Geologic map of the Farrington 7.5-minute quadrangle, Chatham, Orange and Durham Counties, North Carolina

DEPARTMENT OF ENVIRONMENT AND NATURAL RESOURCES DIVISION OF LAND RESOURCES This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program NORTH CAROLINA GEOLOGICAL SURVEY OPEN FILE REPORT 2007-03 GEOLOGIC MAP OF THE FARRINGTON 7.5-MINUTE QUADRANGLE, CHATHAM, ORANGE AND DURHAM COUNTIES, NORTH CAROLINA BY PHILIP J. BRADLEY, NORMAN K. GAY, RANDY BECHTEL AND TIMOTHY W. CLARK Digital representation by Michael A. Medina, Philip J. Bradley and Norman K. Gay 79° 07' 30" 2007 79° 00 35° 52' 30" 35° 45' Trcs/si1 raM Trcs/si1 •• Zablt Zwfd © Zablt Zablt Zablt B. Everett Jordan Lake Trcs/si2 Trcs/si2 Zablt l50 ' 7f.t . f)50, Zf,t"bw . Trcs/si2 ) JORDAN lake! Jd V — ' \ 4 STATE RECREATION ARE 7 Zablt Zablt 35° 52' 30" 35° 45' DESCRIPTION OF MAP UNITS All pre-Mesozoic rocks of the Farrington 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 Farrington quadrangle (Eligman, 1987 and Wagener, 1964 and 1965) 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 clay, silt, sand and gravel to cobble-sized clasts, subrounded to angular, deposited in drainages. K/Tu - post-Chatham Group undifferentiated sediments: Yellowish-orange to brownish-yellow to yellowish-gray, unconsolidated to friable unit that consists of distinctive subrounded to well rounded granules, pebbles and small cobbles of white- to rose-colored quartz interlayered with clay, sandy- clay and clayey-sand. Lesser amounts of moderately indurated, yellowish-white, medium- to coarse-grained arkosic sandstone present. Unit is exposed on shores of B. Everett Jordan Lake and the southern portion of the Farrington peninsula south of Lystra Road. Unit is in unconformable contact with Triassic sediments. Trcs/si1 Trcs/sil - Chatham Group Lithofacies Association I: Pinkish-gray, light-gray, and light-tan; fine- to coarse-grained, micaeous, slightly clayey, moderately poor to moderately well sorted, subangular to subrounded arkose and lithic arkose; maroon, very silty, micaeous, moderately well sorted, fine-grained sandstone; and maroon, massive, and thickly laminated, bioturbated, micaeous to very micaeous, siltstone and mudstone. Muscovite flakes up to 3 mm diameter are common especially in the siltstone. Fine-grained flakes of biotite in the arkose and lithic arkose is a distinctive accessory. Randomly oriented and vertical, cylindrical structures often filled with pale-green, fine-grained, quartz sandstone are interpreted as burrows. Bedding, when observed, is parallel to slightly wavy, occurring as thick laminations to thinly bedded (0.5 cm to 5 cm). These rocks are assigned to the Lithofacies Association I of Hoffman and Gallagher, 1991 and Watson, 1998. The clastic rocks of Lithofacies Association I are interpreted to have been deposited in a braided stream fluvial system. Trcs/si2 Trcs/si2 - Chatham Group Lithofacies Association II: Grayish-pink to pale-red, micaeous, coarse- to very coarse-grained, pebbly, cross-bedded lithic arkose interbedded with maroon, micaeous mudstone. Good outcrops typically exhibit cyclical fining upward depositional sequences. Best exposures are present near intersection of Martha’s Chapel Road and B. Everett Jordan Lake (see Stop 3 in Clark et al., 2001). These rocks are assigned to the Lithofacies Association II of Hoffman and Gallagher, 1991 and Watson, 1998. The clastic rocks of Lithofacies Association II are interpreted to have been deposited in a meandering stream fluvial system. Intrusive and Meta-Intrusive Units ,"Jd# Jd - diabase: Black to greenish-black, fine- to medium-grained, dense, consists primarily of plagioclase, augite, and +/- olivine. Occurs as dikes up to 100 ft wide. Diabase typically occurs as spheriodally weathered boulders with a grayish-brown weathering rind. Red station location indicates outcrop or boulders of diabase. Zhm - Hunter Mountain dike: Distinctive, greenish-gray, plagioclase porphyritic (with plagioclase phenocrysts up to 1 cm long) granodiorite to diorite. Matrix is fine-grained consisting of interlocking plagioclase and amphibole (possibly pyroxene) crystals up to 1 mm. Correlated with the Hunter Mountain dike complex of Hauck ( 1977). Purple station location indicates outcrop or boulders. East Farrington pluton The East Farrington pluton is composed of 4 distinct granitoid facies based on textural characteristics. U-Pb zircon geochronologic data (Tadlock and Loewy, 2006) indicate that the East Farrington pluton is ca. 579 Ma. Zefg-m Zefg-m - East Farrington pluton main facies: Unfoliated, orange pink to pinkish-gray to gray, medium- to coarse-grained, equigranular to slightly porphyritic, amphibole (va. hornblende?) granite. Amphibole content varies from approximately 5 to 10% by volume and occurs locally as dark green, elongate crystals up to 1 .5 cm long and amorphous intergrowths with feldspar and quartz up to 0.5 cm diameter. Dark gray xenoliths/enclaves