Geologic map of the Cedar Grove 7.5-minute quadrangle, Orange, Person and Caswell Counties, North Carolina

DEPARTMENT OF ENVIRONMENT AND NATURAL RESOURCES DIVISION OF LAND RESOURCES JAMES D. SIMONS, STATE GEOLOGIST This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program 79 07' 30" 36 15' 00' Zgr-gd — Prospect Hill pluton 3gd Interpreted to be related to the ca. 546 Ma Roxboro pluton, (Wortman et al.. 2000) Virgilina deformation - ca. 578 to 554 Ma (Pollock, 2007) East Farrington pluton, U-Pb, ca. 579 Ma (Tadlock and Loewy, 2006) Chapel Hill, Hillsborough, Efland, Caldwell and Cedar Grove Areas Aaron Formation Rougemont, Lake Michie and Virgilina Areas 7 Aaron Formation, Youngest Detrital Zircon, ca. 588 Ma (Pollock, 2007) Esrween Ranse jr and Slef Ciy ‘flow banded rhyolite”, U-Pb ca. 633 Ma (Wortman et al., 2000) Chapel Hill granite, U-Pb,' ca. 633 Ma (Wortman et al., 2000) Zefg-m ZefP Zabit ?AaronlHyco Formation? Ze/p ^ ca 615 maHyco Formation -‘Upper’ Zdsi Zft Zgd Zdi Zgr Zgd сабЗОта Hyco formation - ‘Lower’ ? - basemeil no! exposed Aaron Formation, Youngest Detrital Zircon, ca. 578 Ma (Samson et al., 2001) Hyco Formation Dacitic Tuff, U-Pb, ca. 616 Ma (Wortman et al., 2000) Flat River Complex Diorite, U-Pb, ca. 614 Ma (Wortman et al., 2000) Flat River Complex Granite, U-Pb, ca. 613 Ma (Wortman et al., 2000) Preliminary correlation of geologic units in the Orange County, NC area. Includes geologic units from the Chapel Hill, White Cross, Hillsborough, Efland, Farrington and Northwest Durham geologic maps. Units are assigned to the Hyco Formation of the Virgilina sequence of Harris and Glover (1988). Equal Area Equal Area Equal Area Schmidt Net Projection of Contoured Poles to Foliation, and Cleavage Contour Interval = 2% N = 205 Unidirectional Rose Diagram of Foliations and Cleavage N = 205 Outer Circle= 25% Mean dir =223 Equal Area Equal Area Equal Area Schmidt Net Projection of Poles to Primary Layering, Bedding, and Welding/Compaction Foliation. N=19 Unidirectional Rose Diagram of Primary Layering, Bedding, Welding/Compaction Foliation. N = 19; Outer circle = 21%; Mean dir = 233 Equal Area Equal Area Unidirectional Rose Diagram of Joints N = 344 Outer Circle = 7% Mean Direction = 210 Unidirectional Rose Diagram of Pdad and Padid Dike Trends N = 20 Outer Circle = 15% Mean Direction = 208 TRAVERSE MAP - traverse by foot - traverse by car 36 07' 30" 36” 1 5' 00" II fr/ty 'll /87 7y 89/. - • % 6sy G V yy • cAW J w74z( Г Ж 7 ШтгшУ 7 /уУ\ ( Qal V JfPx/ l Pdad у Padid CZtgd CZgr-gd Zdi Zgd-gb 79 15' 00" Base topographic map is digital raster graphic image of the Cedar Grove 7.5-minutc quadrangle ( 1 967), North Carolina State Plane NAD 83 meters coordinate system, Lambert Conformal Conic projection. 81/2 151 MILS 0.5 SCALE 1:24 000 0 Geology mapped from August 2008 through June 2009 and September 2009 through May 20 1 0. i Miles 1,000 500 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 — I I I I I I - I Feet 1 09' 20 MILS 0.5 1 l Kilometers 2000 MAGNETIC NORTH DECLINATION FROM ADJACENT CALDWELL 7.5-MINUTE TOPOGRAPHIC MAP 750' -i -1250' — -3250' Lynch Wades Creek Dead End I Qal l Caswell County State Hwys 49 & 86 \ jL Orange County CONTOUR INTERVAL 10 FEET South Hyco Creek Вата Rd. Hurdle Mills Rd. MAP LOCATION A' Zdlt CZgr-gd Padid Padid CZtgd I— 750' CZtgd — -1250' -3250' В 720' r— Lynch Rd. I Harmony Back Church Rd. Creek l J Harmony Church Rd. Poteat Rd. Mill Creek Rd. cross section scale 1 :24 000 no vertical exaggeration Governor Scott Rd. Efland Cedar Grove Rd. Qal I I I 1 I Qal Qal West Fork East Fork of the of the Eno River Eno River I I I 7 " r-\~i ▼ B' -1320' - Pdad / dikes CZtgd -3320' \ Zft Qal ’ Qal L _ L - - 720 — -1320' -3320' GEOLOGIC MAP OF THE CEDAR GROVE 7.5-MINUTE QUADRANGLE, ORANGE, PERSON and CASWELL COUNTIES, NORTH CAROLINA By Heather D. Hanna, Philip J. Bradley and Norman K. Gay Digital representation by Michael A. Medina, Heather D. Hanna and Philip J. Bradley 20 Ю Zdsi Ze/p Zft Zdlt NORTH CAROLINA GEOLOGICAL SURVEY OPEN FILE REPORT 2010-02 Revision-01 (2010) DESCRIPTION OF MAP UNITS All pre-Mesozoic rocks of the Cedar Grove quadrangle have been