Open File Report 2011-2 Geologic Map of the Garden City Quadrangle, Virginia Virginia Virginia Division of Geology and Mineral Resources Department of Mines, Minerals and Energy GEOLOGIC MAP OF THE GARDEN CITY QUADRANGLE, VIRGINIA William S. Henika 2011 (SALEM) 79° 52’ 30’’ (STEWARTSVILLE) (ROANOKE) C B 37° 15’ Qal 80° 00’ Qal 34 C 70 Qal Ypg 37° 15’ Qal 8080 18 |a|e |h |s |wb Qal Ypg A 38 |wb|r 18 |h |s |r Ybc DESCRIPTION OF MAP UNITS MIDDLE PROTEROZOIC BASEMENT ROCKS A 65 Qal Qal |wbc|rc 7575 1010 Qal 65 Qal 1515 Qtd 65 QUATERNARY 5555 Charnockitic gneiss - Greenish-gray to dark-green, very coarse grained, porphy- 55 |rc 8888 20 Ybc 1177 17 25 50 |h ritic granitoid composed of orthopyroxene-garnet-bearing groundmass with 2- to 54 35 85 |wb|r Qaf 15 10 Ybc 58 10 35 Qal Modified land - Areas of extensive cut and fill related to construction site prepa- 24 26 ml 3-inch (5- to 7-centimeter) long, potassic feldspar phenocrysts. Grades from 20 20 |h |h 75 |s |h 35 ration and landscaping. coarse-grained protomylonite to mylonite gneiss. Includes Bottom Creek Char- 40 10 78 40 |a|e |wb|r |a nockite Suite of Bartholomew and Lewis (1984). 35 |wb|r 75 25 2020 34 35 |wbc|rc 10 Alluvium - Unconsolidated flood-plain deposits of light-brown to light-gray, 60 12 |e 60 Qal - 60 30 |rc |e well-stratified clay, silt, sand, and gravel. 10 25 Pyroxene granulite gneiss - Medium- to dark-greenish-gray, fine- to medium 19 |wbc 34 65 7 7 |wbc |s 19 |a Qaf 50 |rc |wbc 25 24 |wb Ypg grained, garnet-pyroxene-quartz-feldspar-granulite. Surrounds plutons and is 25 |wbc|rc 80 |r Ypg 25 28 80 |e Boulder streams - Debris-flow deposits in mountainous hollows. Deposits Qal 28 Ybc Qbs also present as xenoliths in Grenville and Iapetan Intrusive suites. Gradational to 32 |wb|r 7 |h |a Qal Ybc Qal Mzd 55 Ypg consist of continuous streams of blocks and boulders with little matrix. Large greenish-gray mylonite and mylonite gneiss along ductile deformation zones that 75 52 |h Jd 15 15 30 25 |u trees on steep slopes in these hollows may indicate a relatively long recurrence |wb|r 25 |uw separate major plutonic units. Correlated with the Lady Slipper Granulite Gneiss, 36 30 10 85 Ybc Qal |rc 20 interval between scouring of debris chutes in storm events. 55 6060 35 |a|e dated at 1130 Ma (Sinha and Bartholomew, 1984). 5 10 75 20 |a|e 85 |a 25 Qal 10 35 |wbc |e 35 25 35 |s 65 72 |a 45 35 15 26 40 |e 20 15 3434 |wb|r 5050 Qaf Alluvial fan deposits - Poorly stratified overlapping debris-flow deposits that HORSEPEN MOUNTAIN SUITE (BARTHOLOMEW AND LEWIS, 1984) Qal |u Qal |wbc|rc 33 Qal consist of dark-reddish-brown clay, silt, sand and gravel matrix with well-rounded Qal 60 33 25 68 |uw 75 35 Ypg 25 68 cobbles and boulders. Mylonitic augen and flaser gneiss - Light- to medium-gray, medium- to coarse- Ypg - 65 Qal Jd 65 40 65 grained muscovite-biotite gneiss and schist that contain polycrystalline quartz |h Qal Mzd 5 3333 Yma |h |s 5 33 Terrace deposits - Dissected remnants of older