up to 8 cm in diameter are common. Grain size becomes finer and xenoliths/enclaves larger near the pluton edge. Cavities, <lmm in diameter, with euhedral terminating crystals are common in some specimens. Weakly foliated outcrops are present along Pokeberry Creek and several other locations. In thin section, the main facies can be separated into two groups: 1) rocks with a porphyritic texture with orthoclase and plagioclase phenocryts in a groundmass of intergrown orthoclase, plagioclase and quartz with a granophyric texture (micrographic texture) and 2) porphyritic and equigranular rocks consisting of orthoclase, plagioclase and quartz without a granophyric texture in matrix. The two varieties appear to be intermingled throughout the study area. Zefg-ml - East Farrington pluton main facies variety 1: Identical to main facies but with dark green, chlorite masses up to 4 mm diameter. In thin section, the chlorite masses are intergrowths of chlorite and dark green, fibrous amphibole. - Zefg-2 Zefg-2 - East Farrington pluton porphyritic granite: Gray, fine-grained groundmass with pink- and white-colored phenocrysts (1 mm to 4 mm) of orthoclase and plagioclase, granite. Anhedral to acicular-shaped, dark green, amphiboles (<1 mm to 4 mm long) present in groundmass of quartz and orthoclase and as intergrowths with orthoclase and plagioclase phenocrysts. Present as several map scale bodies and as outcrop scale enclaves surrounded by East Farrington pluton main facies rock. ,;:эдэрз> Zefg-3 - East Farrington pluton fine-grained granite: Orange pink, fine-grained granite. Similar texture and mineralogy to East Farrington pluton main facies but with an overall finer-grained texture. White feldspar phenocrysts compose <5% of rock. V V V V V ' ■ Zefg-4 v V V V V V ' Zefg-4 - East Farrington pluton gray granitoid: Unfoliated to foliated, light gray to light greenish -gray, medium-grained granite to granodiorite. White-colored feldspar content is greater than pink feldspars. Foliated specimens have visible white mica growth and less pink feldspars than unfoliated specimens. Foliated rock is present along portions of Pokeberry Creek, Pritchards Mill Creek and Cumbo Branch. Zefg-5 Zefg-5 - East Farrington pluton satellite granite: Unfoliated, orange pink to pinkish-gray to gray, fine- to medium-grained, equigranular, amphibole (va. hornblende?) granite. Similar to East Farrington pluton main facies but overall finer-grained. Zwfd Zwfd - West Farrington pluton diorite: Unfoliated, medium-grained hornblende diorite. Zdi Zdi - Diorite: Greenish-gray to gray, medium-grained, equigranular, hornblende diorite. Major minerals include plagioclase and hornblende. Greenish-white plagioclase crystals compose up to 50% of the rock and are typically sericitized and saussuritized. Hornblende is typically altered to chlorite and actinolite masses. Metavolcanic Units Zat Zat - Altered tuffs: Very light-gray, light-greenish-gray to white, mottled red and yellow, hydrothermal ly altered rock interpreted to be silicified and/or sericitized tuffs. Unit occurs as map scale xenoliths within the East Farrington pluton. Zablt - Andesitic to basaltic lavas and tuffs: Typically unfoliated, green, gray-green, gray, dark gray and black; amygdaloidal, plagioclase porphyritic, amphibole/pyroxene porphyritic and aphanitic; andesitic to basaltic lavas and shallow intrusions. Hyaloclastic texture is common and imparts a fragmental texture similar to a lithic tuff on some outcrops. Tuffs associated with the lavas are weakly foliated to foliated, green to gray to silvery-gray, coarse tuff and lapilli tuff. Local homfels of unit present in the vicinity of Big Hole Road. Zfit-bw Zfit-bw -Felsic to intermediate tuffs of the Big Woods area: Heterogenous unit of felsic to intermediate composition tuffs and with lesser interlayers of andesitic to basaltic lavas and epiclastic rocks. Abundant dacitic lavas and tuffs, identical to Zdlt unit lithologies, are interlayered within unit. Ze/p Ze/p - Mixed epiclastic-pyroclastics: Green to Gray, conglomerates, conglomeratic sandstones, tuffaceous sandstones, and thinly layered siltstones. Unit contains lesser amounts of crystal and lapilli tuffs and minor andesitic to basaltic lavas and tuffs. Polymictic, matrix supported, conglomeratic sandstone to conglomerate containing subrounded to angular volcanic clasts is a distinctive lithology within the unit. Zdlt Zdlt - Dacitic lavas and tuffs: Distinctive dark-gray to black, siliceous, cryptocrystalline dacite, porphyritic dacite with plagioclase phenocrysts, and flow banded dacite. Tuffs associated with the lavas include welded and non-welded: greenish-gray to grayish-green, coarse plagioclase crystal tuff; lapilli tuff; lithic tuff. 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. 