Virginia Piedmont

VIRGINIA DIVISION OF MINERAL RESOURCES PUBLICATION 59

GEOLOGY OF THE SOUTHWESTERN VIRGINIA PIEDMONT

James F. Conley

COMMONWEALTH OF VIRGINIA

DEPARTMENT OF MINES, MINERALS AND ENERGY DIVISION OF MINERAL RESOURCES Robert c. Milici, commissioner of Mineral Resources and state Geologist

CHARLOTTESVILLE. VIRGINIA 1 985 VIRGINIA DIVISION OF MINERAL RESOURCES PUBLICATION 59

GEOLOGY OF THE SOUTHWESTERN VIRGINIA PIEDMONT

James F. Conley

COMMONWEALTH OF VIRGINIA

DEPARTMENT OF MINES, MINERALS AND ENERGY DIVISION OF MINERAL RESOURCES Robert C. Milici, Commissioner of Mineral Resources and State Geologist

CHARLOTTESVI LLE. VIRGI NIA 1 985 FRONT COVER: Polydeformed gneiss from the Fork Mountain Formation near Fieldale, Henry County. VIRGINIA DIVISION OF MINERAL RESOURCES PUBLICATION 59

GEOLOGY OF THE SOUTHWESTERN VIRGINIA PIEDMONT

James F. Conley

COMMONWEALTH OF VIRGINIA

DEPARTMENT OF MINES, MINERALS AND ENERGY DIVISION OF MlNERAL RESOURCES Robert C. Milici, Comrnissioner of Mineral Resources and State Geologist

CHARLOTTESVI LLE. VIRGINIA 1985 DEPARTMENT OF MINES, MINERALS AND ENERGY

Richmond, Virginia

O. GENE DISHNER, Director

COMMONWEALTH OF VIRGINIA DEPARTMENT OF PURCHASE AND SUPPLY RICHMOND

1985

Portions of this publieation may be quoted if credit is given to the Virginia Division of Mineral Resources. It is recommended that reference to this report be made in the following form: Conley, J. F., 1985 Geolog:y of the southwestern Virginia Piedmont Virginia Division of Mineral Resourees Publieation 59,33p. CONTENTS

Page

The Lynchburg Group, a repetitive sequenee of ophiolites and their cover rocks? ...... 7

Metamorphic age dates from rocks of the Lynchburg Group ...... 8

Area III. Sauratown Mountains anticlinorium ...... 15

Area V: Central Virginia volcanic-plutonic belt ...... '..... 18 Metavolcanic and metasedimentary rocks ...... 18

Sauratown Mountains anticlinorium ...... 2I Central Virginia metavolcanic-plutonic belt ...... 21 Unnamed faults and shear 2ones...... 29

Termination of the Smith River allochthon to the southwest ...... 24 Probable thrust faults at the base of the ophiolites? in the Lynchburg Group ...... 25 Thrust faults bounding the Candler Formation ...... 25

Significance of ophiolites? in the Lynchburg Group ...... 2G A reinterpretation of the James River synclinorium ...... 2G

ILLUSTRATIONS

Plate Page Geologic map of southwestern Virginia Piedmont ... In Pocket Figure COVER: Polydeformed gneiss from the Fork Mountain Formation

3. Geologie map showing metamorphic grade ...... b

5. Discrimination diagram for Ti, Zr, and Y ...... 8 6. Stratigraphic relationships of rocks in the Smith River allochthon ...... g 7. Photomicrograph of mica schist member of the Fork Mountain Formation ...... 12 8. Biotite gneiss member of the Fork Mountain Formation ...... 18 9. Biotite gneiss member of the Fork Mountain Formation ...... lg 10. Stratigraphic relationships of rocks in the Sauratown Mountains anticlinorium ...... l5 11. Stratigraphic relationships of rocks in the Danville basin ...... 18 12. Block diagrams showing original interpretation and reinterpretation of the "James River

TABLE

Chart of stratigraphic units used by various authors ...... 27 GEOLOGY OF THE SOUTHWESTERN VIRGINIA PIEDMONT

James F. Conley

ABSTRACT attempt to unify the geologic mapping of various people who have worked on this project and to The area discussed in this report has a somewhat update the interpretations of the geology and show rectangular shape and is located in the southwest- the importance in these interpretations to the re- ern Virginia Piedmont. It comprises 31 7.5-minute gional geologT of the Piedmont and Blue Ridge quadrangles and is the largest area in the Piedmont provinces in southeastern U.S. The compiled map of Virginia geologieally mapped at 1:24,000 seale. includes locations of mines and mineral deposits The geology of this region is naturally subdivided (Plate). into five distinct areas that are generally separated The area is wholly contained within the Inner from each other by either normal or thrust faults. Piedmont physiographic province (Fenneman, These areas are: the Blue Ridge anticlinorium, the 1938) and is situated about 10 miles southeast of Smith River allochthon. the Sauratown Mountains the Blue Ridge escarpment. The land surface is anticlinorium, the Danville Triassic basin, and the a well dissected rolling terrain. The northwestern central Virginia voleanic-plutonic belt. Individual half of the area is more rugged than other parts units that underlie each of these areas are described of the area and contains monadnocks typical of the and stratigraphie relationships are discussed. Nor- Inner Piedmont. mal and thrust faults which bound the five areas, The area is contained within parts of Patriek, and folding which has occurred within each area Henry, Franklin, and Pittsylvania counties. The are deseribed. The stratigraphy and strueture of south-central and western parts of the area are the southwestern Piedmont are reinterpreted be- drained by the Smith River and its tributaries; the cause it was found that rocks previously thought southeastern part of the area is drained by the Dan to be part of the Evington Group on the southeast River and its tributaries, and the north-central and limb of the "James River synclinorium" are actually northwestern parts of the area are drained by the part of the Smith River allochthon. In addition, Pigg River and its tributaries. The largest cities new stratigraphic relationships are reported for the in the area are Bassett, Danville, Martinsville, and southwestern part of the "James River synclino- Rocky Mount. The area is served by U. S. highways rium.t' 29,58,220,and 360; by State highways 40, 41,57, and 87 and by a network of State roads. The area is served by three lines of the Norfolk and Southern INTRODUCTION Railway System. One of these lines eonnects Roa- noke with Martinsville and other points to the south; The area discussed in this report is in the south- the seeond connects Lynchburg and with Danville western Virginia Piedmont and covers a somewhat and points southward, and the third line connects rectangular area about 48 miles in an east-west Martinsville with Danville and points eastward. direction by approximately 32 miles in a north- Red and yellow podzolic soils (Hunt, 1972) are south direction and comprises 31 7.5-minute quad- developed on the rocks of the region. A charaeter- rangles (Figure 1). This group of quadrangles istic of these soils is the development of a deep forms the largest geologically mapped area at a saprolite forming the C soil-horizon. In areas un- scale of 1:24,000 in the Virginia Piedmont, and it derlain by rocks that are susceptible to chem- is one of the largest areas, if not the largest area, ieal weathering (especially quartzo-feldspathic mapped in this detail in the Piedmont of the gneisses of this region), the saprolite is as much southeastern U.S. as 150 feet (45 m) thiek. Mica schists, which are Field mapping of individual 7.5-minute quadran- extremely resistant to chemical weathering, de- gles was begun in 1966 and was continued to 1979. velop very shallow soils and subsoils. They underlie During this time many ideas both about the re- upland and mountainous temains. Gneisses and gional geology and about the interpretation of the gabbroic rocks decompose readily under ehemical local geology have changed, and many previous weathering. They produee deep saprolites and un- concepts have been slightly to drastically modified derlie relatively flat-bottomed basins and lowlands. as neril/ data beeame available. This report is an In contrast metabasalts, amphibolites, diabase, and VIRGINIA DIVISION OF MINERAL RESOURCES

\ aeorono ROANOKE 1\/ FRANKLIN '-i.

,? PITTSYLVANIA .J.:-J l\. HENRY .r X.i') Y- /.17 \- PATR I CK n-t' l-:l'---r\,, '{'.. ,1 -lyn, t'^* j

{' '\-- l- r4---( ,--\t :--t' -- Y--': -\

Figure 1. Iocation map showing quadrangles mapped atl:24,000 scale. 1. Boones Mill quadrangle (McCollum, unpublished reconnaissance map). 2. Redwood quadrangle (McCollum, unpublished reconnaissance map). 3. Moneta SW quadrangle (McCollum, unpublished reconnaissance map). 4. Smith Mountain Dam quadrangle (Conley, Berquist and Marr, unpublished reconnaissance map). 5. Leesville quadrangle (Conley, Berquist and Marr, unpublished reconnaissance map). 6. Ferrum quadrangle (McCollum, Conley and Henika, unpublished reconnaissanee map). 7. Rocky Mount quadrangle (MeCollum, Open File Report, Virginia Division of Mineral Resources). 8. Gladehill quadrangle (McCollum, Open File Report, Virginia Division of Mineral Resources). 9. Penhook quadrangle (Conley, Piepul, Robinson and Lemon, unpublished manuseript map). 10. Sandy Level quadrangle (Berquist, unpublished manuseript map). 11. Pittsville quadrangle (Marr, 1984). 12. Gretna quadrangle (Thayer, unpublished manuscript map). 13. Philpott Reservoir quadrangle (Conley and Henika, 1970). 14. Bassett quadrangle (Henika, 1971). 15. Snow Creek quadrangle (Conley and Henika, 19?3). 16. Mountain Valley quadrangle (Conley, Piepul and Lemon, unpublished manuscript map). 17. Callands quadrangle (Berquist unpublished manuscript map). 18. Chatham quadrangle (Marr, 1984). 19. Spring Garden quadrangle (Henika and Thayer, 1980). 20. Martinsville West quadrangle (Conley and Toewe, 1968). 21. Martinsville East quadrangle (Conley and Henika, 1973). 22. Axton quadrangle (Price and others, 19808). 23. Whitmell quadrangle (Priee and others, 1980A). 24. Mount Hermon quadrangle (Henika, 1977). 25. Blairs quadrangle (Henika, L977). 26. Priee quadrangle (Conley and Henika, 19?3). 27. Spray quadrangle (Conley and Henika, 1973). 28. Northeast Eden quadrangle (Price and others 19808). 29. Brosville quadrangle (Price and others, 19804'). 30. Danville quadrangle (Henika, 1977). 31. Ringgold quadrangle (Henika, L977). PUBLICATION 59

