granitic gneiss, veined gneiss, augen gneiss, banded gneiss, and migmatite, in places complexly intermingled; age 1,1000 m.y. * by radiogenic dating. Layered paragneiss in Baltimore City southeast of Relay Quartz Diorite.

Granodiorite and Biotite Granite Gneiss (Precambrian)

Granodiorite and Biotite Granite Gneiss - Light gray to pale green, fine-grained, granodiorite gneiss, and dark gray biotite granite gneiss with some augen gneiss; in places a sheared muscovite-biotite gneiss; local biotite schist bands; intruded by metadiabase feeder dikes of Catoctin Metabasalt.

James Run Gneiss (Late Precambrian (?))

James Run Gneiss - Thick-bedded, light gray biotite-quartz-plagioclase gneiss with thin interbeds of quartz amphibolite; grades downward into sharply layered, thin- to thick-bedded paragneiss composed of subequal amounts of biotite-quartz-plagioclase gneiss and quartz amphibolite; thickness unknown.

Muscovite Quartz Monzonite Gneiss (Paleozoic)

Muscovite Quartz Monzonite Gneiss - Well foliated to nearly massive quartz monzonite gneiss, generally medium-grained and even textured but locally porphyritic and pegmatitic.

Port Deposit Gneiss (Paleozoic)

Port Deposit Gneiss - Moderately to strongly deformed intrusive complex composed of gneissic biotite quartz diorite, hornblende-biotite quartz diorite, and biotite granodiorite; all rocks foliated and some strongly sheared; age 550 +/- 50 m.y. * by radiogenic dating.

North Carolina

Biotite Granitic Gneiss (Middle Proterozoic)

Biotite Granitic Gneiss - unconformity; pinkish gray to light gray, massive to well-foliated, granitic to quartz monzonitic; includes variably mylonitized orthogneiss and paragneiss, interlayered amphibolite, calc-silicate rock, and marble. Includes granites of the Bryson City area, Straight Fork window, and Elk Park Plutonic Suite.

Biotite Granitic Gneiss (Middle Proterozoic)

Biotite Granitic Gneiss (950-1250 my) - unconformity; contains paragneiss and granitic to quartz monzonitic orthogneiss; locally schistose and mylonitic. Locally includes tectonic slices, infolded remnants, or recrystallized equivalents of the Grandfather Mountain Formation. Equivalent to the Wilson Creek Gneiss.

Caesars Head Granite Gneiss (Devonian/Silurian)

Caesars Head Granite Gneiss (409 my) - equigranular to porphyritic, massive to well foliated; contains biotite and muscovite.

Granite Gneiss (Silurian/Ordovician)

Granite Gneiss (438 my) - poorly foliated; interlayered with biotite augen gneiss.

Granitic Gneiss (Late Middle Proterozoic)

Granitic Gneiss (1192 my) - megacrystic, in places contains amphibolite.

Granodioritic Gneiss (Middle Proterozoic)

Granodioritic Gneiss (1175 my) - unconformity; greenish gray to pinkish gray, porphyroclastic to mylonitic; epidote, sericite, and chlorite common.

Migmatitic Granitic Gneiss (Ordovician/Cambrian)

Migmatitic Granitic Gneiss - foliated to massive, granitic to quartz dioritic; biotite gneiss and amphibolite common.

Rabun Gneiss (Ordovician)

Rabun Gneiss (450-500 my) - weakly to well foliated, granitic to quartz monzonitic.

Shelton Granite Gneiss (Silurian)

Shelton Granite Gneiss (429 my) - poorly foliated; lineated granitic to quartz monzonitic gneiss.

Toxaway Gneiss (Middle Proterozoic)

Toxaway Gneiss (1203 my) - unconformity; poorly foliated to well-foliated; equigranular to inequigranular, granitic.

New Hampshire

Rye Complex, Breakfast Hill Granite of Novotny (1964). (Ordovician? - Late Proterozoic? )

Breakfast Hill Granite of Novotny (1964) - Blastomylonitic quartz-feldspar granitic gneiss and pegmatite intruded the Rye Complex and formed a migmatite.

New York

Biotite and/or hornblende granite gneiss (Middle Proterozoic)

Biotite and/or hornblende granite gneiss - locally pyroxenic; commonly with subordinate leucogranitic gneiss, biotite-quartz-plagioclase gneiss, other metasedimentary rocks, amphibolite, migmatite. Amphibolite with porphyroblasts of K-feldspar locally prominent in northwest Adirondacks. In northwest Adirondacks, grades into Yphg.