alluvium and slope deposits that ml |wb|r 40 |s 33 Qtd feldspar augen. occur on gentle slopes and benches above flood plains. Deposits consist of well- 25 25 25 18 6565 fe-208 22 |s Qal 14 rounded quartz pebbles and cobbles with poorly sorted, deeply weathered, dark- 55 17 Massive charnockitic gneiss - Dusky-green, medium- to coarse-grained, hypid- 55 14 2 fe-20765 47 10 C’C’ 65 10 reddish-brown clay, silt, and sand matrix. iomorphic granular to porphyritic, massive to foliated, orthopyroxene-bearing |r fe |a|e 45 Qal Ybc Yhmc |wb fe-206 fe Ybc 47 |uw|u Ylm 15 fe 45 Ybc 6565 charnockitic orthogneiss. 15 fe-112 |wbc|rc fe-205 20 MESOZOIC |s Qal 35 45 |e 60 fe |h 35 40 |a |h |s Jd 35 30 Ysc fe Mzd Ybc 20 35 Ysc Biotite augen gneiss - Dark-gray, medium to coarse-grained, protomylonitic 15 40 40 Qal BLUE R Ylm Diabase dikes - Dark-greenish-gray to black, aphanitic to diabasic, metaluminous ID Qal 45 biotite augen gneiss. Contains large, monocrystalline alkali feldspar porphyro- |r|wb GE Qal Qal 30 45 Jd Ybg F |a 30 30 A T 60 Qal 30 25 to tholeitic basalt containing labradorite, olivine and augite with accessory biotite. clasts. U |e GARDEN CITY FAULT 25 2 L T |s AUL 10 35 Qal Calcite, chlorite, and serpentine are alteration products. Dikes are sub-vertical 15 10 35 30 |rc fe F 52 Qtd 35 50 4545 42 Qal |wbc 35 15 80 42 4545 Qal and typically less than 15 feet (4.5 meters) wide. Sandy Creek Granulite Gneiss (Bartholomew and Lewis , 1984) - Light-gray fe-110 fe |u 20 52 80 46 Qal |h fe-204 CITY |uw 20 15 45 |s fe N 15 45 to dark-grayish-green, medium-to coarse-grained, segregation-banded, biotite 65 fe fe-203 |s 80 Ysc Ysc 65 35 |s fe 80 Ysc PALEOZOIC |e|a 25 30 granofels with localized enclaves of layered pyroxene granulite gneiss. Garnet ARDE 15 30 82 50 5 Qal G 35 15 Ylm 82 5 Qal and hornblende commonly replace earlier pyroxene. Dark-green, uralitic, |uw|u 68 16 68 26 25 UNITS NOT EXPOSED AT SURFACE - ONLY IN CROSS-SECTION amphibole-bearing mylonite gneiss is also common. |e |r|wb 60 35 68 fe-202 60 25 20 Ysc |h|h 30 22 35 |s 70 |a 30 30 70 Millboro Shale and Needmore Formation, undivided - Dark-gray to black, Mylonitic granulite gneiss - dark-green, uralitic, amphibole-bearing mylonite |a |e 5 80 Dmn 8020 45 45 20 45 thin-bedded, slaty-cleaved argillite and light-olive-tan, thin-bedded metasiltstone, gneiss along the Fries fault and related late Paleozoic fault zones. |s 12 15 6565 do-209 1520 Ybg Ylm |e |a 75 1717 48 Ybg with limestone concretions, thin limestone beds, and disseminated sulfides |s 65 Ysc 48 fe-104 65 MzdJd 15 12 (Bartholomew, 1981; Hazlett, 1968; and Henika, 1981 and 1997a). 