Geologic map of the northwest portion of the Merry Oaks 7.5-minute quadrangle, Chatham and Lee Counties, North Carolina

DEPARTMENT OF ENVIRONMENT AND NATURAL RESOURCES DIVISION OF ENERGY, MINERAL, AND LAND RESOURCES TRACY E. DAVIS, DIRECTOR KENNETH B. TAYLOR, STATE GEOLOGIST This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program NORTH CAROLINA GEOLOGICAL SURVEY OPEN FILE REPORT 2012-02 79 07' 30 80 35° 45' 00" 71 MAP UNITS £ < z ш £ 3 о Qal alluvium (Qal) K/Tu post-Chalham Group undifferentiated sediments (K/Tu) о О N о w ш - T Jd / —U diabase Triassic Sedimentary Rocks Deep River Basin: Durham and Sanford Sub-basins Tree Trcs/si2 Trpc Trp conglomerate (Tree) of the Chatham Group and sandstone with interlayered siltstone of the Chatham Group Lithofacies Association II (Trcs/si2) conglomerate (Trpc) and interlayered sandstones, siltstones and mudstones of the Pekin Formation (Reinemund, 1955) о О О Ё о а. 0- о ш Metamorphic Rocks Нусо Formation metamorphosed volcaniclastic sedimentary and pyroclastic rocks associated with Hyco Formation: upper portion (stratigraphic relations uncertain) ca. 61 3 - 616 Ma (Wortman et al. , 2000; Bowman, 2010; and Bradley and Miller, 2011) Zhadlt (u) Zhdlt (u) Zhe/pl Zhablt mixed epiclastic-pyroclastic rocks with interlayered dacitic lavas (Zhe/pl) dacitic lavas and tuffs (Zhdlt (u)) andesitic to dacitic lavas and tuffs (Zhadlt (u)) andesitic to basaltic lavas and tuffs (Zhablt) \ Equal Area Schmidt Net Projection of Contoured Poles to Primary Layering, Bedding and Welding/Compaction Foliation of Carolina Terrane Rocks (squares) and of Bedding to Triassic Sediments (circles with cross) Contour Interval = 1 N = 54 Equal Area Schmidt Net Projection of Contoured Poles to Foliation and Cleavage Contour Interval = 1 N = 153 35 37' 30' 79° 00' 00" 35° 45' 00" 79 07' 30 35 37' 30" 79° 00' 00" Unidirectional Rose Diagram of Joints N = 429 Outer Circle = 7.5% Mean direction = 22 0.5 SCALE 1:24 000 0 Geology mapped between August 2011 and July 2012. 1 i Miles 8 34' 2010 Magnetic North Declination at Center of Sheet = 1,000 500 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 E3 Feet 0.5 1 j Kilometers MAP LOCATION INTRODUCTION Pre-Mesozoic crystalline rocks in the Merry Oaks Quadrangle are part of the Virgilina sequence of the Neoproterozoic to Cambrian Carolina terrane of the Carolina Zone (Harris and Glover. 1988; Hibbard et al., 2002; and Hibbard et al.. 2006). In the region of the map area, the Virgilina sequence can be separated into two lithotectonic units: 1) the Hyco Formation and 2) the Aaron Formation. The Hyco Formation consists of ca. 615 to 633 Ma (Wortman et al., 2000; Bowman, 2010; Bradley and Miller, 2011) metamorphosed layered volcaniclastic rocks and plutonic rocks. Available age dates (Wortman et al., 2000; Bradley and Miller. 2011) indicate the Hyco Formation may be divided into lower (ca. 630 Ma) and upper (ca. 615 Ma) members (informal) with an apparent intervening hiatus of magmatism. In northeastern Chatham County. Hyco Formation units are intruded by the ca. 579 Ma (Tadlock and Loewy, 2006) East Farrington pluton and associated West Farrington pluton. The Aaron Formation (not present in the map area) consists of metamorphosed layered volcaniclastic rocks with youngest detrital zircons of ca. 578 and 588 Ma (Samson et al., 2001 and Pollock. 2007. respectively). The Virgilina sequence was folded and subjected to low grade metamorphism during the ca. 578 to 554 Ma (Pollock, 2007) Virgilina deformation (Glover and Sinha, 1973; Harris and Glover, 1985; Harris and Glover, 1988; and Hibbard and Samson. 1995). In the map area, original layering of Virgilina sequence lithologies are interpreted to range from shallowly to steeply dipping due to open to isoclinal folds that are locally overturned to the southeast. Map units of meta-volcaniclastic rocks include various lithologies that when grouped together are interpreted to indicate general environments of deposition (or lithofacies). The dacitic lavas and tuffs unit is interpreted to represent dacitic domes and proximal pyroclastics. The andesitic to basaltic lavas and tuffs unit is interpreted to represent eruption of intermediate to mafic lava flows and associated pyroclastic deposits. The epiclastic/pyroclastic units are interpreted to represent deposition from the erosion of dormant and active volcanic highlands. Meta-volcaniclastic units within the map area display lithologic relationships similar to units present in northern Orange and Durham Counties. Due to these similarities, the meta-volcaniclastic units have been tentatively assigned to the upper portions of the Hyco Formation; geochronologic data is needed to confirm this interpretation. The eastern portion of the Chatham County is underlain by Triassic-aged sedimentary rocks of the Deep River Mesozoic basin which is separated into three sub-basins (Durham. Sanford and Wadesboro). The Colon cross structure (Reinemund. 