Biotite and/or hornblende granite gneiss (Middle Proterozoic)

Biotite and/or hornblende granite gneiss - locally pyroxenic; commonly with subordinate leucogranitic gneiss, biotite-quartz-plagioclase gneiss, other metasedimentary rocks, amphibolite, migmatite. Amphibolite with porphyroblasts of K-feldspar locally prominent in northwest Adirondacks. Overprint signifies inequigranular texture or phacoidal structure. In northwest Adirondacks, grades into Yphg.

Biotite and/or hornblende granite gneiss (Middle Proterozoic)

Biotite and/or hornblende granite gneiss - locally pyroxenic; commonly with subordinate leucogranitic gneiss, biotite-quartz-plagioclase gneiss, other metasedimentary rocks, amphibolite, migmatite. Amphibolite with porphyroblasts of K-feldspar locally prominent in northwest Adirondacks. Overprint signifies inequigranular texture or phacoidal structure. In northwest Adirondacks, grades into Yphg.

Biotite granite gneiss (Middle Proterozoic)

Biotite granite gneiss - overprint signifies inequigranular texture.

Biotite granite gneiss (Middle Proterozoic)

Biotite granite gneiss - overprint signifies inequigranular texture.

Biotite-hornblende granite and granite gneiss (Middle Proterozoic)

Biotite-hornblende granite and granite gneiss.

Biotite-quartz-plagioclase gneiss (Middle Proterozoic)

Biotite-quartz-plagioclase gneiss - with subordinate biotite granitic gneiss, amphibolite, calcsilicate rock.

Charnockite, granitic and quartz syenite gneiss (Middle Proterozoic)

Charnockite, granitic and quartz syenite gneiss - variably leucocratic, containing varying amounts of hornblende, pyroxenes, biotite; may contain interlayered amphibolite, metasedimentary gneiss, migmatite. Overprint signifies inequigranular texture or phacoidal structure.

Charnockite, granitic and quartz syenite gneiss (Middle Proterozoic)

Charnockite, granitic and quartz syenite gneiss - variably leucocratic, containing varying amounts of hornblende, pyroxenes, biotite; may contain interlayered amphibolite, metasedimentary gneiss, migmatite. Overprint signifies inequigranular texture or phacoidal structure.

Ferrohedenbergite-fayalite granite and granite gneiss (Middle Proterozoic)

Ferrohedenbergite-fayalite granite and granite gneiss.

Hornblende granite and granite gneiss (Middle Proterozoic)

Hornblende granite and granite gneiss - with subordinate leucogranite.

Interlayered amphibolite and hornblende granitic gneiss (Middle Proterozoic)

Interlayered amphibolite and hornblende granitic gneiss.

Interlayered metasedimentary rock and granitic gneiss (Middle Proterozoic)

Interlayered metasedimentary rock and granitic gneiss.

Leucogranitic (alaskitic) gneiss (Middle Proterozoic)

Leucogranitic (alaskitic) gneiss - sodic plagioclase ranges from generally subordinate to locally dominant; locally with biotite, hornblende, pyroxene, garnet, sillimanite, disseminated magnetite; commonly contains metasedimentary layers, amphibolite, migmatite; plagioclase-rich variety is host to magnetite ore bodies in eastern Adirondacks.

Leucogranitic gneiss (Middle Proterozoic)

Leucogranitic gneiss

Leucogranitic gneiss (Middle Proterozoic)

Leucogranitic gneiss - sodic plagioclase ranges from generally subordinate to locally dominant; locally with biotite, hornblende, pyroxene, garnet, sillimanite, disseminated magnetite; commonly contains metasedimentary layers, amphibolite, migmatite; plagioclase-rich variety is host to magnetite ore bodies in eastern Adirondacks.

Muscovite-biotite granite gneiss (Upper Devonian)

Muscovite-biotite granite gneiss

Pyroxene and/or hornblende granitic gneiss (Middle Proterozoic)

Pyroxene and/or hornblende granitic gneiss - biotitic in part; sodic plagioclase ranges from generally subordinate to locally dominant; plagioclase-rich facies locally contain disseminated magnetite and magnetite ore bodies; grades westward into Yhbg, and southward into Ylg.

Pennsylvania

Granitic gneiss and granite (Probably lower Paleozoic)

Granitic gneiss and granite - Includes Springfield Granodiorite (granitized Wissahickon) in Philadelphia area.