-naa{-lia'#ar-^;

Figure 2. Regional geologic map showing locations of five areas that are underlain by a distinctive sequence of rocks. Each area is noted by Roman numerals. ultramafic rocks, which are unstable under chem- sequence of rocks. These areas are generally sep- ical weathering form thin, clay-rich soils which arated from each other either by a thrust or by protect the chemically unstable rocks from further a normal fault (Figure 2). These areas are from weathering. Thus these rocks generally underlie southeast to northwest: I. The Blue Ridge anti- hills or mountainous terrain. The Triassic sedimen- clinorium, II. The Smith River allochthon, III. The tary rocks of the Danville basin develop soils of Sauratown Mountains anticlinorium, IV. The Dan- shallow to intermediate depth and the basin at ville basin, and V. The central Virginia metavol- present is a topographic depression. Along the canic belt. western edge of the basin, tightly cemented Triassic sandstone produces a pronounced escarpment, Anne I: Blup RtncP ANtrcr,tNontuu which contrasts with the low rolling topography of the basin interior. The term Blue Ridge anticlinorium is, in part, a misnomer beeause in Virginia, rocks of the Blue STRATIGRAPHY Ridge anticlinorium are not eonfined to the Blue Ridge physiographic province. In fact, the major The region of this report is naturally divided into part of the area underlain by these rocks is located five smaller areas, each underlain by a distinctive in the northwestern part of the Piedmont province. VIRGINIA DIVISION OF MINERAL RESOURCES

Rocks contained within the Blue Ridge anticli- dates (Mose and Conley, 1983) indicate that the norium crop out in the northwestern part of the rocks in the axial zone of the Otter Creek and study area (Plate and Figure 2); they are bounded Cooper Creek anticlines are the same age as the on the southeast by the Smith River allochthon. Lynchburg proper. Recent geologic mapping by the In the area of study, two major stratigraphic units, writer in the Lynchburg area and reexamination the Lynchburg Group and the Candler Formation, of the Moneta-Bells area now leads him to the are recognized in the anticlinorium. These two conclusion that all rocks previously called Moneta units are considered to be of iate Precambrian age. Gneiss are part of the Lynchburg Group. Therefore They are located on the southeastern limb of the the name Moneta Gneiss is not recognized as a anticlinorium and overlie Grenville basement rocks formational name in this report. that core the structure. The name Alligator Back Formation is applied to the interlayered schist-gneiss sequence contain- Lynchburg Group ing mafic and ultramafic rocks, graphite schists, and marble that forms the top of the Lynchburg The Lynchburg Group, named the Lynehburg Group. Rankin, Espenshade, and Shaw (1973) corre- Formation by Jonas (1927) for the City of Lynch- lated the Alligator Back with the so-called Eving- burg, Virginia, is exposed across the northwestern ton Group, which supposedly overlies the Lynch- part of the area of this report. Furcron (1969) raised burg. Data presented later in this paper shows that the status of the Lynchburg from that of a formation much of the Evington Group is actually the upper to that of a group and named the lower massive part of the Lynchburg Group. gneisses of the Lynchburg the Bunker Hill For- mation and the upper gneiss, schist, and marble Ashe Formation sequence the Fauquier Formation. Rocks on strike with the Lynchburg to the south in North Carolina The Ashe Formation is a two-mica plagioclase were named the Ashe Formation by Rankin (1g20); gneiss in which biotite is the predominant mica. later Rankin, Espenshade, and Shaw (1gZB) sub- The gneiss generally contains 30 to 45 percent divided the Ashe into two formations. They retained qluarlz,35 to 40 percent plagioclase and up to 20 the name Ashe Formation for the lower clastic percent biotite. Oligoclase is the common feldspar sequence and named a sequence of gneisses, met- in the Ashe Formation and microcline has been apelites, amphibolites, and marbles that makes up identified in only two samples. Muscovite is not the upper part of the unit, the Alligator Back present in all samples but, in a few thin sections, Formation. These two formations have been makes up as much as 15 percent of the rock. Other mapped by Espenshade and others (lg7b) in the minerals are allanite with overgrowths of clinozoi- Philpott Reservoir quadrangle and along the west- site, sphene, apatite, and opaque minerals. The rock ern boundary of the Rocky Mount quadrangle is uniform in composition except for gneissic band- within Area I of this report. In this report the ing produced by oriented micas. The top of the Ashe Lynchburg Group consists ofthe typical Lynchburg is placed at its contact with a sequence of ultramafic as seen at Lynchburg, and the Ashe and Alligator rocks, metagabbros, and metabasalts belonging to Back formations are here described. It also includes the Alligator Back Formation which structurally the Moneta Gneiss as described next, and parts of overlies the formation. The Ashe Formation in the the Evington Group as described later. Cooper Creek anticline contains very little amphib- In this report (following the usage of Furcron, olite, metagabbro, and ultramafic rock. A large 1969), the Lynchburg is raised in rank from for- body of ultramafic, metagabbroic and metabasaltic mation to group. The Ashe Formation is used to rocks that underlies Brier Mountain and trends designate the massive plagioclase gneiss atthe base across the central portion of the Cooper Creek of the Lynchburg Group in the core of the Cooper anticline might be part of the Alligator Back Creek anticline. Amphibolite grade gneisses form sequence that has been folded into the Ashe. Graph- the core of the Cooper Creek and Otter Creek ite, which is ubiquitous in other metasedimentary anticlines. The higher rank rocks in the cores of parts of the Lynchburg, is absent from the Ashe these structures were correlated (Conley and Hen- in the Cooper Creek anticline. ika 1970), with the Moneta Gneiss named by Pegau The Ashe Formation in the Cooper Creek anti- (1932). Rankin, Espenshade, and Shaw (1gZB) con- cline is at higher metamorphic grade than the rest sidered the Moneta, the Ashe, and the Lynchburg of the Lynchburg in the area and contains peg- formations to be correlatives. Recent mapping and matites and small granitoid bodies not present in petrologic studies by the writer and Sr/Rb age the overlying units of the group. This would suggest PUBLICATION 59

EXPLANATION UNMETAMORPHOSED SEDIMENTARY CONTACT LINES ffi ROCKS FAULT- U , UPTHROWN u uNDIFFERENTIaTED tGNEous SIDE; D, DOWNTHROWN SIDE; T, UPPER SHEET; W AND METArcNEous RocKS --T

GREENSCHIST FACIES ROCKS HACHURE TOWARD m <<- ISOGRAD- HIGHER GRADE ,,...f , F---- AMPHIBOLITE FACIES ROCKS RELICT ISOGRAD BETWEEN n.!/ ^) '4'Jf1 STAUROLITE AND SILLIMANITE;./ /' HACHURE TOWARD HIGHER i-\.'/ !4 r\Erj_-n \:/-l MARTINSVILLE IGNEOUS COMPLEX

POLYMETAMORPHOSED ROCKS m ON THE SMITH RIVER ALLOCHTHON NOW AT GREENSCHIST FACIES

Figure 3. Regional geologic map showing metamorphic grade of rocks in south-central and southwestern Virginia. metamorphism high enough to produce minimum wackes, metagraywacke conglomerates, graphitic melt granites. Much of the Ashe is porphyroblastic, schists and pelitic schists. It also contains musco- with porphyroblasts ranging up to 6 cm across. vite-sericite schists, impure marbles, and quart- Some of these porphyroblasts are attenuated, flat- zites. With the exception of metabasalts, stratigra- tened, crinkle-folded and sheared (Michael B. phic horizon markers are not traceable over great McCollum, personal communication). At the con- distances. The metai gneous/metavolcan ic/metased- tact with the overlying rocks of the Alligator Back, imentary sequences appear to be repetitious. The the Ashe shows a flaggy foliation that is parallel Alligator Back ranges in metamorphic grade from to this contact. Mylonites also occur near this upper greenschist in the northeastern part of Area contact suggesting the possibility of post-metamor- I to lower and middle amphibolite grade in the phic thrusting of lower rank (greensehist and lower southwestern part (Figure 3). amphibolite grade) metamorphic rocks over higher rank (upper amphibolite grade) metamorphic M eta'igneous rocks: Extensive stratigraphic sequen- rocks within the Lynchburg Group. ces composed of metagabbro overlain by metabasalt occur throughout the Alligator Back. One Alligator Baek Formution of the most extensive of these sequences occurs at the base of the formation. Small bodies of meta- The Alligator Baek Formation contains metagabbro and ultramafic rock occur as lenses within morphosed ultramafic rocks, gabbros and basalts, the metasedimentary rocks (Plate). Three large and a clastic sequenee of interlayered metagray- bodies of metaigneous rocks underlie Grassy Hill, VIRGINIA DIVISION OF MINERAL RESOURCES