metamorphosed to at least the chlorite zone of the greenschist metamorphic facies. Many of the rocks display a weak or strong metamorphic foliation. Although subjected to metamorphism, the rocks retain relict igneous, pyroclastic, and sedimentary textures and structures that allow for the identification of protolith rocks. As such, the prefix "meta” is not included in the nomenclature of the pre-Mesozoic rocks described in the quadrangle. The nomenclature of the International Union of Geological Sciences subcommission on igneous and volcanic rocks (IUGS) after Streckeisen (1973 and 1979) is used in classification and naming of the units. The classification and naming of the rocks is based on relict igneous textures, modal mineral assemblages, or normalized mineral assemblages when whole-rock geochemical data is available. Past workers in the Cedar Grove quadrangle and adjacent areas (Allen and Wilson. 1968 and Newton. 1983) have used various nomenclature systems for the igneous rocks. The raw data of these earlier workers was recalculated and plotted on ternary diagrams and classified based on IUGS nomenclature. Pyroclastic rock terminology follows that of Fisher and Schminke (1984). Sedimentary Units Qal - Alluvium: Unconsolidated poorly sorted and stratified deposits of angular to subrounded clay, silt, sand and gravel- to cobble-sized clasts, in stream drainages. May include point bars, terraces and natural levees along larger stream floodplains. Structural measurements depicted on the map within Qal represent outcrops of crystalline rock inliers surrounded by alluvium. Intrusive and Meta-Intrusive Units Jd - Diabase: Black to greenish-black, fine- to medium-grained, dense, consists primarily of plagioclase, augite. and may contain olivine. Occurs as dikes up to 100 ft wide. Diabase typically occurs as spheroidally weathered boulders with a grayish-brown weathering rind. Red station location indicates outcrop or boulders of diabase. Jfp - Felsic porphyry: Dark gray, aphanitic groundmass with fine-grained disseminated quartz. Feldspar phenocrysts range from 2 to 5 mm. Weathered surfaces display pockmarked texture from weathering of feldspar phenocrysts and/or mineral filled amygdules. Dike trends are inferred. Pdad - Dacitic dikes: Dark gray to gray, finely crystalline, and locally weakly plagioclase porphyritic dacite dikes ranging from less than one foot to several feet wide. Dike trends are inferred. Padid - Andesite to diorite dikes: Melanocratic to Mesocratic (Cl -50 to greater than 50), dark green to green gray, aphanitic to medium-grained, metamorphosed andesite to diorite. Andesites and diorites are locally plagioclase porphyritic. Typically occur in map area as resistant spheroidal boulders. Locally maybe basaltic to gabbroic. Dike trend lines indicated were strike of dike measured in outcrop or interpreted from adjacent stations. Occur as infestation in Ztgd unit and are present in many more locations than displayed on map. Dike trends are inferred. CZfgd - Propecf Hill tonalitic granodiorite pluton: Unfoliated to locally very weakly foliated, leucocratic (Cl less than 10), very light gray to yellowish gray, medium- to coarse-grained, hypidiomorphic granular, metamorphosed tonalitic granodiorite to tonalite. Mafic minerals present in rock are most commonly biotite intergrown with chlorite and/or hornblende intergrown with actinolite. Biotite books (± magnetite intergrowths) up to 2 cm commonly occur in north of Cedar Grove Quadrangle. Locally muscovite bearing. Cross cutting pegmatitic dikes of similar mineralogy present in some areas. Locally biotite forms (magmatic?) foliation. Weathering of rock produces distinctive coarse quartz sand grains in soil. Andesite to diorite dikes (Zadid) are common throughout the pluton and typically occur as resistant spheroidal boulders. Pluton map pattern truncates Virgilina sequence volcanics and pluton contains foliated xenoliths of volcanic rocks; as such, the pluton is interpreted to be related to the Ca. 546 ma Roxboro pluton (Wortman et al.. 2000). CZgr-gd - Granite to granodiorite of the Prospect Hill pluton: Composite pluton of dominantly