Geologic units in Ashe county, North Carolina

Additional scientific data in this geographic area

Biotite Granitic Gneiss (Middle Proterozoic) at surface, covers 35 % of this area

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.

Ashe Metamorphic Suite and Tallulah Falls Formation; Muscovite-biotite gneiss (Late Proterozoic) at surface, covers 24 % of this area

Locally sulfidic; interlayered and gradational with mica schist, minor amphibolite, and hornblende gneiss.

Ashe Metamorphic Suite and Tallulah Falls Formation; Amphibolite (Late Proterozoic) at surface, covers 21 % of this area

Equigranular, massive to well foliated, interlayered, rarely discordant, metamorphosed intrusive to extrusive mafic rock; may include metasedimentary rock.

Alligator Back Formation; Gneiss (Late Proterozoic) at surface, covers 10 % of this area

Finely laminated to thin layered; locally contains massive gneiss and micaceous granule conglomerate; includes schist, phyllite, and amphibolite.

Mount Rogers Formation; Metagraywacke (Late Proterozoic) at surface, covers 3 % of this area

Interlayered with metaconglomerate, laminated metasiltstone, and slate; minor calcareous metasandstone, greenstone, and metarhyolite.

Mount Rogers Formation; Metafelsite (Late Proterozoic) at surface, covers 2 % of this area

Light-colored porphyritic extrusive rock.

Meta-ultramafic Rock (Paleozoic/Late Proterozoic) at surface, covers 2 % of this area

Metamorphosed dunite, local peridotite; serpentinite, soapstone, and other altered ultramafic rock. Only larger bodies shown.

Ashe Metamorphic Suite and Tallulah Falls Formation; Mica schist (Late Proterozoic) at surface, covers 0.9 % of this area

Locally sulfidic and graphitic; minor interlayered mica gneiss and amphibolite.

Metamorphosed Granitic Rock (Late Proterozoic) at surface, covers 0.6 % of this area

Massive to foliated, locally mylonitic. Beech, Crossnore, Brown Mountain, Lansing, and other granitic rocks.

Alligator Back Formation; Amphibolite (Late Proterozoic) at surface, covers 0.6 % of this area

Equigranular, massive to well foliated, interlayered, rarely discordant, metamorphosed intrusive and extrusive mafic rock; may include metasedimentary rock.

Chilhowee Group; Lower Chilhowee (Cambrian) at surface, covers 0.4 % of this area

Feldspathic arenite, white to yellowish gray. Minor silty shale, feldspathic siltstone, and conglomerate in lower part. Includes Unicoi Formation of Hot Springs window.

Mount Rogers Formation - Conglomerate, graywacke, laminated siltstone, and shale. (Proterozoic Z) at surface, covers 0.1 % of this area

Graywacke conglomerate, graywacke, tuffaceous sandstone, laminated siltstone, shale, and minor greenstone and rhyolite. Most of the sedimentary rocks are volcanigenic but contain a significant detrital contribution from the underlying crystalline rocks of the Grenville-age basement.

Cranberry Granite (Precambrian) at surface, covers 0.1 % of this area

Complex of intertonguing rock types including migmatite, granitic gneisses, monzonite, quartz diorite, greenstone, mica and hornblende schists, abundant granitic pegmatite.

Alligator Back Formation; Mica schist and phyllite (Late Proterozoic) at surface, covers < 0.1 % of this area

Laminated to thin layered; interlayered with minor biotite-muscovite gneiss and amphibolite.

Mount Rogers Formation - Porphyritic felsite (Proterozoic Z) at surface, covers < 0.1 % of this area

Includes coarsely porphyritic felsite from the Pond Mountain volcanic center that could be a hypabys sal intrusive, and porphyritic rhyolite from the Razor Ridge volcanic center that is extrusive, as well as the Fees Rhyolite Member near the base of the formation.

Elk Park Plutonic Group - Biotite quartz monzonite (Proterozoic Y) at surface, covers < 0.1 % of this area

Elk Park Plutonic Group (Yep, Yec; Rankin and others, 1972; 1973) Includes augen gneiss and porphyritic gneiss (Yep), and equigranular quartz monzonite, quartz monzonite flaser gneiss, and quartz monzonite gneiss (Yec). Rocks range in composition from diorite to quartz monzonite; most are quartz monzonite in which the primary dark mineral is biotite, with or without hornblende; epidote and titanite are common accessory minerals. Porphyritic rocks contain microcline phenocrysts. Augen gneiss was probably derived from porphyritic plutonic rocks by shearing. This unit includes in part the Little River Gneiss of Dietrich (1959) and Cranberry Gneiss (Rankin and others, 1972; 1973). U-Pb zircon data from the Cranberry has been interpreted to signify ages of 1050 Ma (Davis and others, 1962) and 1080 Ma (Rankin and others, 1969).

Unicoi Formation (Cambrian) at surface, covers < 0.1 % of this area

Sequence of gray feldspathic sandstone, arkose, conglomerate, graywacke, siltstone and shale; greenish amygdaloidal basalt flows near middle and base. Thickness 2,000 to 5,000 feet.

Mount Rogers Group including Bakersville Gabbro, Beech Granite, Cranberry Granite, and Roan Gneiss (Precambrian) at surface, covers < 0.1 % of this area

Mount Rogers Group - Metavolcanics, typically purplish and reddish; massive lavas and tuffs, altered rhyolites and quartz latites; strongly foliated; interbedded arkose, shale, and conglomerate. Thickness 1,000 to 3,000 feet; Includes Bakersville Gabbro - Metagabbro, dark, porphyritic; contains diorite, basalt, anorthosite, and diabase; occurs as thin to massive dikes and lenticular masses; Beech Granite - Granite, porphyritic, light-gray to reddish; coarse potash feldspar crystals and clustered interstitial mafics (chloritized biotite and hornblende) give spotted appearance; includes Max Patch Granite; Cranberry Granite - Complex of intertonguing rock types including migmatite, granitic gneisses, monzonite, quartz diorite, greenstone, mica and hornblende schists, abundant granitic pegmatite; and Roan Gneiss - Layered hornblende and garnet gneiss and granitic migmatite with zones of mica schist and amphibolite, foliation commonly contorted; contains numerous granitic and gabbroic dikes.

Hampton Formation (Cambrian) at surface, covers < 0.1 % of this area

Dark greenish-gray, silty and sandy, micaceous shale; numerous layers of medium-grained, feldspathic, thinly bedded sandstone. Thickness 500 to 2,000 feet.

Erwin Formation (Cambrian) at surface, covers < 0.1 % of this area

White, vitreous quartzite, massive, with interbeds of dark-green silty and sandy shale, minor siltstone, and very fine-grained sandstone. Thickness 1,000 to 1,500 feet.

Mount Rogers Formation - Greenstone with interbedded sedimentary rocks (Proterozoic Z) at surface, covers < 0.1 % of this area

Greenstone with interbedded sedimentary rocks; relict plagioclase phenocrysts are prominent in some greenstone.