Jacks Mountain, and Brier Mountain, (Plate). All be amygdules; although amygdules are generally three bodies contain ultramafic rock and metagab- filled with calcite, epidote and quartz at this met- bro, and the outermost parts of the bodies generally amorphic grade. Also present are lens-shaped struc- contain metabasalt altered to amphibolite, indieat- tures that might represent transposed flow banding a close association among the ultramafic rocks, ing. Although those structures could be primary the metagabbros and the metabasalts. As pre- features, they are not definitive and could as easily viously noted, the Brier Mountain body is sur- be the products of metamorphism and tectonism. rounded by Ashe Formation, the body is here interpreted as being folded down into rather than Metased;imentary rocks: The metasedimentary being an intrusive body into the Ash Formation. rocks are locally interlayered with the metabasalts The ultramafie roeks are metamorphosed dunites near the top of the metaigneous sequences, but the and metapyroxenites that are generally altered to majority of the metasedimentary roeks stratigra- serpentine, chlorite, talc, and tremolite. These phically overlie the metabasalts. rocks locally contain relict olivine and pyroxene. The metagraywackes in the Alligator Back For- Opaque minerals occur in accessory amounts. Chlo- mation are composed of interbedded gray gneissic rite is commonly altered to vermiculite around the layers and muscovite-biotite schist layers. The margins of the ultramafic bodies. These bodies in gneissic layers are generally composed of 0.5-3 mm places are eut by metapyroxenite dikes and veins clasts of quartz and feldspar in a finer-grained, of anthophyllite. quartz-feldspar-mica matrix that in plaees grades The metagabbros are composed of actinolite (in upward into mica schist layers. The gneissic layers part uralitic amphibole), albite, epidote, chlorite, are variable in thickness and may locally be thick and minor amounts of zircon, quartz, sphene, il- and massive and contain very few sehist layers. menite, magnetite, and the relict minerals augite Elsewhere they occur as thin lenses and interbeds and calcic plagioclase partially altered to epidote. in mica schists and in graphite schists. At Town Some of the metagabbro is layered. The metagab- Creek, north of Henry, a metaconglomerate con- bro bodies are generally coarser grained and ligh- tains rock fragments up to 1 foot long (Henika, ter colored toward their centers and locally have 1971). The clasts are composed of granite, gneiss, relict ophitie textures. The metagabbros are locally and angular fragments of metaclaystones and gra- sheared and altered to aetinolite schist near con- phitie metaclaystones. Graded bedding is common. tacts. The basal bed of some graded cycles is a coarse, The metagabbros have not metamorphosed the structureless, polymictic conglomerate that grades country rocks with which they are in contact. upward into mica schist. In some exposures graded Although Conley and Henika (19?0) report a dense, beds are overlain by a thin interval of finely lam- gray hornfels-like rock at the top of the large inated, impure metasandstones that in turn are metagabbro body north of Fairy Stone State Park; overlain by thin, eross-bedded, mieaceous quart- examination by the writer of thin sections of this zites. These rocks are similar to units A through rock indicates that it is a highly indurated quart- C of a Bouma cycle, units common in proximal zite, rather than a hornfels. No growth of contact turbidite deposits near the mouth of submarine metamorphic minerals or development of hornfels canyons (Middleton and Hampton, 1973). Henika texture could be detected around the metagabbro. (1973) reports that large angular blocks of aetin- The metagabbros are cut by amphibolite dikes, olite gneiss (these, he speeulates were derived from which are probably feeders for the overlying met- metabasalt in the Lynchburg) oecur in the meta- abasalts. Magnetite deposits are associated with the graywackes. This would suggest that the Alligator metagabbros and have been mined for iron ore on Baek contains sedimentary melange sequences de- Stuarts Knob and west of Rocky Mount. rived in part from oeean-floor basalts. Dark-greenish-black basalts metamorphosed to The metagraywackes are eomposed of qaartz, well-foliated, fine-grained amphibolites generally microcline, perthite, plagioclase, muscovite and overlie the metagabbros and are in places inter- biotite and commonly contain small amounts (gen- layered with and overlain by metasedimentary erally + 5%) of epidote, sphene, ilmenite, ealcite, rocks. The amphibolites are composed primarily garnet, chlorite, zircon, and magnetite. Graphite of nematoblasts of actinolite and variable amounts oecurs sparingly throughout the metagraywackes of epidote, chlorite, albite and quartz. The meta- as disseminated material and as distinet graphite basalts are generally massive but locally contain sehist layers that generally lie on top of the met- small (1-2 mm) ovoid masses filled with intergrown agraywacke beds. qtnrtz and feldspar. It is possible that these could In the area around the nose of the Cooper Creek PUBLICATION 59

anticline, a sequence of silvery-gray, qtartz-miea the metagraywackes and in the graphite sehists. schist (and phyllite) interlayered with metagray- These quartzites are composed primarily of quartz, wacke forms a distinct mappable unit within the with lesser amounts of muscovite and biotite and Alligator Baek Formation. The base of this subunit accessory amounts of microcline, plagioclase, mag- is interlayered with the uppermost part of a se- netite, sphene, ilmenite, zitcon, and apatite. quence of metabasalts. The miea schist is eomposed Quartz-rich layers'are separated from each other of varying amounts of biotite, muscovite, and by thin sericite layers. Graphite-schist fragments qaartz. It commonly contains minor amounts of and biotite films are concentrated along foliation tourmaline, garnet, plagioclase, microeline, and surfaces. These quartzites are commonly composed ilmenite. The mica sehist also contains dissemin- of upward-fining packages that contain laminar ated graphite and thin graphite schist layers. and fine eross-bedded sequences. The writer has Graphite-bearing rocks ranging from graphite observed festoon cross-bedded, isoclinally folded schists to quartz- graphite schists occur throughout quartzite layers along the tracks of the Norfolk and the Alligator Back Formation. Thin graphite schist Southern Railway at Town Creek in the Philpott and quartz-graphite schist bands are interlayered Reservoir quadrangle. with the metagraywaekes. The graphitic schists are A fine-grained quartzite is in contact with, and gray to grayish-black and are composed of varying probably stratigraphically overlies, metagabbros amounts of quartz, muscovite, ehlorite, and graph- on the west shore of Fairy Stone Lake; a similar ite; lithologies range from a quartz-rich rock with quartzite also overlies metagabbros southwest of flaggy foliation to a miea-rich rock with well- Rocky Mount. These two quartzites are white to developed schistosity. These rock types are com- rusty yellow to light gray roeks composed mainly monly interlayered. The quartz-rieh graphite of saccharoidal quartz. Sphene is an accessory schists are composed of up to 50 percent quartz; mineral in the quartzites at Fairystone Lake, and the remainder consisis mainly of about equal magnetite is an accessory mineral in the quartzite amounts of graphite and muscovite. The more near Rocky Mount. Both quartzites are massive; schistose rocks have proportionately larger primary textures such as cross bedding, and relict amounts of muscovite and ehlorite. Accessory min- clasts are absent. They have a rude, laminar, non- erals include pyrite, ilmenite, and garnet; biotite penetrative foliation. These quartzites likely rep- may replace chlorite at higher metamorphic resent recrystallized eherts; the association with grades. igneous rocks would suggest that they might be The graphite schists were probably hemipelagic volcanic cherts. sediments deposited in a elosed basin under reduc- ing conditions as indicated by the presence of The I'anchburg Group, A Repetiti'ue graphite (preserved organic material) and pyrite. Sequence Of Ophi,oktes? And Th'eir Couer Rocks They probably represent sedimentation during times of quiescenee, whereas the metagraywackes Rankin (1975) has concluded that volcanic rocks were probably deposited by turbidity currents. in the Ashe Formation must have been deposited White, pinkish-orange and gray, fine- to coarse- in a marine environment and speculated that future grained marbles oecur interlayered with meta- workers may discover ophiolites in these roeks. The graywackes southeast of Rocky Mount (McCollum, stacked and repeated stratigraphic sequences con- in preparation), in the reentrantnorth of Dickenson sisting of altered ultramafic roeks overlain by (Conley, Piepul, Robinson, and Lemon, in prepa- metagabbros overlain by metabasalts, in turn over- ration), in the reentrant south and southwest of lain by a cover of metasedimentary rocks, within Sandy Level (Berquist, in preparation), and along the Alligator Back would suggest that these rocks Rennet Bag Creek and the Smith River west of represent ophiolites and their cover rocks that have Dodson (Conley and Henika, 1970). Most of the been repeated by thrusting (Conley, 198L and in marbles are finely laminated and contain thin, preparation). Some sequences contain ultramafic quartz-rich layers and numerous mica schist part- rocks, overlain by metagabbros, overlain by met- ings. One lens-shaped body of pinkish-white actin- abasalts; some contain metagabbros overlain by olite marble has been quarried in the Sandy Level metabasalts, whereas others contain only metaba- quadrangle. This marble is strikingly similar to salts. Sueh variations indicate that some sequences actinolite marble that occurs in the Lynchburg are complete, and others are truncated successions. rocks in the Sauratown Mountains anticlinorium In addition, a number of isolated lens-shaped near Danbury, North Carolina. masses of ultramafie-metagabbro + metabasalt are Impure micaceous quartzites form interlayers in enclosed by metasedimentary rocks. The angular VIRGINIA DIVISION OF MINERAL RESOURCES

fragments of metabasalt found by Henika (lg?1) ?- [. oceon-floor bosolls in the metasedimentary rocks near the base of the HPJ o Joponese lholeiites -i) O Howoiion lholeiites Alligator Back Formation in the Bassett quadran- oz I I a lslond orc ondesiles gle could be part of a melange sequence associated ff; fa o2 Lynchburg melogobbros with the beginning of obduction and emplacement S: 13 Lynchburg melobosolfs of the ophiolites.

