Geometry and Deformation Fabrics in the Central and Southern Appalachian Valley and Ridge and Blue Ridge: Frederick, Maryland to Allatoona Dam, Georgia July 20-27, 1989

113 Pages·2013·6.55 MB·English

by  Nicholas B. Woodward(auth.)

Geometrya nd DeformationF abricsi n
the Centrala nd SouthernA ppalachian
Valley and Ridge and Blue Ridge
Frederick, Maryland to Allatoona Dam, Georgia
July 2o-27, (cid:127)989
Field Trip Guidebook T357
Leader: Nicholas B. Woodward
Associate Leaders:
Steven (cid:127)P'ojtal (cid:127)Zi(cid:127)iam M. Dunne Gautam Mitra
Carol Simpson Mark Evans John Costello
American Geophysical Union, Washington, D.C.
Copyright 1989 American Geophysical Union
2000 Florida Ave., N.W., Washington, D.C. 20009
ISBN' 0-87590-570-6
Printed in the United States of America
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COVER Shear-band cleavage in the Great Smoky Mountains, Tennessee
(King, 1964).
Leader:
Nicholas B. Woodward
1520 Meeting House Road
Knoxville, TN 37931
Associate Leaders-
Steven Wojtal
Oberlin College
Oberlin, OH
William M. Dunne
Department of Geology
University of Tennessee
Knoxville, TN 37996
Mark Evans
University of Pittsburgh
Pittsburgh, PA 15260
Gautam Mitra
University of Rochester
Rochester, NY 14627
Carol Simpson
The Johns Hopkins University
Baltimore, MD 21218
John Costello
Atlanta Testing and Engineering Corp.
Atlanta, GA
IGC FIJW) TRIP 357:
GEOMETRIES AND DEFORMATION FABRICS IN THE CENTRAL AND
SOD'l"'IERN APPAlACHIAN VALLEY AND RIDGE AND BIDE RIDGE
INTRODUCTION of our time in two more localized areas.
Days one through four will be spent in
The Appalachian orogenic belt extends Maryland, eastern West Virginia and northern
over several thousand kilometers (miles) if Virginia, examining structures in the
all its components in the Ouachitas (Texas, Central Appalachians. Days six through
Oklahoma, Missouri), the eastern United eleven will be spent in southwestern
States from Alabama to Maine, and Canada, Virginia, eastern Tennessee and northern
are included. We will only be visiting a Georgia, examining the structures in the
small part of the belt between Washington, Southern Appalachians. Approximately half
D.C. and Atlanta, Georgia (900 kms apart. our time will be spent looking at Valley and
along strike). The goals of the trip are to Ridge structural styles and deformation
introduce the deformation geometries of the fabrics and the other half looking at Blue
different structural provinces on the Ridge structures.
western margin of the Appalachians, and to
examine the typical deformation fabrics that
help us to determine the kinematic evolution OROGENIES
of those geometries. The trip is focused on
the two westernmost geologic provinces of The Appalachians formed during the
the central and southern Appalachians, collapse of the Paleozoic precursor to the
namely the Valley and Ridge Province and the present Atlantic, the Iapetus Ocean (Wilson,
Blue Ridge Province. (Fig. 1) 1966; Hatcher and Odom, 1980). There have
The Appalachian Plateau Province includes been three major peaks of deformation,
predominantly cratonal strata at the western metamorphism and clastic wedge
margin of the Appalachians (the age range at sedimentation, but they vary in occurrence
surface from late Cambrian to early Permian) and intensity in different parts of the
deformed during the late Paleozoic. The mountain chain. They are the Taconic, the
Valley and Ridge Province includes the Acadian and the Alleghany Orogenies
miogeoclinal strata of the North American (Rodgers, 1983). Quite possibly, however,
craton, ranging in age from early Cambrian each of these includes several episodes or
through late Carboniferous, also deformed climaxes of deformation.
