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GEOLOGIC CONTRASTS ACROSS THE CENTRAL PIEDMONT SUTURE IN NORTH – CENTRAL NORTH CAROLINA
Figure 5. Equal area stereo plots of S H , F H , and H L , L H and S HL in the Hyco Shear zone.
metagranite, biotite gneiss, amphibolite, and metadiorite.
Along much of its northern border, the Cunningham gneiss is
cross-cut by dikes and sills of the Kilgore gneiss. The metamorphism
affecting this unit is difficult to discern due to its
composition, but it appears to be in the amphibolite facies.
The late syn-tectonic suite of NNE-trending granite pegmatites
that intrudes the Country Line gneiss also intrudes the
Cunningham gneiss.
Between Yanceyville and Hyco Lake another granitic
body intrudes into the HSZ. This stock, the Winged granite,
is a coarse grained biotite-muscovite granite which has a
shape resembling a large dextrally deformed winged porphyroclast.
The northern tail of the Winged granite forms a continuous
tabular body which extends for several kilometers.
The age of the Winged granite is uncertain, but the kinematics
inferred from its shape and apparent partitioning of deformation
into an outer highly deformed rim cored by a lesser to
undeformed interior suggests a syntectonic, Alleghanian age,
for this body.
Structure
The HSZ is highly deformed ductile shear zone involving
multiple generations of structures. The most striking feature
of the HSZ units is the gneissic layering which is
overprinted by an ENE to NE striking layer parallel foliation,
S H , that is axial planar to isoclinal folds, F H (Figure 5,
see table 1 for a terminology description). The foliation dips
up to 75° SE near the Carolina zone and decreases to 35° SE
near the Piedmont zone.
Our observations suggest that the F H isoclinal folds may
represent either of the following 1) Carolina zone folds that
have been transposed into concordance with the ENE trending
HSZ and/or 2) folds related to the early development of
the HSZ. Also observed in the HSZ is a second, gently-dipping,
fabric, S HL , which is axial planar to a set of recumbent
tight to isoclinal folds, F HL . S HL has been observed overprinting
the more steeply-dipping S H foliation locally as well
as being overprinted in turn by S H at other locales suggesting
a close temporal relationship between the foliations. A maximum
age constraint for the formation of these fabrics is provided
by the pre- to syn-tectonic ca. 335 Ma Yanceyville
gneiss which is affected by both foliations.
Shear sense indicators are well developed, widely distributed,
and are associated with both S H and S HL . With S H ,
indicators include S-C fabrics, winged porphyroclasts, shear
bands, asymmetric folds and well developed ENE to NE
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