- Title
- Geologic map of the Chapel Hill 7.5-minute quadrangle, Orange and Durham Counties, North Carolina
-
-
- Date
- 2008
-
-
- Creator
- ["Bradley, Philip J. (Philip Julian), 1968-"]
-
- Place
- ["Chapel Hill, Orange County, North Carolina, United States","Durham County, North Carolina, United States"]
-
- Series
- Open file report (North Carolina. Geological Survey Section) ; 2004-01.
-
-
Geologic map of the Chapel Hill 7.5-minute quadrangle, Orange and Durham Counties, North Carolina
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GEOLOGIC MAP OF THE CHAPEL HILL 7.5-MINUTE QUADRANGLE, ORANGE AND DURHAM COUNTIES, NORTH CAROLINA
This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program
DEPARTMENT OF ENVIRONMENT AND NATURAL RESOURCES
DIVISION OF LAND RESOURCES
JAMES D. SIMONS, STATE GEOLOGIST
NORTH CAROLINA GEOLOGICAL SURVEY
OPEN FILE REPORT 2004-01 Revision-02 (2008)
BY PHILIP J. BRADLEY, CINDY M. PHILLIPS,
NORMAN K. GAY, AND STEPHEN J. FUEMMELER
Digital representation by Michael A. Medina and Philip J. Bradley
2004
EXPLANATION
Zablt
Zdirgb
Zablt
Trcs/si1
Zablt
llietns-
Ci
-076
CH-2124
CONTACTS
Lithologic contacts - Distribution and concentration
of structural symbols indicates degree of reliability.
Contact dashed where inferred.
Contact dotted where concealed.
FAULTS
u
""" d" "
Faults- Dashed where inferred, dotted where concealed.
U indicates upthrown block, D indicates downthrown block.
STRUCTURAL SYMBOLS
Observation sites arc centered on the strike bar or arc
31 strike and dip of primary
^ bedding and layering
37 , strike and dip of primary volcanic
^ compaction and/or welding
My strike and dip of foliation
V strike and dip of foliation S2
strike and dip of cleavage
the intersection point of multiple symbols.
X vertical bedding and layering
X vertical welding or compaction foliation
X vertical foliation
X vertical foliation S2
X* vertical cleavage
&
ft
FOLDS
Interpreted fold hinge of large
scale anticline. Arrow indicates
direction of plunge.
Interpreted fold hinge of large
scale syncline. Arrow indicates
direction of plunge.
1
My strike and dip of shear foliation
strike and dip of joint
strike and dip of quartz vein
strike and dip of slickenside
72 strike and dip of
slaty cleavage
21
X vertical shear foliation
X vertical joint
X vertical quartz vein
3y strike and dip of fault plane
X dike trend
13
N
S
0.25 0 0.25 0.5 0.75 1 Miles
1,250
0
1,250
2,500
3,750
5,000 Feet
375
0
375
750
1,125
1,500 Meters
1 :24,000 SCALE
CONTOUR INTERVAL 10 FEET
All pre-Mesozoic rocks of the Chapel Hill quadrangle have been metamorphosed to at least the chlorite zone of the
greenschist metamorphic facies. Many of the rocks also display weak to 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 1 979) 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 Chapel Hill quadrangle (Allen and Wilson, 1968; Black, 1977; Bland, 1972;
Butler, 1963 and 1964; Chiulli, 1987; Clark, 1957; Hayes, 1962; Kirstein, 1956; Mann et al., 1965;and Wagener, 1964 and 1965)
have used various nomenclature systems for the igneous rocks. The raw data of some 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). A review of the area geology is provided in Bradley et al., 2006.
SEDIMENTARY UNITS
Qal Alluvium: Unconsolidated clay, silt, sand and gravel to cobble-sized clasts, subrounded to angular, deposited in
drainages.
Qcv - Quaternary colluvium: Accumulations of angular cobbles and boulders of unit Zdlt on the north slope of
McCauley Mountain. Possibly formed by Quaternary slope movements (rock slide, rockfall, etc.).
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. Distribution of unit in Chapel Hill quadrangle interpreted from
edge matching with geologic maps of Green Level (Watson, 1998) and Farrington quadrangles (Bradley et al., 2007) and
interpretation from topography.
Trcs/sil - Sandstone with interlayered siltstone of the Chatham Group Lithofacies Association I: Grayish-pink, pinkish-gray,
and light-gray; fine- to coarse-grained, micaeous, slightly clayey, moderately poor to moderately well sorted, subangular to
subrounded arkose and lithic arkose; dark red to reddish-brown, very silty, micaeous, moderately well sorted, fine-grained
sandstone; and dark red to reddish-brown, 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 1
of Hoffman and Gallagher, 1989 and Watson, 1998. The clastic rocks of Lithofacies Association I are interpreted to have been
deposited in a braided stream fluvial system.