primarily in the late Paleozoic. The Blue The Taconic Orogeny is named for the
Ridge Province includes miogeoclinal (?) Taconic Mountains on the New York-New
continental slope/rise sedimentary rocks, England border, and it is most clearly
ranging in age from Late Precambrian through evident in the Northern Appalachians where
early Paleozoic and also the basement rocks deformation, metamorphism and clastic-wedge
on which the slope/rise sedimentary rocks deposition all climaxed in the Middle to
were deposited. The Blue Ridge and the more Late Ordovician. Taconic metamorphism has
eastern tectonic provinces have had a also been identified in the southern Blue
complex polyphase deformation history. Ridge Province in Virginia, Tennessee and
Overall, our entire trip will be spent in North Carolina. Ordovician metamorphic
allochthonous but clearly North American isograds cross-cut at least some of the Blue
derived sedimentary rocks and basement. The Ridge structures in eastern Tennessee,
Central and Southern Appalachians are areas dating them as Taconic. Ordovician
in which much of the development of the synorogenic clastic-wedge sedimentation is
concepts of thin-skinned tectonics occurred also preserved within eastern thrust sheets
(Rodgers, 1949) based, first on field of the southern Valley and Ridge Province
geology, and now aptly confirmed by representing distal debris from the Blue
extensive seismic investigations (Cook, Ridge which was then several hundred
1979). The eastern Blue Ridge Province and kilometers to the east.
the Piedmont Province are all thought to be The Acadian Orogeny is named for the old
accreted terranes, added to North America at French colony of Acadia in eastern Canada on
different times during the evolution of the the Bay of Fundy, and again the deformation
mountain chain (Williams and Hatcher, 1983). and metamorphism related to this event of
Because of the distances within even this Early and Middle Devonian age is best
limited part of the belt we will spend most displayed in the Northern Appalachians. The
T357: 1
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FIGURE 1 W- Washington, D.C., N- Nittany Anticlinorium, C- Cumberland,
MD, Wi · Wills Mountain Anticlinorium, H - Harrisonburg, VA, M · Massa
nutten Synclinorium, S - Shenandoah Synclinorium, R - Roanoke, VA, Wy ·
Wytheville, VA, MC - Mountain City Window, GF - Grandfather Mountain
Window, D · Duffield, VA, CG - Cumberland Gap, TN, K - Knoxville, TN, G ·
Gatlinburg, TN, Du - Ducktown, TN, Ch - Chattanooga, TN, A - Atlanta, GA,
B · Brevard Zone, CO - Coastal Plain. Stipple shows exposures of
crystalline basement rocks. Bold dashed lines show major fold trends of
Central Appalachians. Solid barbed lines show major faults. Dash and dot
line shows field trip route. (after Rodgers, 1970).
largest synorogenic (?) clastic wedge in differing plate margin configurations along
eastern North America, the Catskill delta in strike. Thompson (1982) discussed a very
New York, Pennsylvania and the Virginias, similar deformation style change along
was shed from the Acadian Orogenic belt strike in the Canadian Rockies from the
farther east in New England. There is imbricate thrust structure of the southern
little evidence for extensive Acadian Canadian Rockies to the blind thrust style
deformation outside of the Northern of deformation farther north, which he also
Appalachians, although some radiometric related to stratigraphic variations.
dates in the eastern Piedmont of the The Blue Ridge Province as seen in the
Southern Appalachians are also Middle early parts of the trip is dominated by
Devonian. Precambrian basement rocks with infolded and
The Alleghany Orogeny is named for the infaulted metasedimentary sequences. As
Alleghany Mountain chain in the noted near Harpers Ferry, WV (Day One) and
Pennsylvania-West Virginia segment of the Independence, VA (Day Six), extensional
Appalachians. The deformation and features probably related to initial rifting
metamorphism of this period is roughly of Iapetus are also preserved in the Blue
Carboniferous and Permian in age. Most of Ridge. The Southern Appalachian Blue Ridge
the deformation we will be observing on this in the Great Smoky Mountains, in contrast,
trip is of Alleghanian age. Late Paleozoic locally has at least 8 kms of Precambrian
plutonism is relatively common in the clastic sediment (Ocoee Series) on top of
internal zones of the Southern Appalachians, Precambrian crystalline rocks and little of
and much of the terrane accretion there may the Precambrian crystalline basement is seen
be of that age. The addition of "Avalonian" at the surface. The southwest part of the
terranes in southeastern New England and in Ocoee basin is visited on Day Eleven where
the eastern part of the Southern basement reappears with the metasediments.