1955), located immediate southwest of the Merry Oaks Quadrangle, is a constriction zone in the basin characterized by crystalline rocks overprinted by complex brittle faulting. The Colon cross-structure marks the transition between the Durham and Sanford sub-basins. The Merry Oaks Quadrangle contains rock associated with both the Chatham Group of the Durham sub-basin and the Pekin Formation of the Sanford sub-basin. Dikes of Jurassic aged diabase intrude the Triassic sediments. Diabase dikes also intrude the crystalline rocks of the map area. Quaternary aged alluvium is present in most major drainages. All pre-Mesozoic rocks in the map area 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. Jurassic diabase dikes are un metamorphosed. The nomenclature of the International Union of Geological Sciences subcommission on igneous and volcanic rocks (IUGS) after Le Maitre (2002) 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 within the adjacent areas (Eligman. 1987 and Wagener. 1964 and 1965) have used various nomenclature systems for the igneous rocks. The raw data, when available, 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). DESCRIPTION OF MAP UNITS SEDIMENTARY UNITS Qal K/Tu Tree Trcs/si2 Trpc Trp Jd / / Zhe/pl Zhdlt (u) Zhadlt (u) Zhablt 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. 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 mainly exposed on shores of B. Everett Jordan Lake. Unit is in unconformable contact with Triassic sediments. Tree - Conglomerate of the Chatham Group Lithofacies Association III: Reddish-brown to dark brown, irregularly bedded, poorly sorted, cobble to boulder conglomerate. Clasts are chiefly miscellaneous felsic and intermediate metavolcanic rocks and quartz. Typically present adjacent to border faults. Trcs/si2 - Sandstone with interbedded siltstone of the Chatham Group Lithofacies Association II: Grayish-pink to pale-red, micaeous (typically white mica), coarse- to very coarse-grained, pebbly, cross-bedded lithic arkose interbedded with maroon, micaeous mudstone, burrowed and rooted siltstone. Bioturbation is usually surrounded by greenish-blue to gray reduction halos. Good outcrops typically exhibit cyclical fining upward depositional sequences. These rocks are assigned to the Lithofacies Association II of Hoffman and Gallagher, 1991 and Watson. 1998. This unit has been extended into the Merry Oaks Quadrangle to edge-match with the Farrington Quadrangle geologic map (Bradley et al., 2007) and the New Hill geologic map (Clark et al., 2004) .The clastic rocks of Lithofacies Association II are interpreted to have been deposited in a meandering stream fluvial system. Trpc - Conglomerate of the Pekin Formation: Reddish-brown to dark brown to purplish-red, irregularly bedded, poorly sorted, cobble to boulder conglomerate. Clasts are chiefly miscellaneous felsic and intermediate metavolcanic rocks and quartz. Typically present adjacent to border faults. Outcrops and boulders of float identified as part of Pekin Formation are strongly indurated compared to conglomerates identified as part of Chatham Group. Identified as the Pekin Formation-basal conglomerate by Reinemund (1955). Trp - Pekin Formation: Gray. Brown to maroon, white mica bearing, interbedded mudstones, siltstones and arkosic sandstones. Outcrops and boulders of float identified as part of Pekin Formation are strongly indurated compared to conglomerates identified as part of Chatham Group. Identified as the Pekin Formation by Reinemund (1955). INTRUSIVE AND METAINTRUSIVE 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 spheriodally weathered boulders with a grayish-brown weathering rind. Red station location indicates outcrop or boulders of diabase. METAVOLCANIC UNITS HYCO FORMATION - UPPER PORTION (STRATIGRAPHIC ORDER UNCERTAIN) Zhe/pl - Mixed epiclastic-pyroclastic rocks with interlayered dacitic lavas: Grayish-green to greenish-gray, locally with distinctive reddish-gray or maroon to lavender coloration; metamorphosed: conglomerate, conglomeratic sandstone, sandstone, siltstone