Geochem'istry of Ophi,olites I oo& Ti ppm Work by Pearce and Cann (lg?1, 19?B) and ... o tt ' Pearce (1976) indicates that ocean-floor basalts, r?1. low-potassium tholeiites, calc-alkaline basalts, sho- .l' shonites, ocean island basalts and continental basalts can be distinguished from each other by ? element analysis. Ophiolites are chemically similar to ocean-floor basalts (Pearce and Cann, 1gZ1), AA oo2 A AA which supports the widely held theory that ophi- A

olites contain obducted ocean-floor basalts that 13 ol originated at spreading centers (Coleman, Lg77). To test the hypothesis that the ultramafic-met- 50 roo t50 agabbro-metabasalt sequences in the Lynchburg Zr gpm are ophiolites, samples from three metagabbros Figure 4.Ti-Zr plot for parental magma types. and four metabasalts were analyzed for major and trace elements. The elements Ti, Zr, and Y were chosen for analysis because these elements are not particularly mobile during low grade metamor- Ti /too

phism (Pearce and Cann, 19?3). Element analyses A Within glole bosotts for titanium were made by Oliver Fordham, B Colc-olkoline basotls M. C uw r tnoteiites Jr., Virginia Division of Mineral Resources. and D Oc€on floor bosolls analyses of the trace elements zirconium and yt- A3Lynchburg meiobosolts O2 Lyncnlurg melogobbros trium were made by David Whittington, Depart- ment of Geology, Florida State University. A comparison of Ti and Zr contents of the samples (Figure 4) shows that they all follow the trend of ocean-floor basalts, although sample numbered 1 and 3 are lower in Ti than samples plotted by Pearce c' and Cann (1971). A triangular diagram for Ti-Zr- f" x\ o Y (Figure 5) shows that two samples plot within the field of ocean-floor basalts and that five plot '/o"o' outside of this field but not in any of the other basalt fields. This is because of high yttrium content of the samples. Each of the five samples is, therefore, Yx3 much closer in composition to ocean-floor basalts Figure 5. Discrimination diagram for Ti, Zr, and than to other basalt fields in the diagram. Thus, Y. the stratigraphic and (to a lesser extent) ehemical data both tend to support the idea that these mafic igneous rocks are ophiolites. to the south of this latitude, rocks that reeord the 350-402 m.y. metamorphic event are exposed Metamorphic Age Datesfrom Roclcs of the Lgnchburg whereas, to the north ofthis latitude, rocks affected Group by this metamorphic event lie buried beneath roeks that record the older event. This would imply that Fullagar and Dietrich (1976) found that north rocks that reeord the later event have been over- of 36o52'N. latitude Rb/Sr age dates in the Lynch- thrust by rocks that record the earlier event and burg Group are 520 to 583 m.y.o. and are 3b0 to therefore have not yet been exposed at the surface 402 mry.o. south of this latitude. They propose that by uplift and erosion. Mose and Conley (1983) find PUBLICATION 59

that the rocks of the Cooper Creek anticline (north- mlca schist member ol tho Fo.k Mountian Formation western part of the map, Plate) at lower metamorphic grade (albite grade) yield Rb/Sr ages of 520- 580 m.y. and at higher metamorphic grade (oligoclase grade) give ages of about 350 m.y. As high rank metamorphism can reset dates recorded by low grade metamorphism, it is indeed likely that to the southwest along strike the Acadian orogeny was more intense and reset Taconic dates, whereas to the northeast along strike, it was less intense Figure 6. Stratigraphie relationships of rocks in and was unable to reset the older Taconic dates. the Smith River allochthon.

Candler Forrnation metavolcanic rocks eonsidered to be of Late Pre- In central Virginia, the Candler Formation over- cambrian or Early Paleozoic age and an Ordovician lies the continental basalts of the Catoetin Forma- age plutonie-igneous sequence that intrudes the tion, which uneonformably overlies the Lynchburg metasedimentary rocks (Rankin, 1975; Odom and Formation (Conley, 1978). In the area of study, Russell, 1975;Ragland, Conley and Odom, in prep- neither the top nor the bottom of the Candler is aration). exposed because this unit is in fault contact with Three episodes of metamorphism are recognized the Lynchburg Formation, both at its base and at in the metasedimentary rocks of the Smith River its top (Berquist, 1980). allochthon. The first episode was a regional Bar- The Candler is a medium- to dark-gray or dark- rovian-type metamorphism, which was followed by greenish-gray phyllite that is eomposed predom- regional, retrograde metamorphism either before inantly of serieite and chlorite and weathers to a or at the beginning of emplacement of the plutonic- pink and grayish-purple saprolite. Paragonite-rich igneous sequence of the Martinsville igneous eom- zones were defined in the unit in central Virginia plex. The third episode was contaet metamorphism by Smith, Miliei, and Greenberg (1964). Porphy- around plutons of the Martinsville igneous com- roblasts of magnetite and ehloritoid oceur locally. plex. The chloritoid porphyroblasts (up to 3 mm in Rocks of the Smith River allochthon have been diameter) are oriented across foliation (foliation correlated with rocks of the Inner Piedmont belt does not wrap around porphyroblasts) indicating of the Carolinas based on lithologic similarities and that the porphyroblasts are of post-tectonie origin. similar age dates of igneous roeks that intrude the Thin quartzite layers up to 3 cm thick occur locally allochthon and that intrude the Inner Piedmont belt in the unit. Thin sections reveal thin layers of (Conley and Toewe, 1968; Rankin, 1975; Odom and qaartz, only a single grain thick, interlayered with Russell 1975;Lemmon, 1980). Thusthe Smith River 1to 5 mm thick phyllite layers. The Candler loeally allochthon is interpreted as a klippe of the Inner contains very dark-gray layers. Investigations by Piedmont rocks that lies to the northwest of the Berquist (in preparation) and by the writer show rocks of the main Inner Piedmont belt. Therefore that this dark-gray color is generally because the it would seem logieal that rocks of the Inner presence of ehlorite rather than graphite. Piedmont belt were once part of a continuous sheet that extended as far westward as the Bowens Creek Anne rr: SMrrH RrvnR Alt ocsrnor't fault. Thus rocks now exposed in the Sauratown Mountains anticlinorium to the south and south- The Smith River alloehthon (Plate) was named west would have been covered by rocks of this Inner by Conley and Henika (1973). This allochthonous Piedmont thrust sheet, whieh have sinee been mass occupies a broad synform in the area between stripped off by erosion. How far westward beyond the Blue Ridge anticlinorium and the Sauratown the Bowens Creek fault this sheet might have Mountains anticlinorium. It is therefore inter- extended is not known. as these rocks have also preted that Lynchburg and Grenville basement been eroded away. rocks, which make up the Blue Ridge and Sau- ratown Mountains anticlinoria on either side of the Bassett Formation allochthon, also underlie the allochthon. The allochthon is eomposed of two sequences of rocks (Figure The Bassett Formation occupies several polyde- 6): a metasedimentary sequence containing some formed domes in the central and northwestern 10 VIRGINIA DIVISION OF MINERAL RESOURCES

parts of the Smith River allochthon. The Bassett the mapping is incomplete, present data suggest is the lowest struetural unit and probably the oldest that the amphibolite also thins to the southwest. stratigraphic unit in the allochthon and is subdi- The amphibolite is locally interlayered with the vided into a lower biotite gneiss and an upper upper part of the underlying biotite g:neiss, sug- amphibolite. Although more work is required, pre- gesting a conformable contact between the two liminary Rb-Sr data indicate a 1000 m.y. age for units. Amphibolite also oceurs as thin discontinuous the lower gneiss unit of the Bassett Formation layers in the overlying Fork Mountain Formation (Douglas Mose, written communication, 1984). indieating that volcanism continued after deposition of the biotite gneiss of the Bassett Formation. Biot'ite gne,iss: The biotite gneiss that makes up the The amphibolite is a grayish-black to greenish- lower part of the Bassett is a fairly homogeneous black, foliated, medium- to coarse-grained rock. In unit of generally equigranular, medium-grained, areas of relatively high metamorphic grade, such light- to medium-gray rock eomposed of biotite-rieh as exposures along State Highway 57 on the south- laminae, about 0.6 cm thick, interlayered with I western city limits of Bassett, it contains relic to 3-cm-thick laminae that contain less biotite. In orthopyroxene and is segregated into feldspar-rich addition, massive biotite gneiss layers (up to 0.b and amphibole-rich layers cut by thin, feldspar- m thiek), quartz-rich (50 percent quartz), and rich dikes that outline ptygmatic folds (Figure 6). epidote quartzite layers occur sparingly in the unit. The amphibolite is composed predominantly of At places where high metamorphic grade was hornblende and plagioclase. Ovoid masses of pla- attained during either regional or contact meta- gioclase, epidote, and quartz that resemble flat- morphism, the rock reached minimum melt con- tened amygdules occur in the unit southwest of the ditions and locally contains microcline porphyrob- town of Bassett, and beds of epidosite, up to two lasts, migmatite zones, and coarse mica-quartz- feet thick, also occur in the amphibolite in this same feldspar melt zones. In such areas the rock is cut area. The amphibolite at the top of the Bassett by numerous quartz-feldspar and mica-qaartz- Formation contains features that resemble graded feldspar pegmatite dikes. bedding and eut-and-fill struetures (Conley and Altered pods and stringers of ultramafie rock Henika, 1970). Major element analyses indicate and thin metagabbro bodies occur in the biotite that eompositions are similar to that of continental gneiss, especially along the western boundary of basalts (Paul C. Ragland, written communication, the allochthon. The ultramafic rocks are predom- 1979). Achaibar and Misra (1984) also have con- inantly altered to talc, tremolite, ehlorite, serpen- cluded that these basalts were emplaced in a rift tine, anthophyllite, opaque minerals and vermic- environment. However, these rocks have been met- ulite but may contain relict olivine and pyroxene. amorphosed at amphibolite grade and, because of Some of these ultramafic bodies have an outer shell mobility of many of the elements at this grade, the composed of coarse amphibolite. The metagabbros eorrelation of these rocks with continental basalts are associated with the ultramafic rocks and occur is extremely questionable (Paul C. Ragland, p€r- primarily in the northwestern part of the alloeh- sonal communication). thon. They are generally thin, conformable pods and sill-like bodies composed of clinopyroxene, orthopyroxene, garnet, hornblende and plagioclase. Fork Mountain Formatian A striking feature of some of the metagabbros is that the garnets are surrounded by thin coronas The Fork Mountain Formation is composed of composed of plagioclase and symplectic inter- two units, a mica schist and a biotite gneiss that growths of plagioclase-pyroxene. Mafic and ultra- could be in part laterally equivalent to each other. mafie rocks are rare in the biotite gneiss in the The biotite gneiss is the basal unit of the Fork southeastern part of the mapped area. Mountain Formation in the southeastern part of the Smith River allochthon (Plate and Figure 6) Am,pbibolite: The top of the Bassett is generally and apparently wedges out to the northwest be- composed of amphibolite. The amphibolite is at, neath the mica schist. Therefore, the mica schist or near, its maximum thickness in the west-central overlies the Bassett Formation along the northwest- part of the mapped part of the allochthon (Plate) ern boundary of the allochton and the biotite gneiss and thins to the southeast. In the central and overlies the Bassett Formation to the southeast. southeastern part of the mapped area, it occurs in Contacts between these two units appear to be thin, discontinuous stringers, and farther to the gradational or intertonguing over relatively short southeast in the map area it is absent. Although distances. These gradational relationships led Con- PUBLICATION 59 11