Appalachians is also probably Alleghanian. The nature of the boundary between the
In plate-tectonic terms, the Taconic Valley and Ridge and Blue Ridge Provinces
Orogeny is usually associated with the changes dramatically along strike in this
subduction of the northern North American part of the Appalachians. In the Central
continental margin beneath an eastern Appalachians the major fault boundary is the
island-arc terrane. Taconic deformation and Little North Mountain thrust (LNMT), but
metamorphism in the Southern Appalachians that fault occurs in the middle of the
probably had a similar cause although the Valley and Ridge Province juxtaposing the
evidence is scarce. The Acadian Orogeny is western Valley and Ridge and the eastern
usually associated with collision of the arc Valley and Ridge with at least 60 km of
and North America with the European shortening. Strata are relatively
continental mass or a southwestern appendage continuous across the boundary between the
of it, such as Armorica. The Alleghany eastern Valley and Ridge to the Blue Ridge,
Orogeny is the result of the collision of but there are small displacement thrusts in
the southeastern border of North America many places. A major continuous fault
with West Africa. separating the Valley and Ridge and Blue
Ridge appears in Central Virginia and
continues through Tennessee and Georgia
MAJOR CONTRASTS where the major Blue Ridge thrust has at
least 50 km of displacement. As a result we
The Appalachians expose relatively will observe a gradual change in structural
continuous structural belts along a complex style from west to east across the Province
continental margin, and we can observe major boundary in the early part of the trip and a
contrasts between the structures seen at discontinuous change in style later in the
different positions along strike. The trip.
sedimentary section in the Valley and Ridge Although the structural belts appear
Province of the Central Appalachians is continuous along strike, evidence for the
nearly twice as thick as that of the age(s) of deformation is not uniform in
Southern Appalachians and the deformation different areas and it is possible that
style there of surficial folding is in different parts of the "same" structural
marked contrast to deformation farther belts had different peak times of
south. The Southern Appalachian Valley and deformation. Deformation styles and fabrics
Ridge is dominated by surficial thrust also vary along strike. Weak, layer
faults. Willis (1893) suggested that the parallel shortening cleavages are common in
difference was a result of the stratigraphic the Central Appalachians and are rare
packages responding differently during farther south. Penetrative rock fabrics are
deformation. It might also be the result of common in both carbonates and clastics in
T357: 3
the Valley and Ridge of the Central Acknowledgments
Appalachians, although they are only common
in exceptional lithologies in the southern The authors would like to thank the many
Appalachians. colleagues whose contributions, both
Ye hope that the contrasts in structural scientific and editorial, have been called
styles and differences in rock fabrics are upon in our compilation of this trip. Ye
as interesting as the elegant regional would especially like to thank our reviewers
symmetry of the belt as a whole. Dr. John Rodgers and Dr. Richard P.
Nickelsen for their thoughtful and thorough
efforts. Penny Hanshaw of the IGC Committee
and Janet Evans of the AGU provided timely
and essential editorial support for this
project.
DAY ONE - BLUE RIDGE ANTICLINORIUM AND HASSANUTTEN SYNCLINORIUM
IN WESTERN MARYLAND
Steven Yojtal
Oberlin College, Oberline, Ohio
Itinerary: Frederick, MD - Gambrill State Park, MD - Middletown, MD -
Harpers Ferry, YV - Shepardstown YV - Williamsport - MD -
Hancock, MD - Cumberland, MD.
Topographic maps: Baltimore, MD, 1:250,000; Cumberland, MD, 1:250,000.