medium-grained, hornblende granodiorite; lesser amounts of medium-grained hornblende diorite, plagioclase porphyritic granodiorite, fine-grained granodiorite, and diorite; minor amounts of fine-grained gabbro. Fine-grained granodiorite and diorite are typically green in hand sample from sausseritization of plagioclase. Hornblende is typically altered to chlorite and actinolite masses. Zdi - Diorite: Mesocratic (Cl— 50), medium gray, fine- to medium-grained, hypidiomorphic granular diorite. Major minerals include plagioclase and hornblende. Plagioclase crystals are typically sericitized and saussuritized and can occur as phenocryst up to 2 cm diameter. Hornblende is typically altered to chlorite and actinolite masses. Locally hornblende forms (magmatic?) foliation. Includes minor green, fine-grained microdiorite to andesite. Dikes attributed to CZtgd unit intrude diorite bodies locally. Zgd-gb - Granodiorite to gabbro: Composite pluton of dominantly medium-grained, hornblende granodiorite; lesser amounts of medium-grained hornblende diorite, plagioclase porphyritic granodiorite, fine-grained granodiorite. and diorite; minor amounts of fine-grained gabbro. Fine-grained granodiorite and diorite are typically green in hand sample from sausseritization of plagioclase. Hornblende is typically altered to chlorite and actinolite masses. Zdsi - Dacitic shallow intrusive: Grayish-green to light green, plagioclase poiphyritic dacite with a granular-textured groundmass to very fine-grained granodiorite (with intrusive texture visible with 7x hand lens). Contains lesser amounts of fine- to medium grained granodiorite. Plagioclase phenocrysts typically range from 1 mm to 4 mm. Black colored amphibole, when visible, occurs as phenocrysts (less than 1 mm to 1 mm) and as intergrowths with plagioclase. Amphibole intergrowths distinguish rock from fine-grained tuffs. Enclaves of dark gray, plagioclase poiphyritic dacite are common and at times give rock a psuedo-clastic appearance. Locally andesite to diorite and xenoliths of tuffs are present. Metavoicanic Units Ze/p - Mixed epiclastic-pyroclastic rocks: Mixed epiclastic-pyroclastic rocks: Grayish-green to greenish-gray; tuffaceous sandstones, conglomeratic sandstones, siltstones and minor phyllite. The siltstones typically are weakly phyllitic. Contains lesser amounts of fine to coarse tuff and lapilli tuff. Minor andesitic to basaltic lavas and tuffs present. Silicified and/or sericitized altered rock similar to Zat unit are present near contacts with other units. Distinctive plagioclase + quartz crystal tuff present in lower zones of unit near contact with Zft unit. Zft - Felsic tuffs: Grayish- green to greenish-gray and silvery-gray, massive to foliated, volcaniclastic pyroclastic rocks consisting of fine- to coarse tuffs, lapilli tuffs and minor welded tuffs. Layering ranges from massive to thinly bedded. Contains lesser amounts of volcaniclatic sedimentary rocks consisting of volcanic sandstones, and greywackes with minor siltstones and phyllite. Minor andesitic to basaltic lavas and tuffs. Distinctive plagioclase + quartz crystal tuff present in unit in higher stratigraphic zones near the Ze/p unit. Zdlt - Dacitic lavas and tuffs: Distinctive dark-gray to black, siliceous, cry ptocry stall ine dacite. poiphyritic dacite with plagioclase ± quartz phenocrysts, and flow banded dacite. Welded and non- welded tuffs associated with the lavas include: greenish-gray to grayish-green, fine tuff, coarse plagioclase crystal tuff; lapilli tuff; and tuff breccia. The dacites are interpreted to have been coherent magma that were extrusive or very shallow intrusions associated with dome formation. The tuffs are interpreted as episodic pyroclastic flow deposits, air fall tuffs or reworked tuffs generated during formation of dacite domes. Wortman et al. (2000) report a 632.9 +2.6/-1.9 Ma zircon date from a sample within the unit in the Chapel Hill quadrangle. References: Allen. E.R. and Wilson. W.F., 1968, Geology and mineral resources of Orange County. North Carolina: Division of Mineral Resources. North Carolina Department of Conservation and Development. Bulletin 81, 58 p. Fisher, R.V.. and Schmincke H.