Geologic units in Granville county, North Carolina

Felsic Metavolcanic Rock (Cambrian/Late Proterozoic) at surface, covers 23 % of this area

Metamorphosed dacitic to rhyolitic flows and tuffs, light gray to greenish gray; interbedded with mafic and intermediate metavolcanic rock, meta-argillite, and metamudstone.

Metamorphosed Granitic Rock (Cambrian/Late Proterozoic) at surface, covers 21 % 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.

Metavolcanic Rock (Cambrian/Late Proterozoic) at surface, covers 16 % of this area

Interbedded felsic to mafic tuffs and flowrock.

Newark Supergroup, Chatham Group; Chatham Group, Undivided (Triassic) at surface, covers 16 % of this area

Conglomerate, fanglomerate, sandstone, and mudstone. Conglomerate and fanglomerate shown by pattern.

Metamorphosed Gabbro and Diorite (Paleozoic/Late Proterozoic) at surface, covers 8 % of this area

Foliated to massive.

Metavolcanic-Epiclastic Rock (Cambrian/Late Proterozoic) at surface, covers 7 % of this area

Metamorphosed argillite, mudstone, volcanic sandstone, conglomerate, and volcanic rock.

Biotite Gneiss and Schist (Cambrian/Late Proterozoic) at surface, covers 3 % of this area

Inequigranular and megacrystic; in places contains garnet; interlayered and gradational with mica schist and amphibolite; includes small masses of granitic rock.

Newark Supergroup, Chatham Group; Diabase (Jurassic) at surface, covers 2 % of this area

Diabase - dikes and sills, gray to black.

Metamorphosed Quartz Diorite (Paleozoic/Late Proterozoic) at surface, covers 2 % of this area

Foliated to massive.

Felsic Mica Gneiss (Cambrian/Late Proterozoic) at surface, covers 0.6 % of this area

Interlayered with graphitic mica schist and mica-garnet schist, commonly with kyanite; minor hornblende gneiss.

Granitic Rock (Permian/Pennsylvanian) at surface, covers 0.3 % of this area

Megacrystic to equigranular. Castalia, Lillington, Medoc Mountain, Sims, Contentnea Creek (?), and Elm City (?) intrusives.

Meta-ultramafic Rock (Paleozoic/Late Proterozoic) at surface, covers 0.2 % of this area

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

Phyllite and Metatuff (Proterozoic Z) at surface, covers 0.1 % of this area

Includes light-gray, very fine-grained, foliated chlorite-sericite phyllite and phyllitic metamudstone, and dark-gray to white, fine- to medium-grained lithic and crystal dacite metatuff. Includes Goshen schist of Laney (1917).

Aaron Slate (Proterozoic Z) at surface, covers < 0.1 % of this area

Very-light-gray, fine-grained, bedded volcaniclastic sediments, conglomerate, lithic feldspathic arenite, micaceous sandstone, siltstone, phyllite, argillite, and vitric tuff, with minor greenstone. Lithic fragments and relict euhedral crystals are common. The lower part of the unit is dominantly grayish-green slate interbedded with light-gray to grayish-green micaceous metasandstone; bedding is conspicuous and graded-bedding is common. The unit grades upward to bedded light-gray to moderate-red phyllite, metasandstone and slate.

Felsic Volcanic Rocks (Proterozoic Z) at surface, covers < 0.1 % of this area

Very-light-gray, fine- to medium-grained crystal, lithic, and lithic-crystal andesitic metatuff with minor light-gray to white, fine-grained metasedimentary interbeds.

Meta-ultramafic Rock (Paleozoic/Late Proterozoic) at surface, covers < 0.1 % of this area

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

Virgilina Greenstone (Proterozoic Z) at surface, covers < 0.1 % of this area

Virgilina greenstone (Laney, 1917). Grayish-green, fine- to coarse-grained basaltic tuff, metavolcanic breccia, and porphyritic to amygdaloidal greenstone, with minor interlayered metasedimentary rocks. Hydrothermally mineralized zones occur within the greenstones; these contain bornite, chalcocite, and chalcopyrite, and have been mined for copper. Mineralogy: plagioclase + hornblende + chlorite + epidote + calcite + apatite + quartz + opaque minerals. Geophysical signature: linear positive magnetic anomaly. Watson (1911) used the term Virgilina Group for a wide belt of rocks in the vicinity of Virgilina, Virginia. Mafic metavolcanic rocks in this sequence were named Virgilina greenstone, and felsic metavolcanic rocks and associated metasedimentary rocks were named Aaron slate by Laney (1917). Kreisa (1980) refined Laney's stratigraphy in defining the Aaron Formation as containing upper and lower members equivalent to Laney's Aaron slate, and a middle member equivalent to the Virgilina greenstone. The stratigraphy was further modified by Harris and Glover (1985), who combined the middle and upper members of Kreisa's Aaron Formation to make the Virgilina Formation. Virgilina greenstone is herein used in the sense of Laney (1917), but is equivalent to the middle member of the Aaron Formation of Kreisa (1980), and the lower portion of the Virgilina Formation of Harris and Glover (1985) (Figure 2).

Amphibolite (Cambrian/Late Proterozoic) at surface, covers < 0.1 % of this area

Metamorphosed mafic extrusive and intrusive rock; includes hornblende gneiss, thin layers of mica schist, and small nonlayered masses of metadiorite and metagabbro.

Hornblende-plagioclase Gabbro (Proterozoic) at surface, covers < 0.1 % of this area

Dark-grayish-green, coarse- to medium-grained, massive to foliated metagabbro. Mineralogy: amphibole + plagioclase + clinopyroxene + quartz + biotite + muscovite + epidote ± magnetite. Geophysical signature: small circular positive magnetic anomalies. Plutons of these gabbros intrude interlayered mafic and felsic metavolcanic rocks.

Metamorphosed Gabbro and Diorite (Paleozoic/Late Proterozoic) at surface, covers < 0.1 % of this area

Foliated to massive.

Phyllite and Metasiltstone (Proterozoic Z) at surface, covers < 0.1 % of this area

Dominantly light-gray, schistose chlorite-sericite phyllite and phyllitic metasiltstone with a well-developed phyllitic or slaty cleavage; includes minor interlayered mafic and felsic metavolcanic rocks.

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

White to light-gray, medium- to coarse-grained, faintly foliated, locally porphyritic; ranges from granodiorite to quartz diorite. Mineralogy: quartz + plagioclase + biotite + microcline. This unit includes the Vance pluton of Horton and others (1993), dated at 571±17 Ma (U-Pb zircon; LeHuray, 1989).