ley and Toewe (1968) to propose that the gneiss The miea schist eontains some gneissic layers and resulted from contact metamorphism and metaso- lens-shaped, quartz-rich and mica-rich interlayers matic replacement of the miea sehist. This sugges- that could be primary compositional beds, which tion was based on observations that were limited have been tectonically transposed. High-alumina to areas where the Fork Mountain had been in- minerals generally are confined to mica-rich layers. truded by the Martinsville igneous eomplex and The quartz in the quartz-rich layers oecurs as not on areas that were mapped later in the project polygonal aggregates strongly suggesting that it which had not been affected by contact metamor- has been annealed. Light- to dark-gray, fine- phism. More recent mapping in the area (Price and grained, equigranular quartzite, in lenses a few others, 19804 and 19808) indicates that the biotite hundred meters wide and generally a few meters gneiss unit is not restricted to contact zones of the thick, occurs locally in the mica schist. Martinsville igneous complex and is indeed a stra- The mica sehist is composed of museovite, quartz, tigraphic unit. garnet, and high-alumina minerals with accessory amounts of plagioelase, magretite and titanium- Mina Schisfi The mica schist is a light- to medium- bearing minerals. Euhedral garnets are ubiquitous gray, porphyroblastic, fine- to medium-grained, in the mica sehist unit, but southeast of the relict high-alumina metapelite. The high-alumina com- sillimanite isograd they occur as globular-shaped position of this roek makes it an exeellent indicator aggregates, which may have grown together to of metamorphic grade. The mineraloga is variable form almost continuous garnet bands. The staur- and dependent on grade of regional metamorphism, olite crystals that formed during regional meta- on the amount of alteration that has oecurred morphism west of the sillimanite isograd are large during subsequent retrograde metamorphism, and (1-7 cm), typically amber in color, generally finally on the grade obtained during the last contact twinned and partially to totally altered to sericite metamorphism. Contact metamorphism is res- pseudomorphs. Biotite occurs in the mica schist, tricted to the area adjacent to the plutons of the but to the southeast of the sillimanite isograd it Martinsville igneous eomplex. is almost universally altered to chlorite. The miea sehist is mappable as two units sep- Contaet metamorphic aureoles (Figure 3) sur- arated on the basis of metamorphic grade obtained rounding the plutons of the Martinsville igneous during the first regional metamorphic event (Plate, complex have greatly affected the mineraloga of Figure 3). These two units are: garnet-miea schist the mica schist for distances up to 200 feet (61 m). containing relict staurolite, which lies northwest Near the contaet, the rock has recrystallized under of the staurolite-sillimanite isograd alongthe north- statie metamorphic eonditions that caused growth western boundary of the Smith River allochthon; of unoriented micas, which produced a fels texture and garnet-miea sehist containing relict silliman- and obliterated the previously developed schistosity ite, which lies to the southeast of this isograd. (Fieure 7). Masses of sillimanite (variety fibrolite), partially The contact with the plutonie roeks is marked altered to sericite, occur southeast of the sillimanite by mica-quartz-microeline migmatite layers and isograd. Some of this sillimanite is pseudomorphous cross-eutting pegmatites, all probably derived from after staurolite and eontains poikiloblastic inelu- anatectie melting. Coarse sillimanite porphyrob- sions of quartz and garnet inherited from the lasts oceur in the migmatite zone and are prog:res- staurolite. This observation suggests that regional sively replaced away from the contact by fibrolite; metamorphie grade increased to the southeast, and fine-grained kyanite; and microseopic, untwinned that staurolite was replaced by sillimanite in that staurolite porphyroblasts. Thin sections show that direction within the allocthon. In areas southwest these high-alumina minerals have nucleated and of the Smith River allocthon, Rankin, Espenshade, grown in lens-shaped masses of sericite that occur and Shaw, (1973) report that the contact between in a quartz-mica matrix (Figure 7). The serieite rocks containing relict staurolite and those contain- masses are interpreted as areas previouslyoccupied ing relict sillimanite represents a thrust fault. This by high-alumina minerals (either large sillimanite fault thrust the sillimanite-bearing rocks westward masses or large staurolite porphyroblasts). These over staurolite bearing roeks. Ifso, this thrust fault porphyroblasts formed during regional metamor- probably does not extend into the present study phism (M) and were retrograded to sericite during area beeause the previously eited data indieate that a second metamorphic event (Mz) which occurred in this area the boundary between the staurolite either at the beginning of, or prior to, intrusion and sillimanite schists is a relict metamorphic of the Martinsville igneous complex and develop- isograd. ment of its thermal aureole (M). Such sericite t2 VIRGINIA DIVISION OF MINERAL RESOURCES

Emery and magnetite deposits have also been locally developed in the contact aureole between the gabbros of the Martinsville igneous complex and the high-alumina schists of the Fork Mountain Formation (Conley and Toewe, 1968; Conley and Henika, 1973). The emery is a dark-gray, non- foliated rock composed of interlocking green spinel (pleonaste or hercynite) and magnetite crystals, which envelop crystals of corundum (Conley and Henika, 1973).

B'iot'i,te gneiss: The biotite gneiss of the Fork Moun- tain Formation is a medium-gray, compositionally banded rock that is composed of interlayered quartzo-feldspathic gneiss and garnetiferous muscovite-biotite gneiss. The biotite gneiss contains about equal amounts of qtartz (Locally the quartz grains may have a blue color, caused by microscopic rutile inclusions) and plagioclase and varying amounts of biotite, microcline, garnet, muscovite, and high-alumina minerals. Opaque minerals, garnet, and high-alumina minerals occur primarily in the biotite-rich layers; whereas, the quartzo- feldspathic layers are composed predominantly of qtartz, plagioclase, microcline and minor amounts Figure 7. Mica schist member of the Fork Mountain of biotite and muscovite. The interlayering of Formation from the contact metamorphic aureole quartzo-feldspathic and mica-rich bands is thought around the Martinsville igneous complex. Large to reflect original compositions of the sediments white areas are pseudomorphic forms of staurolite from which they were derived: the mica-rich layers crystals that grew during regional metamorphism were probably more pelitic in composition and the (M1), now replaced by aggregates of coarse, un- quartzo-feldspathic layers were probably of gray- oriented sillimanite porphyroblasts that grew dur- wacke composition. ing contact metamorphism (M"). Note that the Clinozoisite-rich, quartzite boudins a few cen- matrix of the rock is completely iecrystallized and timeters thick are scattered throughout the unit, has developed a fels texture, which has replaced and probably represent original carbonate-rich the original schistose texture of the rock. sandstone beds. Lithic, matrix supported breccias composed of biotite gneiss quartzites and quartz- rich gneiss fragments up to 45 cm across were found masses (formed during Mr) are rich in alumina and in the Martinsville stone quarry south of Fieldale are favored sites for formation of new high-alumina (Figure 8) and along a small stream which flows minerals. across the Colonel Lester Farm near the southwest- As here noted, it has not been conclusively de- ern terminus of Turkeycock Mountain (Figure 9). termined when M, occurred in relationship to the Some of the clasts seem to be identical in compo- intrusion of the Martinsville igneous complex. It sition to those of the matrix, others are quartz-rich could have occurred either prior to or at the be- gneisses and some are fragments of quartzite. The ginning of emplacement of the igneous complex. foliation observed in the clasts is not parallel to This metamorphism might have occurred as a the penetrative foliation developed in the matrix, result of water migration from the plutons into the indicating that foliation was present in the clasts country rock during the initial stages of emplace- prior to their deposition. This is further substan- ment of the igneous complex before the develop- tiated by the fact that the foliation in the matrix ment of a thermal aureole that resulted in contact is a regional feature that is parallel to compositional metamorphism (Mg). Recent work by Allison and layering, indicating that bedding has been trans- others (1984) shows that the gabbroic magma of posed into parallelism with the penetrative folia- the Rich Acres Formation was water saturated tion. Rankin (1975) has compared those rocks to during crystallization. the diamictite facies of the Wissahickon Formation t2 VIRGINIA DIVISION OF MINERAL RESOURCES

