The Christiansburg map area consists of about 19 square miles in Montgomery County, Virginia, and is underlain by sedimentary rocks ranging in age from Middle Cambrian to Middle Ordovician. Post-Ordovician strata have been eliminated by thrusting and erosion. From south to north the rocks belong to five fault blocks: the Max Meadows, Pulaski, Saltville, Salem, and Catawba blocks. The Max Meadows block contains only the Middle Cambrian Rome Formation, the oldest rocks exposed within the area. The parautochthonous Saltville block includes rocks from Upper Cambrian to Middle Ordovician in age, which are exposed in windows of the Pulaski fault block. The Pulaski block contains highly fractured and brecciated Cambrian carbonates. The Salem block contains rocks ranging in age from Middle Cambrian to Lower Ordovician. The Salem fault terminates west of Christiansburg, Virginia. Rocks of the Catawba block range from Middle Cambrian to Mississippian in age, but only the section up to the Middle Ordovician is exposed in the map area. The windows through the Pulaski thrust sheet expose the large Christiansburg anticlinorium of the Saltville fault block. The size of each window is proportional to the size of the anticlinal fold developed on the crestal portion of the anticlinorium. The faulting may have occurred shortly after deposition of the Mississippian strata exposed in the Price Mountain window north of the area. The apparent parallelism of the thrust sheets and the overridden strata indicates that much of the present structural relief was formed after emplacement of the thrust sheets. / Master of Science

The Saltville thrust sheet in the southwest Virginia portion of the Appalachian foreland fold and thrust belt generally has very little penetrative deformation. At the southern termination of Walker Mountain however, a continuous 10-15 km zone along strike is highly strained and polydeformed. In this area a NW-trending mesoscopic solution cleavage and associated buckle folds are obliquely superimposed on the regional northeast structural trend. Values of penetrative strain, determined from syntectonic fibrous mineral growths in pressure fringes, vary along strike and vertically within the thrust sheet and indicate up to 50% shortening approximately orthogonal to cleavage. Fibers are virtually straight and undeformed reflecting a nearly coaxial strain history associated with cross-structural evolution. The cross-structures deform the Saltville sheet as well as the leading edge of the Pulaski sheet and were not rotated into their present orientation, but were initiated and evolved oblique to the northwest direction of tectonic transport. Cross-structural development is best explained by the oblique propagation of a portion of the frontal-tip of the evolving Saltivlle thrust in response to varying degrees of detachment. The variable ease with which the decollement was able to migrate through the rocks created zones of differential movement in the overlying sheet and the generation of locally high strains in the tip region. Spatial variation in strain and in the orientation of structural elements may be used to delineate zones of differential thrust movement. / M.S. / Bibliography: leaves 57-65.

Folding prior to thrust-sheet emplacement is proposed to explain presence of overturned synclines in the footwalls of many thrust-faults in the Appalachian foreland fold- and thrust-belt of southwest Virginia. Investigation of relations in the footwalls of the Saltville and St. Clair thrust-sheets near the Southern-Central Appalachian juncture indicates presence of at least two distinct types of footwall structures: 1)isolated forelimbs of thrust-truncated asymmetric ramp-generated anticlines, and 2)areally extensive overturned subthrust synclines. Mesoscopic fabric data and strain states indicate rotation of bedding by folding prior to thrust-sheet emplacement rather than drag folding during thrusting. Low angles between bedding and cleavage planes and low strain values on the back limbs of folds at thrust terminations (Sinking Creek anticline) and in hangingwall strata seems to indicate folding was largely accomplished by flexural flow in units of relatively low mechanical strength. / M.S.

M.S.