79° 07' 30" INDEX TO GEOLOGIC MAPPING ★ 0.25 0.125 0 0.25 0.5 0.75 1 UTM GRID AND 1999 MAGNETIC NORTH DECLINATION AT CENTER OF SHEET Stereonet - Contoured Poles to Foliation, Cleavage, Spaced Cleavage, and Shear Foliation ,N=145 Stereonet - Contoured Poles to Primary Layering. Bedding, Welding/Compaction Foliation, and Flow Banding in Carolina terrane rocks .N=35 Unidirectional Rose Diagram of Foliations, Cleavage, Spaced Cleavage, and Shear Foliations N=145 5— Г Unidirectional Rose Diagram of Primary Layering, Bedding, Welding/Compaction Foliation, and Flow Banding in Carolina terrane rocks N=35 Unidirectional Rose Diagram of Joints N=725 QAP plot of modal analyses from thin sections of East Farrington pluton samples. N S 1:24,000 SCALE CONTOUR INTERVAL 10 FEET Base topographic map is digital raster graphic image of the Farrington 7.5 minute USGS quadrangle (1994), North Carolina State Plane NAD 83 meters coordinate system Lambert Conformal Conic projection LOCATION OF THE FARRINGTON 7.5-MINUTE QUADRANGLE, NORTH CAROLINA Disclaimer: This Open-File report is preliminary and has not been reviewed for conformity with the North Carolina Geological Survey editorial standards or with the North American Stratigraphic Code. Further revisions or corrections to this preliminary map may occur prior to its release as a North Carolina Geological Survey map. Research supported by the U.S. Geological Survey, National Cooperative Geologic Mapping Program, under USGS award number 06HQAG0033. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government. 79° 00' CONTACTS Lithologic contacts - Distribution and concentration of structural symbols indicates degree of reliability. - geologic contact inferred geologic contact . concealed geologic contact - Quaternary alluvium contact l . iajor minor c . minor fault - D indicates downthrown side, U indicates upthrown side ? indicates extent uncertain inferred fold axis of major- and minor-scale syncline inferred fold axis of minor-scale anticline Zdlt-Q Zdlt-Q - Quartz dacite lavas and tuffs: Interlayered light-gray to white, unfoliated quartz and hornblende porphyritic dacite and foliated quartz crystal tuff. Quartz phenocrysts are distinctive with di-pyramidal form ranging from 1 mm up to 4 mm diameter. Hornblende phenocrysts are brown with a vitreous luster and are present up to 4 mm diameter. In hand sample, the groundmass is light-gray to white on weathered and fresh surfaces. Unfoliated varieties are interpreted to be lava or shallow intrusive bodies; foliated varieties are interpreted to be tuff. Quartz dacite porphyry unit of Eligman (1987). References: Clark, T.W., Gore, RJ.W., and Watson, M.E., 2001, Depositional and structural framework of the Deep River Triassic basin, North Carolina, in Hoffman, C.W., editor, Field trip guidebook, 50th Annual Meeting, Southeastern Section, Geological Society of America, Raleigh, North Carolina, April 2001, p. 27-50. Eligman, D„ 1987, Volcanic stratigraphy in the Carolina slate belt near Chapel Hill, North Carolina, unpublished M.S. thesis. University of North Carolina at Chapel Hill, 5 1 p. Fisher, R.V. and Schmincke, II. U., 1984, Pyroclastic rocks, Berlin, West Germany, Springer- Verlag, 472 p. Hauck, S.A., 1977, Geology and petrology of the northwest quarter of the Bynum quadrangle, Carolina slate belt. North Carolina, unpublished M.S. thesis, University of North Carolina at Chapel Hill, 146 p. Hoffman, C. W., and Gallagher, P. E., 1989, Geology of the Southeast Durham and Southwest Durham 7.5-minute quadrangles, North Carolina Geological Survey Bulletin 92, 34 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. STRUCTURAL SYMBOLS Observation sites are centered on the strike bar or are at the intersection point of multiple symbols. У strike and dip of primary bedding and layering у strike and dip of primary volcanic compaction and/or welding У strike and dip of primary volcanic flow banding X strike and dip of primary vertical volcanic flow banding У strike and dip of foliation X vertical foliation У strike and dip of cleavage / vertical cleavage 80 у strike and dip of shear foliation У strike and dip of diorite dike У strike and dip of joint У vertical joint * fault gouge V brittle fault plane 2У strike and dip of slickenside 12 У trend and plunge of slickenline lineation ® station location inactive quarry location 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. 33 1-335. 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. 17-21. Wagener, H.D., 1965, Areal modal variation in the Farrington igneous complex, Chatham and Orange Counties, North Carolina, Southeastern Geology, v. 6, no. 2, p. 49-77. Wagener, H.D., 1964, Areal modal variation in the Farrington igneous complex, Chatham and Orange counties, North Carolina, unpublished M.S. thesis, University of North Carolina at Chapel Hill, 5 1 p. Watson, M. E„ 1998, Geology of the Green Level 7.5-minute quadrangle, Chatham, Durham, and Wake Counties, North Carolina, North Carolina Geological Survey Open-File Report 98-3, 28 p. 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