INTRUSIVE AND META-INTRUSIVE UNITS
Jd Diabase: Black to greenish-black, fine- to medium-grained, dense, consists primarily of plagioclase, augite, and olivine.
Commonly occurs as dikes up to 100 ft wide. Present as both dikes and sills in map area. Diabase typically occurs as
spheriodally weathered boulders with a grayish-brown weathering rind. Red station location indicates outcrop or boulders
of diabase.
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, <1 mm in diameter, with euhedral terminating
crystals are common in some specimens. 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. U-Pb zircon geochronologic data (Tadlock and Loewy, 2006) indicate that the East Farrington pluton is ca. 579 Ma.
Zgr Granite: Typically massive, fine- to medium-grained with dark green amphiboles (commonly rimmed by epidote and
chlorite) and
+/-
biotite. Light-pink to pink, alkali feldspars are prominent and give the rock a pinkish hue. Orange-pink to
grayish-orange pink, fine-grained aplite with a sub-graphitic texture is present in dikes ranging from centimeters to meters in
width. Rocks of granitic composition occur primarily within the informally named Chapel Hill pluton. Granite of the Chapel
Hill pluton has an interpreted U-Pb zircon crystallization age of 633
+2/-
1.5 Ma (Wortman et al., 2000). An unpublished U-Pb
zircon age of 63 1 .6
+/-
7.9 Ma was also reported by Mehlop (1994) for the Chapel Hill pluton.
Zgd - Granodiorite: Leucoractic to mesocratic, fine- to medium-grained, equigranular to porphyritic granodiorite. In the
northern portion of the quadrangle, the granodiorite is mainly pinkish hued, fine- to medium-grained with dark green to
black <1 mm to 4 mm clots of mafic minerals interpreted to be biotite and amphibole masses. Chlorite growth on biotite
and amphibole is present. Medium-grained, with light pink to pinkish white alkali feldspars (up to 5 mm diameter), porphyritic
granodiorite is intermingled in the northern portion of the quadrangle. In the central and southern portions of the quadrangle the
granodiorite is mainly whitish-gray, fine- to medium-grained, biotite,
+/-
hornblende granodiorite with minor pink-colored alkali
feldspar. Plagioclase grains are often sericitized and saussuritized and exhibit a greenish color throughout the unit.
Zdi - Diorite: Mainly greenish-gray to gray, mesocratic, medium-grained, equigranular diorite. Major minerals include
plagioclase and hornblende. Greenish-white plagioclase crystals compose up to 50% of the rock and are typically sericitized
and saussuritized. Individual stocks contain varying amounts of tonalite and quartz diorite. Hornblende is typically altered
to chlorite and actinolite masses. Weathered cobbles and boulders typically display a “bleached" weathering rind of white
to grayish-white.
Zdi-fine Fine-grained diorite: Green, fine-grained diorite. The rock is green in hand sample from saussuritization of
plagioclase.
Zqmd - Quartz monzodiorite: Greenish-gray to gray, mesocratic, medium-grained, equigranular quartz monzodiorite.
Major minerals include plagioclase and hornblende. In field, rock is indistinguishable from typical diorite except for rare
pinkish alkali feldspar in some samples (specifically on the south side of Blackwood Mountain). Rock type designation
based on recalculated whole rock chemical analyses of Bland, 1972.
Zt-qdi - Tonalite to quartz diorite: Light-gray, fine to medium-grained, hornblende tonalite to quartz diorite. Visible quartz
content ranges from 5% up to 20%. Outcrops of this unit are typically finer-grained, lighter in color, and have visible quartz
in comparison to typical medium-grained diorite.
Zdi-gb - Diorite to Gabbro: Lesser greenish-gray to gray, medium-grained, equigranular, hornblende diorite intermingled with
greater amounts of dark-gray to greenish-gray, medium-grained gabbro with pyroxene. Plagioclase crystals are typically
saussuritized and exhibit a greenish color. Outcrops with heavily saussuritized plagioclase have a high Color Index causing
difficulty in distinguishing between gabbro and diorite in the field.
Zgb Gabbro: Dark-gray to greenish-gray, mesocratic to melanocratic, medium-grained gabbro. Major minerals include
plagioclase and augite. In outcrop, the diorites and gabbros are very similar in appearance and are difficult to distinguish from
each other. According to Mann, et al (1965), the plagioclase crystals are zoned with cores of An53 and
ЛпЗ
1 at the margins.