Geologic maps: Geologic map of Washington County, MD (MD Geol. Survey)
INTRODUCTION unconformably above the basement in the Blue
Ridge anticlinorium (Rodgers, 1972). The
We begin our excursion by exam1n1ng Swift Run Formation, a thin package of
deformed rocks in the Blue Ridge and Valley arkoses, quartzites, slates, and phyllites,
and Ridge Provinces in Maryland (Fig. 1). locally lies on top of the basement in
Ernst Cloos, David Elliott, John Wickham, Maryland (Schwab, 1986). Along strike in
and their students have all participated in Virginia, the equivalent units (Proterozoic
outlining the major geometries of the Z formations, see Day Four) are 3 km thick
structures and their incremental strain (Rodgers, 1972). About 200m (up to 800 m
histories. Individual exposures are along strike to the southwest) of volcanic
visually striking, and their role in the rocks in the Catoctin Formation cover the
regional deformation is well constrained. clastic units; Catoctin feeder dikes cut all
This is, then, an excellent place to examine older units. Metamorphosed to greenschist
Appalachian deformation. grade in the Paleozoic, the Catoctin was
probably once olivine-poor basalts (Reed and
Morgan, 1971) extruded as subaerial (Reed,
REGIONAL STRATIGRAPHIC FRAMnlORK 1955) and subaqueous flows (Lukert and
Mitra, 1986). Catoctin volcanics are about
The oldest rocks in the region are 600 Ma old (Mose and others, 1985), like the
granitoid gneisses and related rocks (1.3 to rift volcanics elsewhere in the belt
1.0 Ga old) exposed in the Blue Ridge and (Williams and Hiscott, 1987).
Piedmont Provinces (Bartholomew, 1984). The Chilhowee Group, which generally
Rocks of similar age and composition crop comprises three formations, lies
out in the Grenville Province of the unconformably on the Catoctin Formation in
Canadian shield (Wynne-Edwards, 1972) and Maryland and Grenville basement elsewhere
form the autochthonous basement beneath the along strike (Fig. 1) (Colton, 1970; Schwab,
Plateau and Valley and Ridge Provinces. 1972, 1986). At most locations, the basal
Late Proterozoic stratified rocks crop out Chilhowee unit is arkosic to quartzitic
T357: 4
the Valley and Ridge of the Central Acknowledgments
Appalachians, although they are only common
in exceptional lithologies in the southern The authors would like to thank the many
Appalachians. colleagues whose contributions, both
Ye hope that the contrasts in structural scientific and editorial, have been called
styles and differences in rock fabrics are upon in our compilation of this trip. Ye
as interesting as the elegant regional would especially like to thank our reviewers
symmetry of the belt as a whole. Dr. John Rodgers and Dr. Richard P.
Nickelsen for their thoughtful and thorough
efforts. Penny Hanshaw of the IGC Committee
and Janet Evans of the AGU provided timely
and essential editorial support for this
project.
DAY ONE - BLUE RIDGE ANTICLINORIUM AND HASSANUTTEN SYNCLINORIUM
IN WESTERN MARYLAND
Steven Yojtal
Oberlin College, Oberline, Ohio
Itinerary: Frederick, MD - Gambrill State Park, MD - Middletown, MD -
Harpers Ferry, YV - Shepardstown YV - Williamsport - MD -
Hancock, MD - Cumberland, MD.
Topographic maps: Baltimore, MD, 1:250,000; Cumberland, MD, 1:250,000.