Bioti.te gneiss: The biotite gneiss of the Fork Moun- tain Formation is a medium-gray, compositionally banded rock that is composed of interlayered quartzo-feldspathic gneiss and garnetiferous muscovite-biotite gneiss. The biotite gneiss contains about equal amounts of qtartz (Locally the quartz grains may have a blue color, caused by microscopic rutile inclusions) and plagioclase and varying amounts of biotite, microcline, garnet, muscovite, and high-alumina minerals. Opaque minerals, garnet, and high-alumina minerals occur primarily in the biotite-rich layers; whereas, the quartzo- feldspathic layers are composed predominantly of qtartz, plagioclase, mierocline and minor amounts Figure 7. Mica schist member of the Fork Mountain of biotite and muscovite. The interlayering of Formation from the contact metamorphic aureole quartzo-feldspathic and mica-rich bands is thought around the Martinsville igneous complex. Large to reflect original compositions of the sediments white areas are pseudomorphic forms of staurolite from which they were derived: the mica-rich layers crystals that grew during regional metamorphism were probably more pelitic in composition and the (M1), now replaced by aggregates of coarse, un- quartzo-feldspathic layers were probably of gray- oriented sillimanite porphyroblasts that grew dur- wacke composition. ing contact metamorphism (Ms). Note that the Clinozoisite-rich, quartzite boudins a few cen- matrix of ttre rock is completely recrystallized and timeters thick are scattered throughout the unit, has developed a fels texture, which has replaced and probably represent original carbonate-rich the original schistose texture of the rock. sandstone beds. Lithic, matrix supported breccias composed of biotite gneiss quartzites and quartz- rich gneiss fragments up to 45 cm across were found masses (formed during Mo) are rich in alumina and in the Martinsville stone quarry south of Fieldale are favored sites for formation of new high-alumina (Figure 8) and along a small stream which flows minerals. across the Colonel Lester Farm near the southwest- As here noted, it has not been conclusively de- ern terminus of Turkeycock Mountain (Figure 9). termined when M, occurred in relationship to the Some of the clasts seem to be identical in compo- intrusion of the Martinsville igneous complex. It sition to those of the matrix, others are quartz-rich could have occurred either prior to or at the be- gneisses and some are fragments of quartzite. The ginning of emplacement of the igneous complex. foliation observed in the clasts is not parallel to This metamorphism rnight have occurred as a the penetrative foliation developed in the matrix, result of water migration from the plutons into the indicating that foliation was present in the clasts country rock during the initial stages of emplace- prior to their deposition. This is further substan- ment of the igneous complex before the develop- tiated by the fact that the foliation in the matrix ment of a thermal aureole that resulted in contact is a regional feature that is parallel to compositional metamorphism (Ms). Recent work by Allison and layering, indicating that bedding has been trans- others (1984) shows that the gabbroic magma of posed into parallelism with the penetrative folia- the Rich Acres Formation was water saturated tion. Rankin (1975) has compared those rocks to during crystallization. the diamictite facies of the Wissahickon Formation PUBLICATION 59 13

par porphyroblasts that are not developed away from the contact. The garnets in the interlayers of garnetiferous muscovite-biotite gneiss have grown together into globular masses (as they did in the mica schist); also, coarse sillimanite is developed in the pelitic layers near contacts with rocks of the igneous complex, whereas fine-grained kyanite and microscopic staurolite formed in these layers away from the contacts.

Martinsville Igneous ComPlex

The Martinsville igneous complex was infor- mally named by Ragland (1974). The igneous complex underlies a large area around Martinsville Figure 8. Biotite gneiss of the Fork Mountain (Plate); isolated plutons also occur to the east of Formation from the Martinsville Stone Company the main outcrop area. The complex is composed quarry south of Fieldale containing angular frag- of three formations (Figure 6), the Leatherwood ments of calc-silicate quartzite. Pencil in the center Granite (Jonas, 1928), the Rich Acres Formation of the photograph is for scale. (Conley and Henika, 1973) and norite. The norite was earlier included as part of the Rich Acres Formation (Conley and Toewe 1968; Conley and Henika, 1973). However, later work (Allison and others 1984; Ragland, Conley and Odom, in preparation) indicates that the norite is separate from, and younger than the Rich Acres and the Leather- wood. Analyses of strontium isotopes indicate that the Rich Acres and Leatherwood were derived from the same magma and were emplaced toward the end of a tectonic event (Ragland, Conley and Odom, in preparation). These two cogenetic rock units form an uncommon, high-potassium, calc-alkaline (Andean) plutonic sequence in which there was simultaneous fractionation of biotite and pyroxene indicating a high water content of the magma during crystallization (Allison and others, 1984). Radiometric age dates from the Leatherwood Gran- Figure 9. Biotite gneiss of the Fork Mountain ite (U/Pb, zircons and Rb/Sr whole-rock analyses) Formation exposed on the Colonel Lester Farm show that it is Middle Ordovician in age (Rankin near the southwestern terminus of Turkeycock 1975; Odom and Russell, 19?5) and because it is Mountain. The rock contains angular fragments sheared, it was probably emplaced and cooled and blocks of biotite gneiss and quartzite in a biotite during a tectonic (Taconic?) event. The norite was gneiss matrix. The coin (quarter) in the center of derived from a separate magma and lack of shear- the photograph is for scale. ing indicates that it was emplaced later, in a post- tectonic environment (Allison and others, 1984; Ragland, Conley and Odom, in preparation). (Conowingo Gneiss), which is considered to be submarine slide breccia or slump deposit. Debris Rich Acres For'fiLation flows can also produce this type of deposit (Walker, 1978). The Rich Acres Formation generally occurs ari The biotite gneiss in the metamorphic aureole concordant to slightly discordant plutons, whictr developed adjacent to the rocks of the Martinsville intrude the metasedimentary rocks of the alloch- igneous complex is injected by cross-cutting peg- thon. This formation makes up the major part of matites and contains migmatitic bands. Gneisses the complex and its major outcrop area is located at the contact with the igneous rocks contain felds- east and southeast of Martinsville. The rock is dark- PUBLICATION 59 13

Martinsville Igneous Complex

The Martinsville igneous complex was infor- mally named by Ragland (1974). The igneous complex underlies a large area around Martinsville Figure 8. Biotite gneiss of the Fork Mountain (Plate); isolated plutons also occur to the east of Formation from the Martinsville Stone Company the main outcrop area. The complex is composed quarry south of Fieldale containing angular frag- of three formations (Figure 6), the Leatherwood ments of calc-silicate quartzite. Pencil in the center Granite (Jonas, 1928), the Rich Acres Formation of the photograph is for scale. (Conley and Henika, 1973) and norite. The norite was earlier included as part of the Rich Acres Formation (Conley and Toewe 1968; Conley and Henika, 1973). However, later work (Allison and others 1984; Ragland, Conley and Odom, in preparation) indicates that the norite is separate from, and younger than the Rich Acres and the Leather- wood. Analyses of strontium isotopes indicate that the Rich Acres and Leatherwood were derived from the same magma and were emplaced toward the end of a tectonic event (Ragland, Conley and Odom, in preparation). These two cogenetic rock units form an uncommon, high-potassium, calc-alkaline (Andean) plutonic sequence in which there was simultaneous fractionation of biotite and pyroxene indicating a high water content of the magma during crystallization (Allison and others, 1984). Radiometric age dates from the Leatherwood Gran- Figure 9. Biotite gneiss of the Fork Mountain ite (U/Pb, zircons and Rb/Sr whole-rock analyses) Formation exposed on the Colonel Lester Farm show that it is Middle Ordovician in age (Rankin near the southwestern terminus of Turkeycock 1975; Odom and Russell, 1975) and because it is Mountain. The rock contains angular fragments sheared, it was probably emplaced and cooled and blocks of biotite gneiss and quartzite in a biotite during a tectonic (Taconic?) event. The norite was gneiss matrix. The coin (quarter) in the center of derived from a separate magma and lack of shear- the photograph is for scale. ing indicates that it was emplaced later, in a post- tectonic environment (Allison and others, 1984; Ragland, Conley and Odom, in preparation). (Conowingo Gneiss), which is considered to be submarine slide breccia or slump deposit. Debris R'ich Acres Fmmation flows can also produce this type of deposit (Walker, 1978). The Rich Acres Formation generally occurs as The biotite gneiss in the metamorphic aureole concordant to slightly discordant plutons, which developed adjacent to the rocks of the Martinsville intrude the metasedimentary rocks of the alloch- igneous complex is injected by cross-cutting peg- thon. This formation makes up the major part of matites and contains migmatitic bands. Gneisses the complex and its major outcrop area is located at the contact with the igneous rocks contain felds- east and southeast of Martinsville. The rock is dark- L4 VIRGINIA DIVISION OF MINERAL RESOURCES

greenish-gray and has an ophitic to subophitic The Leatherwood is a porphyritic, light-gray texture. It has a medium grain size, but is locally granite that generally shows rapakivi texture. How- porphyritic and contains stubby plagioclase phe- ever, some of the larger plutons are composed of noerysts that range up to l.b cm in length. These coarse, equigranular, leueocratic granite. Micro- phenocrysts contain numerous minute unidentified cline phenocrysts range from2-5 em and are gen- inclusions. The rocks of the formation have chem- erally white but locally may be pink. Some spec- ical compositions on the borderline between gabbro imens contain oligoclase as well as microcline and diorite (Paul C. Ragland, personal communi- phenocrysts. The phenocrysts are set in a medium- cation). They are composed of the minerals plagi- grained xenomorphic-granular matrix composed oclase, green hornblende, reddish-brown biotite, of microcline, quartz, plagioclase, biotite and mus- pale-green clinopyroxene, uralite, and quartz as covite. vermicular intergrowths in hornblende and plagi- Post-magmatic processes of diffusion and unmix- oclase. ing in the Leatherwood are indicated by rapakivi Rocks of the Rieh Acres Formation have large texture and patch antiperthites. The perimeters of (2em) clinopyroxene crystals filling the interstices the microelines have been embayed by post-rapa- between feldspars. Hornblende occurs as reaction kivi lobes of myrmekitic albite which replaees both rims on pyroxene and as subhedral crystals in the the albite rims and the microcline eores. The Lea- matrix. Biotite is in contact with hornblende and therwood locally contains blue quartz (as do some either is in contact with, or contains inclusions of of the gneisses in the aureole around the Martins- opaque minerals. Uralite embays and has partially ville igneous complex) which probably means that to totally replaced clinopyroxene and hornblende. submicroscopic rutile exsolved from quartz lattiees Development of vermiform quartz within horn- after crystallization (Mason, 1978). blende grains seems to have occurred after the The granite locally shows cataclastic textures. partial replacement of hornblende by biotite, as Formerly large quartz grains now oceur as un- biotite does not contain these quartz inclusions. strained, recrystallized polygonal aggregates that Although the rock is not obviously sheared, some show well-developed triple points. The epitaxial of the plagioclase grains are bent and the outlines albite and the host mierocline phenocrysts may not of some grain boundaries and twin planes are offset now be optieally continuous, and the albite may by shear planes. now consist of a thin band composed of an equi- The Rich Acres Formation is brecciated at the granular aggregate of recrystallized grains. In perimeters of some plutons, and fractures are filled some granite specimens distinct shear planes ean with injected material to produce agmatite texture. be observed; in these shear planes the micas are The injected material is coarser grained than the aligned and wrap around feldspar phenocrysts. ground mass of the brecciated material. but much These data would suggest that tectonism continued of the injected material is chemically (paul C. after cnystallization of the Leatherwood. In eon- Ragland, personal communication) and mineralog- trast, the myrmekitic albite whieh embays both the ically similar to the brecciated rock. This indicates albite rims and microcline cores is not sheared and that little differentiation of the parent magma took recrystallized, suggesting that it formed in a post place between the time of crystallization of the host tectonic environment. rock and the time of injection of the material filling Muscovite-quartz-microcline pegmatites of two the fractures. The outer parts of some plutons are ages cut the Rich Acres and the Leatherwood injected with thin veins composed of hornblende- formations. One of these groups of pegmatites is plagioclase and hornblende-pyroxene-plagioclase, slightly sheared (as is the Leatherwood) and the and with quartz-microcline-oligoclase pegmatites. other is unsheared and is considered to be younger than the Leatherwood. Leatherwood Qranite A U/Pb age of 450 m.y. from zircons (Rankin, 1975) and a whole-rock Rb/Sr age of 464+ 29 The Leatherwood Granite occurs as dikes, sill- is reported by Odom and Russell (1975) for^.t. the like bodies and irregularly-shaped plutons. The Leatherwood Granite. Odom and Russell (1975) and major part of the Leatherwood occurs as thin sheets Rankin (1975) have noted that these ages agree with on top of the large pluton of Rich Acres that lies dates obtained from intrusive roeks in the Inner east and southeast of Martinsville. In the northern Piedmont belt, which supports the suggestion of and northeastern parts of the allochthon, the Lea- Conley and Toewe (1968) that rocks of the Smith therwood occurs in oval-shaped plutons that are River allochthon correlate with rocks of the Inner diapir-like intrusions. Piedmont belt. A previously published U/Pb date PUBLICATION 59 l5

