1. THE GEOLOGY OF ROWAN COUNTY, CENTRAL CAROLINA TERRANE , N.C
PRIVETT, Donald R., President, S.T.A.R. Environmental, 1 Circle Street, Great
Falls, S.C. 29055, drprivett@gmail.com
Rowan County in central North Carolina Piedmont has had a long history of
sedimentation, volcanism, terrane accretation and at least three intrusive
episodes. Most of the county is Carolina Terrane; about 15% at the eastern
boundary is Carolina Slate Belt. The western county boundary is very close to
the IP boundary and Cats Square terrane. Phyllite, metasandstones and
metavolcanics are folded into a plunging syncline east of the Gold Hill - Silver
Hill faults.
The oldest and most wide spread rocks in the Charlotte Belt are early
Paleozoic amphibolites and granitic gneiss cut by metagranites and
metadiorites, later gabbros, meta-adamellite, granites (Woodleaf and
porphyritic Churchland and China Grove) and Jurassic diabase dikes and
widespread laumonatization.
The proportion of granite to diorite varies from a few granite dikes
cutting the diorite; in other exposures the granite is so abundant that it
produces a complex of diorite xenoliths. Areas of predominately diorite are
shown separately on the geologic map. The complex is deeply weathered;
exposures of unweathered diorite are found only in streams, unjointed
residual boulders and in deep roadcuts & quarries. The diorites are medium-
grained hypidiomorphic-granular and are composed of approximately 45-60%
subhedral plagioclase (0.3-3.0 mm), 4O-45% hornblende (0.5-2.5 mm) and 3-
15% quartz with accessory biotite (1.0.-2.0 mm), magnetite, pyrite, and
sphene and secondary epidote, calcite and chlorite.
These older metadiorites and metagranites cut by younger post-
metamorphic gabbro stocks probably 400 m.y.o. A large positive gravity
anomaly over the Cleveland gabbro suggests a deep seated intrusion as
interpreted from the gravity map (Mann, 1964).The rocks of the intrusion vary
from olivine gabbro to hornblende gabbro. The rock is dark gray to black and
is fine to medium grained; subophitic to hypidiomorphic granular textures and
are composed of plagloclase (An55 average) (0.4 -5.0 mm), hypersthene (0.5
- .0 mm), augite (1.0 -3.0 mm), hornblende, (up to 6 -7 mm~ mostly 0.2-3.0
mm), olivine (1.0 mm) and accessory biotite (2.0 mm), quartz, apatite,
magnetite and spinel.
The Woodleaf quarry exposes an excellent contact reaction zone
between younger 293-+ 7 m.y.o. unmetamorphosed granite to quartz
monzonite stock and host diorite. The fluid and intrusive nature of the granite
is shown by abundant dikes and sills; diorite xenoliths and roof pendants.
Flow around the larger diorite xenoliths is very common. Granite dikes cut

2. the xenoliths and flow aligned biotite schileren are common. Both the granite
and diorite are cut by late stage vuggy quartz microcline veins containing
abundant euhedral crystal of pyrite, quartz, epidote, chalcopyrite,
molybdenite, calcite and zeolites The Woodleaf granite is medium-grained
(0.5-3.0 mm) hypidiomorphic granular, containing microcline, (1.0-3 mm),
quartz (3 mm) muscovite and plagioclase (1-4 mm), plus accessory biotite
(0.7-1.4 mm), sphene, and secondary epidote (1.5-1.0 mm), chlorite, and
calcite
Two porphyritic alkali granite plutons characterized by large euhedral
microcline phenocrysts are exposed in parts of Iredell, Rowan, Davie and
Cabarrus Counties. The rock is holocrystalline porphyritic containing 10-50
percent euhedral microcline phenocrysts set in a groundmass of 5-20 percent
biotite, 15-30 percent plagioclase, and 20-25 percent quartz. Accessory
minerals include hornblende, magnetite, sphene, ilmenite, zoned zircon and
secondary epidote, leucoxene, and chlorite.
Small metamorphosed ultramafic rocks crop out poorly in the western
part of the county on the Rowan Mills Quadrangle. The rock outcrops appear to
be lenses and are composed of talc, chlorite, and tremolite
The Salisbury shear zone is the name given to a 45 mile long, 2-5 mile
wide zone of nearly striking N20-60 E., vertically dipping (80-85 NW), mylonite
gneiss and ultramylonite schists and unsheared intrusive igneous and large
blocks of-interdispersed metasedimentary relics. The shear zone appears to
be a major internal tectonic feature in the Charlotte Terrane. The
preservation of small unsheared relic blocks of granite and diorite in with
ultramylonite schist, mylonite gneiss, protomylonites, and cataclasites
provides the only evidence for the nature of the original rocks. Sheared rocks
have undergone considerable recrystallization and neomineralization and
fluxion structure. The shear zone is 2-5 miles wide and is 45 miles long
extending from Cabarrus across Rowan and most of Davidson County into
Guilford. Salisbury and Yadkin alkali granite plutons have been emplaced on
the southeast and northwest sides of the shear zone. Smaller lens like bodies
are also present. The Salisbury pluton most common texture is cataclastic.
Full agar, (1971) described the age the pluton to be 410-+10 m.y
Several 1 km. long ridges of quartzite crop out across Rowan County.
These rocks are mostly quartz and muscovite but sometimes contain kyanite
and sillimanite, they have lepidoblastic to porphyroblastic textures; quartz is
broken and recrystallized with sutured contacts. Mica layers delineate chevron
folds.
The Carolina slate belt, is poorly exposed in the southeastern part of the
county as a thick sequence of metamorphosed mafic to intermediate to felsic
volcanic (predominantly calc-alkaline) and volcanoclastic rocks interbedded

3. with locally derived mudstone shales, siltstones, and argillites of late
Precambrian to Cambrian and possibly Ordovician age, metamorphosed to the
lower greenschist facies. They have been folded into a plunging anticline cut
by a shear zone. The Gold-Hill Silver-Hill shear zone is a northeast trending
120 km. long, 3-7 km wide zone of phyllonites and unsheared rocks.