gb 1978.book - Carolina Geological Society

David C. Prowell
Figure 2. Contour map on the base of the Tuscaloosa Formation showing the type of crystalline basement at contact localities. Contour
interval: 25 ft. (7.6 m).
Kiokee belt (Crickmay, 1952). The Belair belt is the southernmost
exposed crystalline terrane in eastern Georgia. Prior
to metamorphism, these rocks were tuffs, lapilli tuffs, and
volcaniclastic rocks. Their compositions range from rhyolitic
to andesitic. The oldest phyllites are along the northern
edge of the Belair belt and are characterized by abundant
lapilli tuffs and water-worn rock fragments. Overlying the
lapilli phyllites is a sequence of greenstones containing moderate
to abundant epidote. Above the greenstones is a very
thick accumulation of tuffs and volcaniclastic rocks characterized
by fine-grained textures, graded bedding, and fine
lamination. The rocks of the Belair belt are locally contorted
and have a conspicuous axial plane cleavage that strikes
north-northeast and dips moderately southeast.
The rocks immediately north of the Belair belt are
largely granitoid and amphibolite gneisses, amphibolite, and
intrusive granite of the Kiokee belt. In eastern Georgia, the
typical rock type of the Kiokee belt is a two-feldspar micagneiss.
The most common Kiokee belt rock types in the
vicinity of the Belair fault are hornblende gneiss, biotite
gneiss and schist, and granitoid gneiss. North of Augusta,
amphibolite, mica schist, and intrusive rocks are more common.
Most Kiokee belt gneisses are probably paragneisses,
although some of them could be orthogneisses. The foliation
in the gneisses generally strikes northeast and dips gently to
moderately southeast.
The contact between the Belair belt and the Kiokee belt
is a zone about 0.5 km (0.3 miles) wide that dips moderately
to steeply (45° -75°) southward. Mylonitized, brecciated,
and contorted gneisses and some phyllonites characterize
this contact zone. The contact trends east to east-northeast
across eastern Georgia, terminating at the Belair fault zone
on Fort Gordon Military Reservation (see Fig. 1). The contact
emerges on the east side of the Belair fault zone near
Martinez, Georgia, and trends northeastward into South
Carolina, where it is obscured by overlying Coastal Plain
sediments. Control points on the location of this contact are
shown on Fig. 2. The delineation of the mylonitized Belair-
Kiokee belt contact has been the subject of several geophysical
interpretations (Fig. 3). Daniels, (1974) suggested the
existence of the mylonite zone in western South Carolina on
the basis of steep linear aeromagnetic gradients roughly corresponding
to the phyllite-gneiss contact. Hatcher and others
(1974) further extrapolated the zone on the basis of regional
aeromagnetic data and named it the Augusta fault. The aeromagnetic
map shown in Daniels (1974) suggests that the
Augusta fault bifurcates just northeast of Augusta and that
branches go both north and south of the city. Therefore, it is
unclear which segment west of the bifurcation should be
called the Augusta fault. Hatcher and others (1977) applied
their Augusta fault terminology to the magnetic gradient
south of the city (see Fig. 3). I have chosen to extend the
Augusta fault nomenclature along the magnetic gradient
north of the city of Augusta (see Fig. 1) because the magnetic
gradient coincides with a lithologic contact marked by
mylonitic rocks. This portion of the Augusta fault is critical
to my discussion of lateral displacement along the Belair
fault zone.
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