Geologic units in Caswell county, North Carolina

Biotite Gneiss and Schist (Cambrian/Late Proterozoic) at surface, covers 38 % of this area

Inequigranular and megacrystic; abundant potassic feldspar and garnet; interlayered and gradational with calc-silicate rock, sillimanite-mica schist, mica schist, and amphibolite. Contains small masses of granitic rock.

Metamorphosed Granitic Rock (Cambrian/Late Proterozoic) at surface, covers 22 % of this area

Megacrystic, well foliated; locally contains hornblende. Chapel Hill, Chatham, Farrington, Meadow Flats, Mt. Moriah, Parks Crossroads plutons, and Roxboro and Vance County suites.

Felsic Mica Gneiss (Cambrian/Late Proterozoic) at surface, covers 13 % of this area

Interlayered with biotite and hornblende gneiss and schist.

Metamorphosed Gabbro and Diorite (Paleozoic/Late Proterozoic) at surface, covers 13 % of this area

Foliated to massive.

Phyllite and Schist (Cambrian/Late Proterozoic) at surface, covers 6 % of this area

Minor biotite, pyrite, and sillimanite; includes minor quartzite.

Mafic Metavolcanic Rock (Cambrian/Late Proterozoic) at surface, covers 3 % of this area

Metamorphosed basaltic flows and tuffs, dark green to black; interbedded with felsic and intermediate metavolcanic rock and metamudstone.

Shelton Granite Gneiss (Silurian) at surface, covers 3 % of this area

Poorly foliated; lineated granitic to quartz monzonitic gneiss.

Granitic Rock (Permian/Pennsylvanian) at surface, covers 1 % of this area

Megacrystic to equigranular. Churchland Plutonic Suite (Western group) - Churchland, Landis, and Mooresville intrusives.

Metamorphosed Granitic Rock (Cambrian/Late Proterozoic) at surface, covers 1 % of this area

Megacrystic, well foliated; locally contains hornblende.

Meta-ultramafic Rock (Paleozoic/Late Proterozoic) at surface, covers 0.4 % of this area

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

Diorite Gneiss (Proterozoic) at surface, covers < 0.1 % of this area

White to gray, fine- to medium grained, massive to layered quartz diorite gneiss, contains minor biotite and epidote; lenses of gray to black, medium-grained, layered hornblende-plagioclase gneiss and quartz-epidote clinopyroxene- hornblende-plagioclase gneiss occur locally (Tobisch, 1972).

Interlayered Mafic and Felsic Metavolcanic Rocks - Quartz-muscovite schist and gneiss. (Cambrian) at surface, covers < 0.1 % of this area

Quartz-muscovite schist and gneiss; Heterogenous layered assemblage correlates with the Chopawamsic Formation and Ta River Metamorphic Suite, on strike to the northeast, and in traceable into the Milton belt in North Carolina (Geologic Map of North Carolina, 1985). Quartz muscovite schist and gneiss. Very-light-gray to light-bluish-gray, fine- to medium-grained, layered kyanite mica schist, kyanite and sillimanite quartzite, and interlayered biotite-garnet schist. Mineralogy: quartz + muscovite + plagioclase ± biotite ± garnet ± sillimanite ± kyanite ± magnetite. Includes the schist and gneiss unit of Tobisch (1972), and muscovite-quartz schist of Baird (1989, 1991).

Interlayered Mafic and Felsic Metavolcanic Rocks - Amphibolite, hornblende-biotite gneiss, and schist. (Cambrian) at surface, covers < 0.1 % of this area

Amphibolite, hornblende-biotite gneiss, and schist.; Heterogenous layered assemblage correlates with the Chopawamsic Formation and Ta River Metamorphic Suite, on strike to the northeast, and in traceable into the Milton belt in North Carolina (Geologic Map of North Carolina, 1985). Amphibolite, hornblende-biotite gneiss and schist. Black to moderate-olive-brown, medium- to coarse-grained, lineated and foliated; light-greenish-gray quartz-epidote stringers are common. Mineralogy: hornblende + tremolite-actinolite + oligoclase + biotite + epidote + garnet. Includes Blackwater Creek Gneiss and Catawba Creek amphibolite member of Hyco Formation of Baird (1989), hornblende gneiss of LeGrand (1960), gneiss unit of Kreisa (1980), and dominantly mafic-composition units mapped by Nelson (1992). Amphibolite is interlayered with biotite gneiss, as discussed above.

Interlayered Mafic and Felsic Metavolcanic Rocks - Foliated felsite (Cambrian) at surface, covers < 0.1 % of this area

Foliated felsite; Heterogenous layered assemblage correlates with the Chopawamsic Formation and Ta River Metamorphic Suite, on strike to the northeast, and in traceable into the Milton belt in North Carolina (Geologic Map of North Carolina, 1985). Foliated felsite. Grayish-orange-pink to white, fine- to medium-grained, foliated to granular metavolcanic rocks range in composition from rhyolite to dacite. Includes muscovite feldspar- quartz schist, gneiss and granofels; massive crystal metatuff; welded ashflow tuff; and, inequigranular metavolcanic breccia. Relict primary volcanic textures are recognizable where metamorphic grade is low (Henika, 1975; 1977). This unit includes felsic gneiss with less common mafic and rare calcareous gneiss mapped by Tobisch (1972), in part the metamorphosed volcanic sequence of Gates (1981), and dominantly felsic-composition units mapped by Nelson (1992). The unit contains numerous granitic dikes, sills, and lit-par-lit injections where it occurs in close proximity to Shelton Formation (Ost). Felsites occur interlayered with amphibolite, amphibole gneiss and schist (Cmv), quartzofeldspathic biotite gneiss (Cbg), sillimanite-quartz-muscovite schist and gneiss (Csg), and ferruginous quartzite (Cfq).