Rhode Island

Esmond Igneous Suite - granite gneiss (Late Proterozoic)

Esmond Igneous Suite - granite gneiss - Pale-gray to pale-pink, fine- to medium-grained granite gneiss, rarely with porphyroclasts of microcline/orthoclase. Composition ranges from quartz monzonite to granite. Composed of sodic plagioclase, quartz, microcline, biotite, opaque minerals; minor muscovite common, garnet more rare; accessory apatite and zircon; sphene and hornblende present in some rocks; secondary chlorite. Typically massive, but with strong penetrative foliation and lineation defined by major minerals. Commonly associated with, and in part gradational into, augen gneiss. Includes rock mapped formerly in part as Ponaganset Granite Gneiss, Scituate Granite Gneiss, Ten Rod Granite Gneiss, and Hope Valley Alaskite Gneiss.

Harmony Group - Absalona Formation (Late Proterozoic? or older?)

Harmony Group - Absalona Formation - Gray, medium- to coarse-grained biotite granite gneiss characterized by alkali feldspar porphyroblasts. Consists of biotite, hornblende, quartz, microcline, microperthite, albite, epidote, garnet, and chlorite. Subordinate amounts of quartz-biotite schist, amphibolite, and quartzite occur as layers and isolated bodies.

Harmony Group - Nipsachuck Formation (Late Proterozoic? or older?)

Harmony Group - Nipsachuck Formation - Gray to tan, fine- to medium-grained granite gneiss, characterized by biotite streaks. Consists of biotite, muscovite, quartz, microperthite, and sodic plagioclase.

Sterling Igneous Suite - alaskite gneiss (Late Proterozoic)

Sterling Igneous Suite - alaskite gneiss - Pale pink, orange, or gray, fine- to medium-grained granite gneiss, rarely with porphyroclasts of microcline/orthoclase. Composition is granite with generally less than 3% dark minerals. Composed of sodic plagioclase, quartz, microcline/orthoclase, minor biotite, and opaque minerals; minor muscovite (in part secondary), and rare garnet and sphene in some rocks; accessory apatite and zircon; secondary chlorite. Varies from massive to layered. Strongly foliated and locally well lineated. Includes most rock mapped formerly as Hope Valley Alaskite Gneiss.

Sterling Igneous Suite - granite gneiss (Late Proterozoic)

Sterling Igneous Suite - granite gneiss - Pale pink to gray, medium-grained granite gneiss, commonly with small porphyroclasts of microcline/orthoclase. Similar to alaskite gneiss, but with more than 3% dark minerals. Composition is granite with generally less than 3% dark minerals. Compositions range from quartz monzonite to granite. Composed of sodic plagioclase, quartz, microcline, biotite, opaque minerals; minor muscovite common, garnet more rare; accessory apatite and zircon; sphene present in some rocks; secondary chlorite. Typically is compositionally homogeneous, with strong foliation and locally well-developed lineation defined by major minerals. Includes some rock mapped formerly as Ten Rod Granite Gneiss, Hope Valley Alaskite Gneiss, Potter Hill Granite Gneiss, and Scituate Granite Gneiss.

Waterford Group - Rope Ferry Gneiss (Late Proterozoic? or older?)

Waterford Group - Rope Ferry Gneiss - Light- to dark gray, fine- to medium-grained tonalite gneiss composed of plagioclase, quartz biotite, and hornblende, commonly interlayered with granite gneiss composed of microcline, plagioclase, quartz, biotite, and hornblende; local layers of amphibolite.

South Carolina

Caesars Head Granite (Ordovician to Silurian)

Caesars Head Granite: well foliated, banded to non-banded biotite granitoid gneiss or gneissic granitoid; cuts Seneca thrust fault

Gneissic granite of Antreville pluton (Silurian to Ordovician)

Gneissic granite of Antreville pluton: gneissic biotite granite to granodiorite

Gneissic granite of Greenville (Paleozoic)

Gneissic granite of Greenville: granite gneiss

Gneissic granite of Starr (Silurian to Ordovician)

Gneissic granite of Starr: gneissic biotite granite to granodiorite of Starr pluton and nearby satellite plutons

Granite gneiss (Silurian to Ordovician)

Granite gneiss: equigranular to inequigranular granite gneiss and augen gneiss, undivided

Granite sheets near Joanna (Paleozoic)

Granite sheets near Joanna

Granodiorite gneiss and granite gneiss (Devonian to Silurian)

Granodiorite gneiss and granite gneiss

Migmatitic granitoid gneiss (Ordovician)

Migmatitic granitoid gneiss: variably foliated, variably migmatitic, and granitic to quartz dioritic in composition

Reedy River complex (Paleozoic)