Bouguer gravity anomalies at 1870 locations on the central Piedmont of Virginia from 37° 37' N to 37° 52' N and 77° 44' W to 78° 23' W display patterns of variation produced by upper crustal density contrasts and thickening of the crust in a WNW direction. No other deep sources are evident. Upper crustal density contrasts are associated with rock units known from geologic mapping. ‘The subsurface distribution of these rock units interpreted from seismic reflection data was confirmed by measured variations in gravity. A two-dimensional model analysis indicates the following average in situ density values for the principal formations: Arvonia Formation-2.77 gm/cc, Columbia Granitoid-2.75 gm/cc (tonalite) and 2.73 gm/cc (pegmatite), Chopawamsic Volcanics- 2.77 gm/cc (felsic units), and 2.79 gm/cc (mafic units}, Catoctin/ Lynchburg-2.815 gm/cc, Maidens Gneiss-2.775 gm/cc, Grenville Basement- 2.71 gm/cc. Gravity and seismic data are consistent with the existence of a major thrust fault at depths between 9 km and 16 km that separates Grenville Basement rocks from younger Catoctin/Lynchburg rocks. The slight eastward dip of this thrust fault beneath the western part of the area increases significantly east of 78° 05' W. Gravity anomalies suggest the existence of several mafic inclusions within the Columbia Granitoid that were not identified by geologic mapping. / Master of Science

Broken-formations (Hsu, 1974; Harris and Milici, 1977) occur in the lower part of the Pulaski thrust sheet and contain some of the most strongly deformed sedimentary rocks in the Valley and Ridge province of the southern Appalachians. Deformation in this zone ranges from grain-scale cataclasis to regional-scale faulting. The broken-formations are distinguished from rocks structurally higher on the sheet and from rocks of the underlying Saltville sheet by (1) a sharp increase in the variability of fold and fault styles, (2) greater ranges in fold plunges and dips of axial surfaces, (3) a low degree of preferred orientation of folds and faults, (4) an increase in the frequency of mesoscopic structures, and (5) the presence of Max Meadows tectonic breccia. Structural analyses indicate that deformation in the broken-formations is Alleghanian in age and that the deformed zone formed under elastico-frictional conditions, possibly under elevated fluid pressures with temporally variant stresses and that lithology may have played an important role in localizing the broken-formations along the base of the Pulaski sheet. / Ph. D.

The Fries Fault, a 1.2-2.3 km wide zone near Riner, is a major tectonic discontinuity in the Blue Ridge geologic province, characterized by progressive stages of continuous ductile deformation. Trending northeast with a shallow to moderate southeast dip, this fault juxtaposes Little River Gneiss on the southeast against Pilot Gneiss and the Chilhowee Formation to the northwest. A 0.8-1.2 km wide subzone of protomylonite within the Little River Gneiss grades into a 0.5-1.0 km wide mylonite subzone, the latter containing narrow bands of phyllotactic ultramylonite ranging in width from centimeters to tens of meters. Mylonitization is reflected by a marked reduction in grain size, elongation of quartz and fracturing of feldspar, all concomitant with the development of a mylonitic foliation (S_m). Ductile deformation processes involving grain elongation, recovery and recrystallization, combined with chemical processes (primarily pressure solution), are the dominant strain-accommodation mechanisms in the formation of S_m. Rocks within the fault zone have undergone four phases of Paleozoic deformation. An early S₁ foliation has been nearly completely transposed by S_m(S₂), which dominates across most of the area. The development of S_m was accompanied by a retrogressive metamorphism that altered basement rocks from lower amphibolite to greenschist facies. Chilhowee Group rocks remained at lower greenschist facies. Post-faulting deformation produced an S₃ crenulation cleavage associated with northeast trending, overturned F₃ folds. Subsequent refolding produced open, northwest trending F₄ folds. Although the bulk deformation is progressive simple shear, flattening is increasingly dominant during the later stages of deformation. / Master of Science