Augite grains (present up to 3 mm) are fringed with uralite and are sometimes replaced by hornblende, chlorite, or magnetite.
The map pattern of gabbro within the Meadow Flats pluton was drawn incorporating the Bland (1972) whole rock data with
field data from this study.
Zum - ultramafic: Black, coarse-grained (5 mm to 10 mm), ultramafic rock consisting mainly of poikilitic crystals of relict
brown hornblende that are partially replaced by actinolite and chlorite. Other minerals include serpentine, talc, chlorite,
actinolite, and opaque minerals. Minor relict orthopyroxene is present. Hayes (1962) interpreted the protoliths as olivine-rich
wehrlite (with approximately 50% olivine) and clinopyroxenite. Bulter (1989) interpreted the body to be an intrusion of a
crystal mush formed by differentiation of gabbroic magma at depth. Normalized whole rock analysis from a sample collected
east of Iron Mine Hill (CH-2027) plots within the olivine-clinopyroxenite field on an Ol/Opx/Cpx ternary diagram.
METAVOLCANIC UNITS
Zq - Laurel Hill quartz body: Aresistant topographic feature of milky white quartz. Allen and Wilson (1968) described the
Laurel Hill quartz body as being composed of a cluster of quartz veins 600 feet in length and 90 feet in width. Float boulders
and cobbles of quartz are present over an area of over 300 feet wide.
Zat - Altered tuffs: Very light gray to light greenish gray (whitish in areas) with red and yellow mottling. Alteration consists
of silicified and pyrophyllitized rock. Sericite phyllite, pods of pyrophyllite, and quartz + phyrophyllite rock all with <1 mm
to 2 mm diameter weathered sulfides are common. Fine-grained chloritoid porphyroblasts (<1 mm) are present in some
pyrophyllite bearing rocks. Relict lithic clasts and kaolinitized feldspar crystal shards are visible in some exposures. Relict
structures are obliterated in heavily altered rocks. Map area contains boulders (up to several feet in diameter) and outcrop of
massive milky quartz and quartz + sericite rock.
Ze Epiclastics: Mixed unit of metasedimentary rocks. Includes mudstone, siltstone, sandy siltstone, sandstone, conglomeratic
sandstone, and conglomerate. Minor interlayers of fine tuff" to vitric tuff are present. Mudstones and siltstones are sometimes
phyllitic or silicified, greenish-gray to gray, with continuous, parallel to slightly wavy, thin lamina to very thin beds, occasionally
with small-scale loading structures. The mudstones and siltstones are composed of quartz, sericite, and traces of a black detrital
heavy minerals (<1 mm in diameter). Siltstones are typically interbedded with the sandstones. Sandstones are dark-gray, gray,
greenish-gray, grayish-green, litharenites and feldspathic litharenites composed of volcanic rock fragments, feldspar, quartz, and
rare intrusive rock fragments. Conglomerates include matrix supported and clast supported polymictic conglomerate composed
of angular to rounded pebble to gravel-size sediment. Sandstone and conglomerate beds often fill scour channels in the siltstones.
Ze-m 1 and Ze-m2 Morgan Creek epiclastics: Contains well bedded, greenish-gray to gray, siltstone, sandy siltstone, sandstone,
conglomeratic sandstone, and conglomerate. The unit was divided into two lithofacies, Ze-ml and Ze-m2: Zmel is exposed
mainly along Morgan Creek; it is mostly well bedded siltstones with lesser sandstone and conglomerate beds; Ze-m2, occurs to
the south and southwest of Ze-ml and is overall coarser, containing mostly sandstones and conglomerates with lesser well bedded
siltstones. Siltstones range from thinly laminated to very thinly bedded (<1 mm to 1 0 mm) with individual beds that can be traced
continuously in the outcrops. Sandstone and conglomerate beds often fill scour channels in the siltstones. The conglomerates range
from matrix-supported to clast-supported, contain subrounded to rounded lithic clasts of porphyritic dacite, aphanitic volcanic rock,
and granitoid in a silt to sand matrix. Individual beds are typically graded from sand-size to silt-size with abrupt upper surfaces.
Ze/p
Ze/p - 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 coarse tuff and
lapilli tuff. Abundant silicified and/or sericitized altered rock similar to Zat unit is present near contacts with plutonic rocks.
Ze/p-n
Ze/p -n - Mixed epiclastic-pyroclastic rocks of Neville Creek area: Heterogeneous unit of felsic to intermediate composition
tuffs and lavas, tuffaceous sandstones and conglomeratic sandstones.