55 45 fe-201 30 12 45 20 45 |e|a 50 50 20 70 fe-103 30 REFERENCES 62 Lower Devonian, upper Silurian, and upper Ordovician rocks, undivided - 65 65 DSO 20 T 35 45 20 Ybc L Ysc 45 Qaf Qal Ysc Lower Devonian unit includes irregularly bedded, pinkish-white and dark-gray |r|wb |u U Bartholomew, M.J., 1981, Geology of the Roanoke and Stewartsville quadrangles, |wb 50 |uw A 20 chert and grayish-green glauconitic argillite of the Huntersville Chert, and 60 |s |s 70 F |s ID |r 55 70 70 70 35 R G T 70 S 35 45 Virginia: Virginia Division of Mineral Resources Publication 34, 23 p. E E L 45 U F 50 E medium- to very coarse grained, friable, iron-stained, calcareous Ridgely Sand- L AU U 30 I B L A |uw|u R Bartholomew, M.J., and Lewis, S.E., 1984, Evolution of Grenville massifs in the Blue T F 50 stone ( Helderberg Group). Silurian units include tan, white, yellow, and red, fine- 58 F |uw|u 20 50 in Bartholomew, 35 Jd 35 FRIES FAULT 20 |r E 35 Ridge geologic province, southern and central Appalachians, 8585 G 62 Mzd to very coarse grained, poorly cemented Keefer Sandstone, interbedded maroon |h 3535 55 80 45 38 35 35 23 30 D 55 53 385050 20 30 M.J., Force, E.R., Sinha, A.K., and Herz, N., eds., The Grenville Event in the 70 45 I 35 42 hematitic sandstone and greenish-gray argillite of the Rose Hill Formation, and R 20 42 15 75 |s 75 70 40 Appalachians and related topics: Geological Society of America, Special Paper |s |h E 45 70 60 60 10 |h 65 45 7070 60 50 60 40 white, medium- to coarse-grained orthoquartzite of the Tuscarora Formation. 35 U 65 65 L 65 194, P.229, 254. Qal gv Qal 50 Qtd Qal B 34 Upper Ordovician units include grayish-red to greenish-gray argillite, siltstone, 3737 Ylm Butts, Charles, 1941, Geology of the Appalachian Valley in Virginia: Virginia Geologi- 10 Qaf orthoquartzite, and argillaceous limestone of the Juniata Formation (Hazlett, |h Ysc 60 |s 8080 Ybc Mzd cal Survey Bulletin 52, 566 p. |s |s 75 QafQaf 1968; Bartholomew, 1981; Henika 1981 and 1997a). ml 6565 |h Fokin, M.A., 2003, Space-time analysis of magmatism: The igneous record for an Qaf |u Zgr Qtd 4545 Ybc |uw B’ Qtd 5555 Ybc 3434 early Cryogenian plume track in central Appalachian Orogen: M.S. thesis, 45 B’ Martinsburg Formation - Olive and gray, slaty-cleaved, calcareous argillite, Qal |e|a 55 45 3030 Omb 3030 5555 5555 Virginia Polytechnic Institute, Blacksburg, Virginia, 69 p. |u|uw 4040 45 metasiltstone, and metagreywacke (Hazlett, 1968; Bartholomew, 1981; and |s 3535 5555 50 65 7070 50 Hazlett, W.H., Jr., 1968, Structural evolution of the Roanoake Virginia area: Unpub- |s 4545 3030 6060 65 Henika, 1997a). 5555 lished Ph.D. dissertation, Virginia Polytechnic Institute, Blacksburg, Virginia, 266 3535 1010 65 70 3333 Zgr 6565 68 65 3030 68 4545 GARDEN CITY FAULT 35 22 5555 Jd p. 35 30 35 Bays Formation - Light-olive and maroon, fine-grained metagreywacke 2525 |e 35 30 2020 3535 Qal 40 50 Zgr Oba 2525 4545 8080 60 |u Haynes, J.T., 1991, Stratigraphy of the lower part of the Waynesboro Formation (lower 2020 |h 4545 5050 60 6262 42 6565 76 5050 20 20 |uw 40 50 (sublithic sandstone), siltstone, and slaty-cleaved argillite (Hazlett, 1968; 76 4646 6565 6565 42 3838 4545 70 63 and middle Cambrian) near Buchanan, Botetourt County, Virginia: Virginia 25 |e|a 1515 4747 35 70 Mzd Bartholomew, 1981; and Henika, 1997a).