of 1020 m.y. obtained from the Leatherwood Gran- The norite does not contain the bent feldspar ite (Conley and Henika, 1973) is here eonsidered crystals with displaeed twin planes seen in the Rieh to be incorrect because of error in analyses on which Acres Formation, nor the sheared grain boundaries this date is based. observed in the Leatherwood. This suggests that the norite is a post-tectonie intrusive rock. Unnamed Nwite Anpe III: SAURATOWN MOUNTAINS An unnamed norite makes up a smaller propor- ANucuNonruu tion of the Martinsville igneous complex than do either the Rich Acres Formation or the Leather- In the Sauratown Mountains anticlinorium (Fig- wood Granite. It occurs as small, irregularly- ure 10), Grenville-age basement rocks are overlain shaped plutons and possibly as dikes. The exaet by Late Precambrian metasedimentary roeks. shape ofthese plutons is hard to discern in saprolite Rocks of the Sauratown Mountains anticlinorium because of similar weathering characteristics of the (Plate) are bounded on the north and northwest Rich Acres and the norite. by the Ridgeway fault, the southeastern boundary The norite is a dark-gray porphyritie rock in fault of the Smith River alloehthon, and on the which large (1-4 cm) pyroxene and elongate pla- southeast by the Chatham fault, the border fault gioclase crystals (up to 1 cm in length) produce of the Danville Triassic basin. an ophitic texture. The rock is composed of plagioelase (bytownite-labradorite), orthopyroxene Stuart Creek Gne'i,ss (predominantly hypersthene), clinopyroxene, brown pargasite, brown biotite, green hornblende The oldest unit in the Sauratown Mountains (uralite) and olivine. Rims of partial reaction anticlinorium in Virginia is a granitic augen gneiss around nuelei of olivine indicate the order of crys- that occupies the cores of four structural domes tallization, which is: olivine - orthopyroxene - eli- in the area. This rock is correlated with the Elk nopyroxene - pargasite - biotite. Green uralitic Park Group of Southwestern Virginia and north hornblende also forms as reaction rims on parga- central North Carolina by Espenshade and others site. Some plagioclase laths are embayed by ortho- (1975), who suggest that it "might be a porphyritic pyroxene indicating that their crystallization be- variety of Cranbemy Gneiss," which is a part of gan before eompletion of orthopyroxene growth. the Elk Park Group. The granitic augen gneiss is

TOP OF SECTION NOT EXPOSED

gornclifcrour murcovifc-biolitc schisl

lorkific aronitc

nuou3 lorar gornclifrrous

Sfuorl Crcck Gncics

Figure 10. Stratigraphic relationships of rocks in the Sauratown Mountains anticlinorium. 16 VIRGINIA DIVISION OF MINERAL RESOURCES a widespread, distinctive, and uniform rock unit posed in the Blue Ridge anticlinorium. The over- that is here named the Stuart Creek Gneiss. Its lying sehist eontains very few alternating gneiss- type locality is designated as exposures along both schist sequences but does contain marbles, quart- sides of Stuart Creek from where State Road 632 zites, metabasalts and ultramafic rocks typieal of crosses Stuart Creek. northwestward for a distance the Alligator Back Formation. Espenshade and of 2 miles. The area of the type locality is within others (19?5) did not recognize the Alligator Back the Spray 7.5 minute-quadrangle, Henry County. Formation in the Sauratown Mountains anticli- The Stuart Creek Gneiss is a porphyroblastic norium. However, in the writers opinion these rocks orthogneiss composed of euhedral and subhedral in the schistunit are more similar to Alligator Back porphyroblasts of microcline (relict phenocrysts?) than they are to the Ashe Formation. and perthite in a quartz-feldspar-biotite matrix, which generally lacks compositional banding. The Ashe Formation rock ranges in texture from porphyroblastic gneiss to augen gneiss, to flaser gneiss. Flaser gneiss is The amphibolite at the base of the Ashe Forma- generally in the sheared, upper part of the unit, tion exposed in the Sauratown Mountains anti- near and at its eontact with overlying, younger clinorium pinehes and swells and in places is totally metasedimentary rocks. Thin amphibole schist and absent. Therefore, the gneiss member of the Ashe biotite schist layers have been observed in saprolite; locally rests directly on the Stuart Creek Gneiss these might represent mafic igneous intrusions into with no intervening amphibolite unit. This basal the Stuart Creek that have been altered during amphibolite is a dark-green to greenish-black, gen- metamorphism. erally schistose to well-foliated, medium- to coarse- The Stuart Creek Gneiss is thought to be of grained rock. It is composed predominantly of Grenville age. Rocks in a similar stratigraphic hornblende and subordinate plagioclase. The roek position below a metasedimentary cover in a quarry also contains garnet, as well as aecessory amounts located about 25 miles to the southwest at Pilot of sphene, epidote, and opaque minerals. Mountain, North Carolina are cut by granitic rocks The gneiss unit which overlies the amphibolite which were dated atll92 m.y. (Rankin and others, makes up the major part of the Ashe Formation 1971). The rocks in this quarry, however, appear in the Sauratown Mountains anticlinorium. It is to be compositionally layered gneisses, unlike the a muscovite-biotite gneiss that eontains many in- porphyroblastic Stuart Creek Gneiss. terlayers of museovite-biotite schist. In the area east of Ridgeway, pods and stratiform bodies of Lynchburg Group ultramafic rocks are interspersed throughout the unit. Pegmatite and alaskite dikes and sills are The Stuart Creek Gneiss is unconformably over- common in the unit. lain by a sequence of metasedimentary rocks of Gneissic layers range from 2 to 10 feet thick and probable Late Preeambrian age. These roeks are the intervening schist layers are generally less than subdivided into two major units, a gneiss and an a foot thick. The gneiss is medium-grained, light- overlying schist. Amphibolites occur discontinu- gray and composed of miea plates interspersed with ously at the base of the gneiss unit and amphibolites elongate grains of quartz and feldspar. The rock and ultramafie rocks occur at the base of the is composed of approximately 60 percent feldspar, overlying schist unit. These metasedimentary rocks and plagioclase is predominant over microcline. have been correlated with the Lynchburg Forma- Quartz ranges from 20 to 30 percent and biotite tion (Lynehburg Group of this report) (Conley and ranges from 10 to 20 percent of the rock. Muscovite Henika, 1973). They have also been mapped as the is variable and ranges from traee amounts to 10 Ashe Formation (the lower formation of the Lynch- percent in the gneissic layers and eomposes almost burg Group as defined in this report) by Espen- all of the mica schist layers. The rock also eontains shade and others (1975). Because ofthe intervening minor amounts of tourmaline, zircon, sphene, ru- Smith River allochthon, rocks of the Lynchburg tile, epidote, and opaque minerals. Group are not physically traceable into these rocks. However, from lithologic similarities and stratigra- Alligator Banlt Formation phic relationships, these rocks are considered by Espenshade and others (1975) to be the Ashe For- The amphibolite atthe base of the Alligator Back mation that lies southeast of the allochthon. The Formation, where present, is a marker horizon that lower unit of the sequence, the gneiss unit, is very separates the Allisator Back from the underlying similar lithologically to the Ashe Formation ex- Ashe Formation. This unit is a massive to conspic- PUBLICATION 59 t7 uously foliated greenish-black "salt and pepper" group in Connecticut (Olsen and others, 1978). This rock. The major constituent is bluish-green horn- correlation is based on fossil fish and phytosaurs. blende with lesser amounts of garnet, plagioelase The Danville basin is a northeast-trending struc- and quartz. The amphibolite locally contains oval- ture that is about 123 miles long (Figure 2). The shaped masses of epidote and epidote-quartz up to basin (Plate) is bounded on the northwest by the 7 mm long that resemble flattened amygdules. Chatham fault (Myertons, 1963). At the southeast- Lens-shaped masses of fine- to medium-grained ern margin of the basin the sedimentary rocks may granite gneiss composed of microcline, oligoclase be either in unconformable or fault contact with and quartz with accessory hornblende, garnet, metamorphic roeks (Myertons, fgffi). Strike of sphene and zireon occur in the amphibolite unit bedding within the basin generally is parallel to at the base of the Alligator Back. This amphibolite the trend of the Chatham fault zone and the roeks also contains several lenticular masses of metapy- have a rather consistent N44oW dip, except near roxenite that seem to be at or near its base. The the Chatham fault, where dips are steeper (Thayer, metapyroxenite is altered to talc, serpentine, chlor- 'in Henika, L977\. Estimated thiekness of strata in ite, magnetite and tremolite. Large (1-3 cm) py- the Danville basin, calculated from outcrop width roxene phenocrysts generally occur in the metapy- and average dips, ranges from 3600 feet in the roxenite and are partially to totally altered to narrowest part of the basin to 13,300 in the widest pseudomorphous talc. Loeally there are isolated part (Henika and Thayer, 1980). The rocks are lenses of amphibolite that are entirely surrounded dusky red, yellowish-gray and medium-dark gray by the Ashe Formation (Price and others, 1980A, and show abrupt vertical and lateral changes in 19808). These may represent synclinal folds of the texture, color, composition and thickness. basal amphibolite of the Alligator Baek in the Within the present study area the Danville basin underlying Ashe Formation. was mapped by Paul A. Thayer (Thayer, 'inHenika, The amphibolite is overlain by a schistunit which 1977; Thayet, 'in Price and others, 1980A and makes up the major part of the Alligator Back 19808; and Henika and Thayer, 1980). Myertons Formation. This unit is a light-bluish-gray mus- (1963) thought that rocks of the Danville basin were covite-biotite schist containing abundant garnets an intertonguing sedimentary sequence and were and locally may contain thin layers of graphitic roughly equivalent in time to each other. He be- mica schist and layers of quartzo-feldspathic lieved that these roeks are uneonformably overlain gneiss. The schist is composed of muscovite, brown by a conglomerate that occurs on either side of the biotite, quartz and minor plagioclase; in addition basin, which he named the Cedar Forest Formation it contains varying amounts of kyanite and stau- (Figure 4). Thayer (1970) revised Myertons (1963) rolite. interpretation of the stratigraphy of the basin Garnets in the schist are generally euhedral, pink (Figure 11) and concluded that, in the southwestern to red, and range in size from 1 to 4mm. Poiki- and northeastern parts of the basin, the upper loblastie inclusions in the garnet porphyroblasts elastic sequence, which he named the Stoneville observed in thin sections indicate syntectonie ro- Formation could be separated from the lower clas- tation of about 90o. Staurolite porphyroblasts are tic sequence, which he named the Pine Hall For- euhedral, black, untwinned and may be up to 2 mation by an intervening gray shale which he cm in length. Oriented mica laths, ranging in elevated in rank from Cow Branch member to Cow length from 0.5 to 1 mm, eompose the matrix and Branch Formation. The central part of the basin produce a schistose texture. Micas, which form the is narrow and does not eontain the gray shale unit foliation, wrap around the garnet and staurolite (Cow Branch Formation). As a result the lower unit porphyroblasts. Chlorite, derived from alteration cannot be distinguished from the upper unit and of biotite, and staurolite porphyroblasts are ob- the rocks in this part of the basin are mapped as served in slightly sheared rock near the Ridgeway a single stratigraphic unit, which Thayer (1970) fault zone. retained the name Dry Fork Formation of Myer- tons, 1963). Thayer (1970) found that the border conglomerates on the southeast side of the basin Anna IV: DANVILLE BASIN underlie and intertongue with the Pine Hall For- mation, and that those border eonglomerates on the The Danville basin (Plate and Figure 1) contains northwest side of the basin overlie and intertongue continent derived, clastic sedimentary rocks that with the Stoneville Formation. Therefore, he does are correlated with early Late Triassic age rocks not recognize lhe Cedar Forest Formation as a of the Lockatong Formation of the Newark Super- stratigraphic unit. 18 VIRGINIA DIVISION OF MINERAL RESOURCES