and mudstone. Lithologies are locally bedded; locally tuffaceous with a cryptocrystalline-like groundmass. Siltstones are locally phyllitic. Locally contain interbedded dacitic lavas identical to Zhdlt unit. Contains lesser amounts of fine- to coarse tuff and lapilli tuff with a cryptocrystalline-like groundmass. Minor andesitic to basaltic lavas and tuffs present. Silicified and/or sericitized altered rock similar to Zhat unit are locally present. Conglomerates and conglomeratic sandstones typically contain subrounded to angular clasts of dacite in a clastic matrix. Portions of the Zhe/pl unit are interpreted to have been deposited proximal to active volcanic centers represented by the Zhdlt unit but are also interpreted to record the erosion of proximal volcanic centers after cessation of active volcanism. Zhdlt (u) - Dacitic lavas and tuffs of the upper portion of the Hyco Formation: Greenish-gray to dark gray, siliceous, aphanitic dacite, porphyritic dacite with plagioclase phenocrysts. and flow banded dacite. Dacite with hyaloclastic textures are common. Welded and non-welded tuffs associated with the lavas include: greenish-gray to grayish -green, fine tuff, coarse plagioclase crystal tuff and lapilli tuff. Locally, interlayers of immature conglomerate and conglomeratic sandstone with abundant dacite clasts are present. The dacites are interpreted to have been coherent extrusives or very shallow intrusions associated with dome formation. The tuffs are interpreted as episodic pyroclastic flow deposits, air fall tuffs or reworked tuff's generated during formation of dacite domes. The unit occurs as map scale pods surrounded by clastic rocks of Zhe/pl unit. Wortman et al. (2000) reports an age of 6 15.7+3.7/- 1 .9 Ma U-Pb zircon date for a dacitic tuff from the unit in the Rougemont quadrangle. Zhadlf (u) - Andesitic to dacitic lavas and tuffs of the upper portion of the Hyco Formation: Black to dark gray, gray-green to green; aphanitic andesite to dacite and porphyritic andesite to dacite with plagioclase phenocrysts. Hyaloclastic textures are common, lnterlayed with the lavas are gray to black; welded and non-welded; coarse tuff, lapilli tuff, and tuff breccia. Rocks interpreted as andesites have distinct interior weathering rind of light brown to gray and fresh surfaces exhibit non-vitric like textures in contrast to dacites. Zhablt - Andesitic to basaltic lavas and tuffs: Green, gray-green, gray, dark gray and black; typically unfoliated, 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. Locally interlayered with meta-sediments identical to the Zhe/pl unit. REFERENCES: Bowman. J.D., 2010.. The Aaron Formation: Evidence for a New Lithotectonic Unit in Carolina. North Central North Carolina, unpublished masters thesis. North Carolina State University. Raleigh. North Carolina. 1 16 p. Bradley, P.J.. Gay, N.K., Bechtel, R. and Clark. T.W.. 2007, Geologic map of the Farrington 7.5-minute quadrangle. Chatham, Orange and Durham Counties, North Carolina: North Carolina Geological Survey Open-file Report 2007-03, scale 1 :24.000, in color. Bradley, P.J. and Miller, В. V, 2011. New geologic mapping and age constraints in the Hyco Arc of the Carolina terrane in Orange County. North Carolina: Geological Society of America Abstracts with Programs. Vol. 43. No. 2. Clark. T.W., Blake, D.E., Stoddard. E.F., Carpenter, P.A., HI. and Carpenter, R.H., 2004. Preliminary bedrock geologic map of the Raleigh 30’ x 60’ quadrangle. North Carolina: North Carolina Geological Survey Open-file Report 2004-02. scale 1 : 100.000. in color. Eligman. D.. 1987, Volcanic stratigraphy in the Carolina slate belt near Chapel Hill. North Carolina, unpublished masters thesis. University of North Carolina at Chapel Hill. 51 p. Fisher, R.V. and Schmincke H.-U., 1984, Pyroclastic rocks. Berlin. West Germany, Springer- Verlag, 472 p. Glover, L., and Sinha. A., 1973, The Virgilina deformation, a late Precambrian to Early Cambrian (?) orogenic event in the central Piedmont of Virginia and North Carolina. American Journal of Science, Cooper v. 273-A. pp. 234-251 . Harris, C.. and Glover, L.. 1985, The Virgilina deformation: implications of stratigraphic correlation in the Carolina slate belt, Carolina Geological Society field trip guidebook. 36 p. Harris, C.. and Glover. 