This kyanite quartzite deposits at Leigh, Baker and Willis Mountains located in the south central Virginia Piedmont were investigated to determine their genesis, extent, and geologic and petrographic character. Kyanite quartzite in Virginia typically contains 20-40 per cent kyanite, 0-5 per cent pyrite, 0.5-1.5 per cent rutile, a per cent or so of mica or clay with the balance quartz. They occur as single beds within metamorphic rocks ranging from slates and phyllites of the greenschist facies south of Leigh Mountain, to schists and gneisses of the amphibolite facies at Baker and Willis Mountains. Post-kyanite hydrothermal alteration along fractures has altered large segments of the Baker Mountain deposit to clay and topaz. The protolith of kyanite quartzite is believed to have been extraordinarily pure mixture of quartz and kaolinite which was produced by either Iateritic weathering or by circulating meteoric waters. Isochemical regional metamorphism is believed to have occurred in a high pressure, moderate temperature environment in which water was either deficient or able to escape. Fluorine may have had a catalytic effect in promoting kyanite crystallization. No evidence was found of hydrothermal introduction of alumina, or localization of kyanite as a result of differential stress. The rocks enclosing kyanite quartzite in the Leigh Mountain area are believed to be basal members of the lower Paleozoic (?) Volcanic-Slate series. The gneisses surrounding Willis and Baker Mountains may be more highly metamorphosed, infolded remnants of the same series. The kyanite deposits of Virginia are extensive and well situated for mining. Possible reserves of kyanite quartzite containing over 25 per cent kyanite available for open pit mining are measured in tens of millions of tons.

This study was undertaken in order to learn the relationships between clay minerals of stream sediments and the clay mineralogy of corresponding source materials. The York River tributary system was selected to conduct such a study because of its moderate size and its geographical and geological setting. The tributary basin spans the entire Piedmont and most of the Coastal Plain before reaching West Point, Virginia, and it covers 2242 square miles. River sediments and weathering products (source materials) of the basin were sampled in such a way that both were faithfully represented. Stream sediment samples were taken at closely spaced sites as cores, grab samples, and scoop samples from the channel bed. Source material samples were taken after reconnaissance of the area from road outs, cultivated fields and forests. Surface and subsurface source samples were collected. Five small tributaries of the system were similarly sampled in greater detail. X-ray analyses of more than 700 samples were made using powder diffraction techniques and a General Electric recording diffractometer. Filtered Cu-K radiation was used. Each sample was analyzed untreated as an oriented aggregate. Further X-ray analyses where necessary included glycolated and heat treated samples. Clay minerals of source materials and stream sediments of the York River tributary basin are naturally grouped into five categories on the basis of first-order basal spacings. Minerals identified are kaolinite, illite, expandable illite. typical vermiculite atypical vermiculite, montmorillonite and mixed-layer clay minerals involving 10 A and 14 A layers. Kaolinite is present in all source area samples Vermiculite is the next most frequent source mineral followed by illite. Montmorillonite is highly sporadic in occurrence and is a minor constituent in the source area. The stream sediments contain al1 the minerals found in the source area. No new minerals were observed in the stream environment. The frequency distribution of most minerals is different in sediments. Kaolinite and vermiculite occur in all stream sediments. Illite occurs in all sediment samples of the Mattaponi and Pamunkey tributaries and its reflections become more intense in the lower part of the system. Montmorillonite occurs in more than 86 per cent of the sediments of the Coastal Plain portion of the system. Mixed-layer clay minerals become less frequent in the streams of the basin in contrast to their frequency in the source materials and become more pronounced downstream. The intensity of X-ray reflections for source material clay minerals is typically 2-3 times as intense as those of stream sediments. Physical mechanisms are postulated to explain the decrease in mixed-layer structures, the increase in illite intensity downstream and the increase in the frequency of occurrence of montmorillonite in the sediments of the lower parts of the stream systems. Mixed-layer minerals become unmixed through a highly selective erosion and transportation process which results in removal of the clay in units of structure. This physical unmixing provides an explanation of the increase in illite reflections in sediments in the lower part of the stream. Montmorillonite is more frequent in the lower part of the stream because of its greater mobility than the other minerals. Results of this study may require that previous studies of modern sediments be re-evaluated in recognition of the appearance of atypical vermiculite in the source area and the process of unmixing of mixed-layer clay minerals. / Ph. D.