Zft
Zft - Felsic tuffs: Greenish-gray, silvery-gray, and gray, massive to foliated, lithic, lithic-crystal, crystal, ash, and minor
welded tuffs. Layering ranges from massive to thinly bedded (3 cm to 10 cm).
Zft-b
Zft-b Felsic tuffs of the Blackwood area: Green-gray to gray coarse tuff and lapilli tuff. Plagioclase crystals and crystal
fragments are common. Lithic clast types includes dark-gray to black; magnetic; 1 to 70 mm; cryptocrystalline lava, or
clasts of porphyritic lava with feldspar phenocrysts. Porphyritic clasts are identical to the porphyritic phases of unit Zdlt.
Outcrops and thin sections show a prominent welding and/or compaction foliation with fiamme-shaped clasts. Outcrops
typically occur as very resistant fin-like outcrops.
Zdlt
Zdlt - Dacitic lavas and tuffs: Distinctive dark-gray to black, siliceous, cryptocrystalline dacite, porphyritic dacite with
plagioclase +- quartz phenocrysts, and flow banded dacite. (A distinct quartz + plagioclase porphyritic dacite is present
at Bald Mountain.) 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. A sample, identified as a flow-banded rhyolite,
collected from a location immediately west of University Lake, yielded an upper intercept date from single zircons of
632.9
+2.6/-
1 .9 Ma (Wortman et al. 2000).
Zablt
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.
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, 58p.
Black, W.W, 1977, The geochronology and geochemistry of the Carolina Slate belt of north-central North Carolina, Ph.D. thesis,
University of North Carolina, Chapel Hill, 1 1 8p.
Bland, A.E., 1972, Geochemistry of the Meadow Flats Complex, Orange County, North Carolina, M.S. thesis. University of
North Carolina at Chapel Hill, 49p.
Bradley, R J., Gay, N.K., Clark, T. W, 2006, An overview of new geologic mapping of the Chapel Hill, Hillsborough and Efland 7.5-minute
quadrangles. Orange and Durham Counties, Carolina terrane. North Carolina, 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. 1-16.
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.
Butler, J.R., 1963, Rocks of the Carolina slate belt in Orange County, North Carolina, Southeastern Geology, v.4, p. 167-185.
Butler, J.R., 1964, Chemical analyses of rocks of the Carolina Slate belt, Southeastern Geology, v. 5, p. 101-1 12.
Butler, J.R., 1989, Review and classification of ultramafic bodies in the Piedmont of the Carolinas, p. 19-31, in Mittwede, S.K. and
Stoddard, E.F., editors, Ultramafic Rocks of the Appalachian Piedmont, Geological Society of America Special Paper 231, 103p.
Chiulli, A.T., 1987, The geology and stratigraphy of the northeast portion of White Cross quadrangle. Orange County, North
Carolina, M.S. thesis, University of North Carolina at Chapel Hill, 70p.
Clark, T.G., 1957, Geology of the crystalline rocks in the southern half of the Chapel Hill, North Carolina quadrangle, M.S.
thesis, University of North Carolina at Chapel Hill, 56p.
Fisher, R.V. and Schmincke II. -U., 1984, Pyroclastic rocks, Berlin, West Germany, Springer- Verlag, 472 P.
Harris, C, and Glover, 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.
Hayes, L.D., 1962, A petrographic study of the crystalline rocks of the Chapel Hill, North Carolina quadrangle, M.S. thesis,
University of North Carolina at Chapel Hill, 67p.
Hoffman, C.W. and Gallagher, P, 1989, Geology of the Southeast Durham and Southwest Durham 7.5-minute quadrangles,
North Carolina, Bulletin 92, North Carolina Geological Survey, 34p.
Kirstein, D.S., 1956, The geology of the crystalline rocks of the northern half of the Chapel Hill, North Carolina quadrangle,
M.S. thesis, University of North Carolina at Chapel Hill, 26p.
Mann, V.I., Clark, T.G., Hayes, L.D., and Kirstein, D.S., 1965, Geology of the Chapel Hill Quadrangle, North Carolina, North
Carolina Division of Mineral Resources Special Publication 1 , 35 p.
Mehlhop, A., 1 994, U-Pb age for the Chapel Hill pluton Implications for the Carolina slate belt history, unpublished senior thesis,
University of North Carolina, Chapel Hill, 13 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 systematics 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., 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.
Wagener, II. 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. 108, p. 321-338.
Schematic representation of stratigraphic relationships of
geologic units in the Chapel Hill 7.5-minute quadrangle.
