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Geologic units containing alkali-granite (alaskite)

Earth material > Plutonic rock > Granitoid
Alkali-feldspar granite
A plutonic rock defined in the QAPF diagram as having Q between 20 and 60% and P/(A+P) < 10%
This category is also used for alkali-granite (alaskite).
Subtopics:
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California - Idaho - Massachusetts - Maine - Nevada - Rhode Island - Virginia
California
Mesozoic granitic rocks, unit 1 (Salinian Block) (Early to Late Cretaceous)
Mesozoic granite, quartz monzonite, granodiorite, and quartz diorite
Mesozoic granitic rocks, unit 3 (Sierra Nevada, Death Valley area, Northern Mojave Desert and Transverse Ranges) (Permian to Tertiary; most Mesozoic)
Mesozoic granite, quartz monzonite, granodiorite, and quartz diorite
Idaho
Alaskite, hornfels, and quartzite, undivided; Mixed Tertiary to Cretaceous intrusions and Middle Proterozoic host rocks, undivided; central Idaho (Eocene and Middle Proterozoic, mixed)
Mixed, highly altered and migmatitic rocks; derived from imbrication and dynamic events.
Diorite, gabbro, and granite; Jurassic to Triassic plutons; western Idaho, Blue Mountains island-arc complex (Jurassic to Triassic)
Lower Mesozoic intrusions; localized near the Snake Canyon of western Idaho.
Granodiorite, quartz monzonite, granite, alaskite, quartz monzodioirte, diorite; Tertiary to Cretaceous, intrusions, undivided; northern, west-central, and southwestern Idaho (Eocene to Cretaceous)
Eocene intrusions; Cretaceous plutons, intermediate, Cretaceous plutons, felsic; metamorphosed granitic intrusive rock
Intrusive rocks: mostly Late Cretaceous granodioritic to granitic plutons of the Idaho batholithic assemblage, but including some Eocene intrusions; northern Idaho and Atlanta batholith (Cretaceous to Eocene)
Cretaceous plutons; probably includes unmapped older and younger crystalline bodies.
Massachusetts
Alaskite (Proterozoic Z)
Alaskite - Light-gray, pinkish-gray to tan, mafic-poor granite commonly containing muscovite.
Alkalic granite in Franklin (Devonian to Ordovician)
Alkalic granite in Franklin .
Cape Ann Complex (Lower Silurian or Upper Ordovician)
Cape Ann Complex - Alkalic granite to quartz syenite containing ferro-hornblende. Intrudes Zdigb. Most of Cape Ann Complex forms Cape Ann peninsula of northeastern MA. Consists of alkalic granite to quartz syenite (its main phase), Beverly Syenite, and Squam Granite, all of which form a pluton covering 385 sq km. Intrudes Late Proterozoic greenschist, diorite, and gabbro that earlier workers assigned to Marlboro Formation, Salem Gabbro-Diorite, or Middlesex Fells Volcanic Complex. Dennen (1975) considered masses of diorite and gabbro within and adjacent to Cape Ann Complex to be cogenetic with it and equivalent in age to Nahant Gabbro and gabbro at Salem Neck. Authors recommend that usage of term Salem Gabbro-Diorite be restricted to these masses of diorite and gabbro in and around Cape Ann pluton that are younger than Dedham Granite and cogenetic with Cape Ann Complex. Gabbro at Salem Neck is probably representative. Radiometric ages straddle Late Ordovician-Early Silurian boundary. Age is based on Rb-Sr whole rock isochron of 426 +/-6 Ma (Zartman and Marvin, 1971) and U-Pb zircon date of 450 +/-25 Ma (Zartman, 1977) (Wones and Goldsmith, 1991).
Cherry Hill Granite (Devonian)
Cherry Hill Granite - Alaskite granite containing ferro-hornblende. Intrudes Dwn.
Hope Valley Alaskite Gneiss (Proterozoic Z)
Hope Valley Alaskite Gneiss - Mafic-poor gneissic granite, locally muscovitic. Gradational with Zsg. Late Proterozoic Hope Valley Alaskite Gneiss occurs as one of several plutonic rocks in Milford antiform. Forms tabular masses along west side of Rhode Island anticlinorium from southern RI and eastern CT to northwestern RI; flanks west side of Milford anticlinorium and terminates at north end of anticlinorium in MA. Color is light pink to tan. Intrudes Plainfield Formation in CT and Blackstone Group rocks in RI. Isotopic age of 630 Ma by U/Pb methods on zircon is reported by Zartman and Naylor (1984) from a sample in MA. Age of 601 +/-5 Ma by U/Pb methods on zircon is reported by Hermes and Zartman (1985) from a sample in RI (Wones and Goldsmith, 1991).
Peabody Granite (Middle Devonian)
Peabody Granite - Alkalic granite containing ferro-hornblende. Intrudes Zgb, Zdngr.
Quincy Granite (Lower Silurian or Upper Ordovician)
Quincy Granite - Alkalic granite containing riebeckite and aegirine. Intrudes CAbw and PZZc (?). Quincy Granite intrudes Middle Cambrian Braintree Argillite. Southern contact is with chemically and mineralogically similar Blue Hills Granite Porphyry. Fresh rock is dark gray to dark green, weathering to buff brown or salmon. Bounded on the northwest by Blue Hills thrust and on the west by Neponset fault. No clasts of Quincy observed in Early Pennsylvanian Pondville Conglomerate, but clasts of overlying and probably related Blue Hills Granite Porphyry are common in Pondville. Combined area of Quincy and Blue Hills rocks is 55 sq km. Small mass of "Quincy Granite" east of Woonsocket, RI, near RI-MA border is similar in texture to Quincy Granite at Quincy, MA, but is more peralkaline. The mass near Woonsocket was thought at the time of compilation of the MA State geologic map (Zen and others, 1983) to be same general age as granite at Quincy. Age of mass at Woonsocket has been more recently determined to be Devonian or possibly Carboniferous, rather than Late Ordovician and Silurian (Hermes and Zartman (1985) (Wones and Goldsmith, 1991).
White, magnetite-bearing alaskite and trondhjemite (Ordovician)
White, magnetite-bearing alaskite and trondhjemite - Associated with blastomylonite along thrust slices. Intrudes Proterozoic Y gneisses.
Maine
Cretaceous alkali feldspar granite (Cretaceous)
Cretaceous alkali feldspar granite - Cretaceous alkali feldspar-biotite granite
Nevada
Intrusive rocks (Late Cretaceous to Middle Miocene)
INTRUSIVE ROCKS-Aphanitic, porphyritic, and coarsely granular rocks ranging in composition from diorite to granite. Clark County
Rhode Island
alkali-feldspar granite of Cumberland (Devonian? or Mississippian?)
alkali-feldspar granite of Cumberland - Gray to blue-gray. medium- to coarse-grained, equigranular to porphyritic alkali-feldspar granite (phenocrysts of perthite). Massive to locally foliated. Contains perthite, quartz, abundant accessory riebeckite and aegerine, and lesser astrophyllite, anegmatite, zircon, allanite, fluorite, and opaque minerals. Plagioclase is notably absent. Hypersolvus, strongly peralkaline granite. Includes rock mapped formerly as Rhode Island Quincy Granite.
Scituate Igneous Suite - alkali-feldspar granite (Devonian)
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.
Virginia
Alaskite (Proterozoic)
Alaskite

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