ABSTRACT
Stratigraphy on the eastern flank of the Southern Appalachian Blue
Ridge near the Grandfather Mountain window is arranged in a series
of fault-bounded lithotectonic belts stacked so that the
structural section dips steeply southeast. The Fries block of the
Blue Ridge thrust sheet overlies the Grandfather Mountain window
along the Linville Falls fault. The Laytown belt overlies the
Fries block along the Winding Stairs Mountain fault. The Brevard
zone, bounded at its base by the Ripshin Mountain fault and
bounded at its top by the Yadkin fault, lies on the Laytown belt.
Augen gneiss and granitic gneiss of the Inner Piedmont, here
called Henderson gneiss, sharply abuts the Brevard zone along the
Yadkin fault. It is unlikely that any coherent stratigraphy exists
in the Brevard zone.
All principal foliations in the Grandfather Mountain window, Blue
Ridge thrust sheet, and Brevard zone are the result of the
transposition of an earlier layering or foliation. Brevard zone
mylonites commonly show isoclinally refolded isoclines. The
mylonitic foliation there is the culmination of multiple
deformation. Distinct zones in the Fries block contain a
superimposed cleavage that results in locally transposed,
mylonitic shear zones. These shear zones are sites for retrograde
metamorphism and they are interpreted to be faults, possibly
splays off a thrust that may emerge as the Linville Falls fault.
Lineations were produced as a result of transposition. The
principal lineation in the Grandfather Mountain window is older
than the principal lineation in the Blue Ridge and the Brevard
zone. Interpretations of shear sense in the Brevard zone based on
orientations or reorientations of the lineations are not
appropriate.
Shear across low angle oblique crenulation cleavage is
consistently dextral in the Brevard zone. The cleavage event is
interpreted to have occurred in the latter stages of late
Paleozoic ductile deformation and retrograde metamorphism in the
Brevard zone. The cleavage geometry suggests dextral strike-slip
motion on the Brevard zone.
Theoretical models for irrotational structures in two-dimensional
plane strain demonstrate that: (1) lines of material particles
lying in an oblique irrotational orientation make an angle, a,
with the shear zone boundaries whose vertex indicates the shear
sense for the simple shear component and (2) the oblique
irrotational direction could experience a component of simple
shear equal in sign to that of the shear zone.
Bobyarchick, A.B., 1983. Structure of the Brevard Zone and Blue
Ridge near Lenoir, North Carolina, with observations on oblique
crenulation cleavage and a preliminary theory for irrotational
structures in shear zones. Unpublished PhD dissertation,
State University of New York at Albany. 306pp., +x; 5 folded
plates (maps)
University at Albany Science Library call number: SCIENCE
MIC Film QE 40 Z899 1983 B63
Copies of this PhD dissertation can be ordered
from Proquest UMI
Front matter (title,
table of contents, abstract, acknowledgements) - 0.4MB pdf
file
Photo pages in dissertation
(greyscale
photos with captions): - 21.2MB pdf file
Plate 1a (Fig 2-1A) - Geologic
map of the Buffalo Creek area (North Carolina) 7.4MB
pdf file
(uncoloured geologic map;
scale 1:24,000)
Plate 1b (Fig 2-1B) - Explanation
of Geologic map - Map units - Buffalo Creek area (North
Carolina) 0.7MB pdf file
Plate 1c (Fig 2-1C) - Explanation
of Geologic map - Structure - Buffalo Creek area (North
Carolina) 1.3MB pdf file
Plate 1d (Fig 2-1D) - Geologic
cross section - Buffalo Creek area (North Carolina) scale
1:24,000 0.4MB pdf file
Plate 1e (Fig 3-12) - Contoured
stereoprojections of foliations - Buffalo Creek area (North
Carolina) 0.7MB pdf file
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