-U.. 1984, Pyroclastic rocks, Berlin. West Germany, Springer- Verlag, 472 p. Harris, C.. and Glover, L. 1988, The regional extent of the ca. 600 Ma Virgilina deformation: implications of stratigraphic correlation in the Carolina terrane. Geological Society of America Bulletin, v. 100. pp. 200-217. Newton. M.C., 1983. A late Precambrian resurgent cauldron in the Carolina slate belt of North Carolina, U.S.A.. M.S. thesis, Virginia Polytechnic Institute and State University, 89 p. Pollock. J. C., 2007, The Neoproterozoic-Early Paleozoic tectonic evolution of the peri-Gondwanan margin of the Appalachian orogen: an integrated geochronological, geochemical and isotopic study from North Carolina and Newfoundland. Unpublished PhD dissertation. North Carolina State University. 194 p. Streckeisen. A.L.. 1973, Plutonic rocks: Classification and nomenclature recommended by the IUGS subcommission on the systematics of igneous rocks: Geotimes, v. 18, p.26-31. Streckeisen, A.L., 1979, Classification and nomenclature of volcanic rocks, lamprophyres, carbonatites, and melilitic: Recommendations and suggestions of the IUGS subcommission on the systemics of igneous rocks. Geology, v. 7, p. 331-335. Tadlock. K.A. and Loewy, S.L., 2006. Isotopic characterization of the Farrington pluton: constraining the Virgilina orogeny, in Bradley. P.J., and Clark. T.W.. editors. The Geology of the Chapel Hill. Hillsborough and Efland 7.5-minute Quadrangles, Orange and Durham Counties, Carolina Terrane, North Carolina, Carolina Geological Society Field Trip Guidebook for the 2006 annual meeting, pp. 1 7-21. Wortman. G.L.. Samson. S.D.. and Hibbard. J.P.. 2000. Precise U-Pb zircon constraints on the earliest magmatic history of the Carolina terrane. Journal of Geology, v. 108, pp. 321-338. EXPLANATION OF MAP SYMBOLS CONTACTS Lithologic contacts - Distribution and concentration of structural symbols indicates degree of reliability. - contact - location inferred . contact - location concealed . . . . . . gradational contact - location inferred - diabase dike - location inferred in cross section, interpreted fold form lines of non-cylindrical asymmetric folds - o - - - - ft- — - cross section line inferred fold hinge of plunging overturned anticline; dotted where concealed inferred fold hinge of plunging overturned syncline; dotted where concealed inferred fold hinge of doubly plunging overturned syncline; dotted where concealed in cross section, inferred axial trace of large-scale fold PLANAR FEATURES Observation sites are centered on the strike bar or are at the intersection point of multiple symbols. Planar feature symbols may be combined with linear features. Г / ’ 74/ ^ ii -i 36 07' 30" -34) /, 8У 79 07' 30" X strike and dip of primary bedding and layering strike and dip of overturned primary bedding and layering strike and dip of primary volcanic compaction and/or welding foliation strike and dip of foliation vertical foliation diabase station location X strike and dip of cleavage / vertical cleavage 7У strike and dip of spaced cleavage 88 strike and dip of high strain foliation X strike and dip of foliation of xenolith within Prospect Hill pluton vertical foliation of xenolith within Prospect Hill pluton 84 strike and dip of magmatic (?) foliation 66y defined by aligned biotite or amphibole within the Prospect Hill pluton © observation station location strike and dip of joint У vertical joint □ observation station location in tonalitic granodiorite unit with conspicuous coarse quartz grains in soil This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program, award number 08HQAG01 00 and G09AC001 83. The views and conclusions contained in this document arc those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government. Disclaimer: This Open- File report lias been reviewed for confonnity with the North Carolina Geological Survey editorial standards. Scan with smartphone for link to GeoPDF of map. Third party App required. GEOLOGIC MAP OF THE CEDAR GROVE 7.5-MINUTE QUADRANGLE, ORANGE, PERSON AND CASWELL COUNTIES, NORTH CAROLINA NCGS OPEN FILE REPORT 2010-02 Revision - 01 (2010)