Reedy River complex: gneissic biotite granite to granodiorite

Toluca Granite and associated metagranites (Ordovician)

Toluca Granite and associated metagranites: weakly to strongly foliated, garnet-bearing, metamorphosed monzogranite to granodiorite; ranges from equigranular and medium-grained to inequigranular having coarse microcline megacrysts

Toxaway Gneiss (Mesoproterozoic)

Toxaway Gneiss: banded granite gneiss consisting of very light gray layers rich in quartz, plagioclase, and microcline alternating with dark gray biotite-rich layers

Virginia

Bassett Formation - Biotite gneiss and granite gneiss. (Proterozoic Z)

Bassett Formation - Quartzofeldspathic biotite gneiss and granite gneiss.

Biotite Granite Gneiss (Proterozoic Y)

Biotite granite gneiss

Biotite Granite Gneiss (Proterozoic)

Biotite granite gneiss

Biotite-Muscovite Leucogranite Gneiss (Proterozoic Y)

Biotite-muscovite leucogranite gneiss

Charnockite (Proterozoic Y)

Charnockite.

Goldvein Pluton (Cambrian-Ordovician)

Goldvein Pluton - Metamonzogranite.

Granite Gneiss (Proterozoic Y-Pennsylvanian)

Granite gneiss.

Layered Leucocratic Granite Gneiss (Proterozoic Y)

Layered leucocratic granite gneiss

Lineated Biotite Granite Gneiss (Proterozoic)

Lineated biotite granite gneiss

Porphyroblastic Granite Gneiss (Proterozoic Y)

Porphyroblastic granite gneiss

Vermont

Bethlehem Gneiss (Devonian)

Bethlehem Gneiss - Two-mica granodiorite gneiss. Revised as the Bethlehem Granodiorite to emphasize its average granodiorite composition. Mapped as the Haverhill, Mount Clough, Indian Pond, and Fairlee plutons. Consists of strongly metamorphosed, foliated, gray, medium-grained biotite granodiorite and local tonalite and granite. Age is Devonian based on isotopic age of 410+/-5 Ma (J.N. Aleinikoff, this report, from Fairlee pluton), which is also consistent with age of 409+/-5 Ma reported by Kohn and others (1992) from Indian Pond pluton and Bellows Falls pluton (the latter is outside of map area in southwestern NH) (Moench and others, 1995).

Biotite Quartz Diorite Gneiss (Devonian)

Biotite quartz diorite gneiss.

Undifferentiated Gneiss (Precambrian)

Undifferentiated Gneiss - Undifferentiated gneissic biotite granite, quartz monzonite, and granodiorite.

Undifferentiated Granitic Gneiss (Devonian)

Undifferentiated Granitic Gneiss - Small dikes and sills do not show.

Wisconsin

Granite gneiss (Early Proterozoic)

Granite gneiss - Medium-grained granodiorite gneiss in northwestern Marathon County.

Wyoming

Granite gneiss (Archean)

GRANITE GNEISS (AGE 2,600 TO 3,100+ Ma)--Layered to massive, locally migmatitic; metasedimentary and metavolcanic rocks locally common. Includes Webb Canyon Gneiss in Teton Range.

Oldest gneiss complex (Archean)

OLDEST GNEISS COMPLEX--Chiefly layered granitic gneiss, locally migmatitic. Local masses of quartzite, metagraywacke, iron-formation, and other metasedimentary rocks and amphibolite and felsic gneiss thought to be volcanic; metasedimentary rocks in Beartooth Mountains contain detrital zircon dated at more than 3,400 Ma. Inclusions show evidence of granulite-facies metamorphism prior to 2,800 Ma. Mueller and others (1982) suggest that large areas in Beartooth Mountains were invaded by Late Archean granite (age about 2,800 Ma). Bighorn Mountains--Dates of metamorphism 3,000+ Ma.

Oldest gneiss complex (Archean)

OLDEST GNEISS COMPLEX--Chiefly layered granitic gneiss, locally migmatitic. Local masses of quartzite, metagraywacke, iron-formation, and other metasedimentary rocks and amphibolite and felsic gneiss thought to be volcanic; metasedimentary rocks in Beartooth Mountains contain detrital zircon dated at more than 3,400 Ma. Inclusions show evidence of granulite-facies metamorphism prior to 2,800 Ma. Mueller and others (1982) suggest that large areas in Beartooth Mountains were invaded by Late Archean granite (age about 2,800 Ma). Wind River Range--Includes large bodies of metagabbro. Overprint pattern indicates area of migmatite related to emplacement of 2,600-Ma granite.