1 988, 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. Hibbard. J., Samson. S., 1 995. Orogenesis exotic to the Iapetan cycle in the southern Appalachians. In. Hibbard. J., van Staal, C., Cawood. P. editors. Current Perspectives in the Appalachian- Caledonian Orogen. Geological Association of Canada Special Paper, v. 41. pp. 191-205. Hibbard. J., Stoddard. E.F., Secor. D., Jr., and Dennis. A.. 2002, The Carolina Zone: Overview of Neoproterozoic to early Paleozoic peri-Gondwanan terranes along the eastern flank of the southern Appalachians: Earth Science Reviews, v. 57. n. 3/4. p. 299-339. Hibbard. J. P., van Staal. C. R., Rankin, D. W., and Williams, H.. 2006, Lithotectonic map of the Appalachian Orogen, Canada-United States of America, Geological Survey of Canada, Map-2096A. 1:1. 500.000-scale. Hoffman. C. W.. and Gallagher. P. E., 1989. Geology of the Southeast Durham and Southwest Durham 7.5-minute quadrangles. North Carolina Geological Surv ey Bulletin 92. 34 p. Le Maitre. R.W., Ed., 2002. Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences (IUGS) Subcommission on the Systematics of Igneous Rocks: Cambridge, Cambridge University Press. 252 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. 1 94 p. Reinemund. J.A.. 1955, Geology of the Deep River coal field. North Carolina: U.S. Geol. Survey Prof. Paper 246. 159 p. Samson. S.D. and Secor. D.. 2001. Wandering Carolina: Tracking exotic terranes with detrital Zircons, GSA Abstracts with Programs Vol. 33, No. 6, p. A-263 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.. 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. 51 p. 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. 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. 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. 1 08, pp. 321-338. CONTACTS, FOLDS AND OTHER FEATURES Lithologic contacts - Distribution and concentration of structural symbols indicates degree of reliability. - fV - - ft - - contact - location known - contact - location inferred . contact - location concealed - Qal contact - brittle fault - inferred ^ ^ Bonsai - Morrisville Fault (approximate location) _ A ' cross section line iiiii mu mu inn mu inn inn uni n fold axis - overturned anticline - inferred fold axis - overturned syncline - inferred gradational contact diabase contact - dashed where inferred, dotted where concealed in cross section, fold form lines in cross section, inferred axial trace of large-scale fold V 22 34 74 У 60 У го cross section scale - 1:24 000 no vertical exaggeration У у strike and dip of inclined primary bedding and layering strike and dip of inclined primary bedding and layering (multiple observations at one locality) strike and dip of primary flow banding strike and dip of primary volcanic compaction and/or welding foliation strike and dip of inclined regional foliation strike and dip of inclined regional foliation (multiple observations at one locality) strike of vertical regional foliation strike of vertical regional foliation (multiple observations at one locality) diabase station location abandoned quarry 7У 65 76 V 74 У °yy У у V У © 70 strike and dip of cleavage strike and dip of cleavage (multiple observations at one locality) Strike and dip of cataclastic cleavage interpreted as a result of brittle deformation Strike and dip of cataclastic cleavage interpreted as a result of brittle deformation (multiple observations at one locality) Fault plane - normal strike and dip of inclined joint surface strike and dip of inclined joint surface (multiple observations at one locality) strike of vertical joint surface strike of vertical joint surface (multiple observations at one locality) strike and dip of quartz vein bearing and plunge of slickenline station location USGS gauging station (part of base map features) GEOLOGIC MAP OF THE NORTHWEST PORTION OF THE MERRY OAKS 7.5-MINUTE QUADRANGLE, CHATHAM AND LEE COUNTIES, NORTH CAROLINA By Philip J. Bradley, Heather D. Hanna and Michael J. Malaska by foot by car Digital representation by Michael A. Medina and Philip J. Bradley 2012 Base map is from USGS 2010 GeoPDF of the Merry Oaks 7.5-minute quadrangle. Aerial photo, map collar and select features removed. Bounds of GeoPDF based on 7.5-minute grid projection in UTM 17S; North American Datum of 1983 (NAD83). This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program, award number G1 1 AC20296. 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. Disclaimer: This Open-File report is preliminary and has been reviewed for conformity with the North Carolina Geological Survey editorial standards or with the North American Stratigraphic Code. 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