Geologic maps: Geologic map of Washington County, MD (MD Geol. Survey)
INTRODUCTION unconformably above the basement in the Blue
Ridge anticlinorium (Rodgers, 1972). The
We begin our excursion by exam1n1ng Swift Run Formation, a thin package of
deformed rocks in the Blue Ridge and Valley arkoses, quartzites, slates, and phyllites,
and Ridge Provinces in Maryland (Fig. 1). locally lies on top of the basement in
Ernst Cloos, David Elliott, John Wickham, Maryland (Schwab, 1986). Along strike in
and their students have all participated in Virginia, the equivalent units (Proterozoic
outlining the major geometries of the Z formations, see Day Four) are 3 km thick
structures and their incremental strain (Rodgers, 1972). About 200m (up to 800 m
histories. Individual exposures are along strike to the southwest) of volcanic
visually striking, and their role in the rocks in the Catoctin Formation cover the
regional deformation is well constrained. clastic units; Catoctin feeder dikes cut all
This is, then, an excellent place to examine older units. Metamorphosed to greenschist
Appalachian deformation. grade in the Paleozoic, the Catoctin was
probably once olivine-poor basalts (Reed and
Morgan, 1971) extruded as subaerial (Reed,
REGIONAL STRATIGRAPHIC FRAMnlORK 1955) and subaqueous flows (Lukert and
Mitra, 1986). Catoctin volcanics are about
The oldest rocks in the region are 600 Ma old (Mose and others, 1985), like the
granitoid gneisses and related rocks (1.3 to rift volcanics elsewhere in the belt
1.0 Ga old) exposed in the Blue Ridge and (Williams and Hiscott, 1987).
Piedmont Provinces (Bartholomew, 1984). The Chilhowee Group, which generally
Rocks of similar age and composition crop comprises three formations, lies
out in the Grenville Province of the unconformably on the Catoctin Formation in
Canadian shield (Wynne-Edwards, 1972) and Maryland and Grenville basement elsewhere
form the autochthonous basement beneath the along strike (Fig. 1) (Colton, 1970; Schwab,
Plateau and Valley and Ridge Provinces. 1972, 1986). At most locations, the basal
Late Proterozoic stratified rocks crop out Chilhowee unit is arkosic to quartzitic
T357: 4
'
~,, ___ _
\ ,Del
'---J
Little North Mtn. Th.
43"30'
10km
78"00'
a)
FIGURE la Map showing the general geology of the Blue Ridge Province and a
portion of the Valley and Ridge Province in Maryland, the excursion route
(dashed line), and the locations of stops for Day 1. XX' gives the line
of section for Fig. 2. Barbed solid lines- thrust faults; Thin solid
lines- stratigraphic contacts.
sandstones and conglomerates with Cambrian laterally extensive clastic unit, and 3 to 5
trace and body fossils (Simpson and km of marine carbonate strata. Dolomites,
Sundberg, 1987). In Maryland, up to 60 m of limestones, shales, and local evaporites
phyllites and conglomerates, the Loudoun (Diegel, 1988) in the lower carbonate may
Formation, separate these clastics from the have accumulated in a narrow marine basin
Catoctin (Cloos, 1951). The middle unit is akin to the modern Red Sea (Bond and others,
mainly siltstones, shales, and fine-grained 1984). Detritus in the clastic unit came
sandstone. The upper unit is typically a from the craton to the north and west
clean, quartzitic sandstone with abundant (Colton, 1970). The overlying limestones
Skolithus (Schwab, 1972; Simpson and and dolostones accumulated in peritidal
Sundberg, 1987). Chilhowee detritus, environments on a carbonate bank that
derived from the craton to the west (Brown, stretched from what is now Labrador to what
1970), probably accumulated in coeval is now Alabama and that prograded cyclically
alluvial fan/sand flat (lower unit), mudflat to the southeast (Demicco and Mitchell,
(middle unit), and beach deposits (Fitcher 1982).
and Dieccho, 1986; Simpson and Sundberg, In the Middle Ordovician, Taconic
1987). Thus, Chilhowee strata record a orogenic activity caused the shelf from New
switch from non-marine to marine England to Alabama to subside diachronously
sedimentation during a Cambrian rift-drift below wavebase and receive siliciclastic
transition (Bond and others, 1984; Schwab, detritus from the south and east (Colton,
1986). 1970; Thompson and Sevon, 1982; Shanmugam
The Lower Paleozoic sequence in the and Lash, 1982). Evidence for orogenic
Plateau and Valley and Ridge Provinces is a activity, which included ophiolite
southeast-thickening miogeosynclinal package obduction, is best preserved in the Northern
consisting of a basal carbonate unit, a Appalachians (Rodgers, 1971; Rowley and
T357: 5