The Goose Creek area in parts of Roanoke, Botetourt, and Bedford counties, Virginia, comprises about 170 square miles of complexly folded and faulted Precambrian and Paleozoic rocks of the Blue Ridge and Great Valley physiographic provinces. The Precambrian rocks are divided into three different types of gneisses on the basis of their textures. These are unconformably overlain by Cambrian rocks of the Unicoi formation, Hampton shale, Erwin quartzite, Rome formation, Bilbrook dolomite, and Conococheague formation. The total thickness of the Precambrian gneisses is about 7,500 feet and that of Cambrian formation is 10,000 feet. The Ordovician Bffna and Fetzer limestones are about 30 feet thick and the Liberty Hall and Martinaburg shales are about 800 feet thick. Silurian-Lower Devonian rocks represented by the Clinch, Clinton, and Helderberg formations are 15 (?) to 300 feet thick. Additional unclassified shales are of Devonian age. Locally Quaternary deposits of colluvium, older terrace gravels, and alluvium cover all of the above. One of the major structural features of the area is the nearly flat Blue Ridge thrust which extends across most of the area. The Blue Ridge thrust plate is breached by Goose Creek in the southeast -part of the area. The displacement of the thrust is at least six miles. The Precambrian rocks of the Blue Ridge fault block are believed to be the core of a large overturned northeasterly-trending anticlinorium. Many similar northeasterly-trending folds, which are mostly open or only slightly overturned to the northwest, are found in the frontal part of the Blue Ridge thrust plate and in the underlying rocks. A few northwesterly-trending cross folds were developed in rocks both above and below the thrust and were formed contemporaneously or slightly later than the faulting. Another major structure, probably the Pulaski thrust fault, is shown in a window cut by the Salem (?) fault at Coyner Mountain. If the correlation of the Pulaski fault is correct then the minimum displacement must bell miles. Many smaller faults and folds also indicate strong compressive forces in a northwest-southeast direction. The cross folds are believed to have been developed by differential northwesterly movement of the fault blocks. The differential movements are believed to have resulted from deflection around buttresses in the Appalachian Valley, although there is a possibility that the deforming force shifted to a more westerly direction. The Blue Ridge province is represented by resistant parts of the uneroded Blue Ridge thrust block. The Great Valley province in the northwest part of the area is underlain by soft shales and carbonate rocks and has encroached on the edge of the Blue Ridge thrust plate. Southwestward-flowing Glade Creek and its main drainage area is similar to the Great Valley in physiography and type of bedrock. It extends northeast into a breached area of the Blue Ridge thrust where its headwaters are captured by southeast-flowing Goose Creek. The geologic history of the Goose Creek area can be summarized as follows: (1) deposition of Late(?) Precambrian sediments; (2) folding and faulting of the Precambrian rocks accompanied by metamorphism, granitization, and intrusion that probably occurred during or prior to a sub-Cambrian orogeny which may have produced the configuration of the Appalachian geosyncline; (3) cannibalism during earliest Cambrian time, supplying the lowest Cambrian elastic sediments; (4) deepening of the Appalachian geosyncline to receive the thick carbonate sediment from Lower Cambrian to Middle Ordovician; (5) resumption of cannibalism on the elevated lands to the southeast from Middle Ordovician to Lower Mississippian time, supplying younger clastic sediments; (6) folding and faulting of the Precambrian and Paleozoic rocks during the Appalachian orogeny; (7) peneplanation of the newborn Appalachian at the summit level of the Blue Ridge mountains in Tertiary(?) time; and (8) intermittent uplifting, trenching,and tilting of the peneplain and other ero~ion surfaces from Tertiary(?) to the present. The mineral resources include limestone, dolomite, iron and shale. Once productive low-grade iron deposits are now no longer profitable. The ground water supply is plentiful and a potential asset for industry. The beat aquifers are the unconsolidated deposits and some of the carbonate rocks of the Elbrook and Rome formations. / Ph. D.