Stereonet - Contoured Poles
of Foliation and Cleavage
N=173
Unidirectional Rose Diagram
of Foliation and Cleavage
N=173
Stereonet - Contoured Poles
Unidirectional Rose Diagram
Unidirectional Rose Diagram
of primary layering and bedding
of primary layering and bedding
of Joints
N=29
N=29
N=519
И
Mines, Prospects, and Pits
1 - Duke Forest Prospect
2 - Weaver-Carr Prospect
3 - Nunn Mountain Mine
4 - Laurel Hill Quartz Prospect
5 - Iron Mine
6 - Gravel Pits
/
trend and plunge of slickenline
16 trend and plunge of
^ crenulation lineation
® station location
72
shear zone
CH-757
80
' trend and plunge of lineation
19
' trend and plunge of fold axis
»
Jd - boulder location or outcrop
У
fault gouge
Base topographic map is digital raster graphic image
of the Chapel Hill 7.5-minute USGS quadrangle (l 993),
North Carolina State Plane NAD 83 meters coordinate system.
Meadow Flats
□ Rock sample collected for geochemical analysis
N
0
New Hope Creek
Approximate location of geochronologic sample
of Wortman et al. (2000)
1“ 08'
20 MILS
UTM GRID AND 2004 MAGNETIC NORTH
DECLINATION AT CENTER OF SHEET
DISTRIBUTION OF PRE-MESOZOIC
PLUTONIC ROCKS AND
INFORMAL PLUTON NAMES
SE
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Plutons
Kirstein (1956), Clark (1957), Hayes (1962), Wagener (1965), and Mann, et. al. (1965) described the intrusive rocks of
the Chapel Hill quadrangle in detail. Black (1977) grouped the intrusive rocks of the Chapel Hill area into lour plutons:
1) Meadow Flats pluton, 2) Duke Forest pluton, 3) Chapel Hill pluton, and 4) East Farrington pluton.
Meadow Flats pluton
The informally named Meadow Flats pluton, located in the area of the Meadow Flats lowland in the northwest portion of the
quadrangle, was originally mapped by Kirstein (1956) and later studied in detail by Bland (1972). The Meadow Flats pluton
has been described as a composite pluton of gabbro, diorite, and granodiorite based on the nomenclature used by Kirstein
(1965). Whole rock chemical analyses from 57 rock samples collected throughout the Meadow Flats pluton by Bland
(1972) were normalized and plotted on QAP diagrams for this study. According to IUGS nomenclature, the rocks previously
categorized as granodiorite plot as quartz monzodiorite. In the field, these rocks are similar in appearance to the diorites.
The areas previously mapped as granodiorite are designated as quartz monzodiorite in this study.
Duke Forest pluton
The informally named Duke Forest pluton (Black, 1977), is located in the northeast portion of the quadrangle on land partially
owned by Duke University. The pluton is composed of diorite with a small amount of gabbro on the east and granodiorite on
the west. Cole (1971, unpublished report) produced a geologic map of the area in the vicinity of the Duke Forest pluton based
on a determination of rock type from point-count analyses from thin sections. The boundary between the Duke Forest pluton
and the Chapel Hill pluton is not distinct and the rocks assigned to the plutons appear to grade into one another. The last
appearance of a porphyritic granodiorite, generally restricted to the northern portion of the quadrangle, north of Eastwood
Lake, has been arbitrarily selected as the boundary between the Duke Forest pluton and Chapel Hill pluton.
Chapel Hill pluton
The Chapel Hill pluton is composed primarily of granite and granodiorite with several stocks of diorite to the west and
northwest. The Chapel Hill pluton underlies UNC campus and the town of Chapel Hill and is bounded on the east by
Triassic sediments. Three horsts, one composed of granitic rock and the other two composed of diorite, are present
within the Triassic basin.
East Farrington pluton
Rocks assigned to the East Farrington pluton outcrop within the southern portion of the quadrangle. The majority of the East
Farrington pluton is located within the Farrington and Bynum quadrangles. Separated from the Chapel Hill pluton by a thin
strip of volcaniclastic and volcanosedimentary rocks less than one mile wide, the East Farrington is primarily a granite with
minor amounts of granodiorite and diorite.
O’
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.
LOCATION OF THE CHAPEL HILL 7.5-MINUTE
QUADRANGLE, NORTH CAROLINA
— -2000’
Research supported by the U.S. Geological Survey, National Cooperative
Geologic Mapping Program, under USGS award number 03HQAG0170.
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.
NCGS OPEN FILE REPORT 2004-01 Revision - 02 (2008)
GEOLOGIC MAP OF THE CHAPEL HILL 7.5-MINUTE QUADRANGLE, ORANGE AND DURHAM COUNTIES, NORTH CAROLINA
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