Thoyer, unpublished

Thoyer, in Price Thoyer, 11 monuscripl of the Spring Myerlons, 1963 Thoyer,1970 l98OA ond l98OB Heniko, 1977 Gorden Quodrongle Cedor Forest g Formotion I col.) con lomerole cong lomerote unconform i ll - Leoksville Formolion Sfonevi I le Formolion I Dry Dry Dry Formoti on Cosc c do (sondslone i (sondslong ond Stotion Mbr. ,l Dry onO mudrock).jl I mudrock) (red shole For k 'ond Er sondsl Cow Fork For k rl Fo Cow Bronch rmo I ion Bronch Bronch (orkose: ond Formolion :l Formolion (sillslone, Formoiion I cloyslone, ond Formotion Formotion- shole) _;Formof ion | Le oksvi I le ol Formolion ond shole) $;(sondsfooe, (sondslone tone mudrock, Cow Bronch ; ond ond I Mbr. (groy Pine Holl Pine Holl al ond minor mudrock) mudrock) Pine Hcll il Formotion shole ond Formolion (sondslone (sondslone ond mudrock) ond mudrock)

cong I om erote cong I omerofe conglomerote

S oulhwesl Norl h e osf Figure 11. Stratigraphic relationships of rocks along strike from southwest to northeast in the Danville Triassic basin.

Both the Pine Hall and Stoneville formations clinorium. To the southwest in North Carolina this become finer grained from the margins toward the sequence is on strike with rocks of the Charlotte center ofthe basin. The units generally change from igneous belt and these rocks probably are the coarse fluvial and alluvial fan deposits at edges of eountry rocks that the igneous plutons intruded to the basin to medium- to light-gray shales locally produce this igneous belt. To the northeast, beyond interbedded with coarser clastic rocks in the center the study area in eentral and northern Virginia, of the basin (Thayer, 19?0). Fossil evidenee shows these volcanic and sedimentary roeks are on strike that these shales are at least partly lacustrine in with and are tentatively correlated with roeks of origin. a volcanic island-arc suite named the central Vir- ginia volcanic-plutonie belt (Pavlides, 1981). There Anna v: SourH CnNrnRl Vtnclxu, is a discrepancy between the age of the rocks in Metavoleanic-Plutonie Belt the southern Virginia Piedmont and the preferred M etaaolcanic and M etasedimentary Rocks age for the roeks that make up the belt to the northeast. Pavlides (1981) eonsiders the belt in A sequence of felsic and mafie metavolcanic rocks central and northern Virginia to be of probable that contains interlayered metasedimentary rocks Cambrian age, whereas Glover and others (1971) lies along the North Carolina boundary (Figure 2 report an age of 620 m. y. to 740 m. y. for rocks and Plate) from west of Danville eastward to along the North Carolina boundary just west of the beyond South Boston (Henika, 1977; Tobisch and Virgilina synclinorium (Figure 2). These dates Glover, l97l:. Kreisa, 1980). These rocks are were from zircons that might contain lead inherited bounded on the northwest by rocks of the Danville from older rocks. Triassic basin and on the southeast by roeks of the The base of the section of metavoleanic and Carolina slate belt contained in the Virgilina syn- metasedimentary rocks is not exposed within this PUBLICATION 59 19

study area. Tobisch and Glover (1971), Glover and ika, 1975, 1977; Tobish and Glover, 1971; Kreisa, others (1971) and Kreisa (1980) have mapped the 1980). In the area along the northwestern boundary, eontact between these rocks and the overlying the rocks are algreenschist facies and welded tuffs, Carolina slate belt (Figure 2) and have interpreted erystal tuffs, and volcanic breecias are still rec- this contact to be conformable. The abrupt change ognizable (Henika, L977). Where the metavolcanie in metamorphic grade from greenschist in the and metasedimentary rocks have reached silliman- Carolina slate belt to upper amphibolite in the ite grade, the lower unit consists of a sequence of metavolcanic-metasedimentary rocks to the west interlayered quartzo-feldspathic gneisses and horn- was thought to be a tightly compressed metamor- blende-plagioclase gneisses that probably also rep- phic gradient. Similarly, Secor and others (1983) resent highly metamorphosed volcanic and vol- find the eontact between the Charlotte belt and canic-sedimentary rocks. Interlayered schistose Carolina slate belt to be a metamorphic gradient, rocks observed in this unit could represent pelitic and further proposed thatthe slate belt is an exotic, interbeds. At sillimanite grade the upper unit is tenain that was first deformed in early Paleozoic a leucoeratic, poorly layered, quartzo-feldspathic time. In eontrast, beeause the rocks of the central gneiss (Henika, 1977; Price and others 1980A). Virginia voleanic belt are lithologically different Other high-rank rocks found in the lower unit of from the stratigraphie units in the Carolina slate this sequence are kyanite-mica sehist and silliman- belt and beeause rocks of the Carolina slate belt ite quartzite (Henika, 1977). physically overlie roeks of the eentral Virginia Graphite schist bands occur in the area underlain volcanie belt along the western boundary of the by rocks of the central Virginia metavolcanic belt Virgilina synclinorium, Conley (L974) concluded to the east as far as the vicinity of South Boston that the rocks of the Carolina slate belt are younger (Kreisa, 1980 and personal communication). Be- than rocks of the central Virginia volcanic belt. cause of the structural and stratigraphic similarity Pavlides (1976, 1981) shows that the stratigraphy of the graphite schist to the Arvonia Formation, and the geoehemistry of the central Virginia vol- which is on strike to the northeast, Conley (1978) canic belt and the Carolina slate belt are entirely suggested that the schist might be infolds of Ar- different and concludes that these two sequences vonia Formation into the metavolcanic-metasedi- ofroeks were parts ofseparatevoleanic and tectonie mentary rocks, rather than being graphitie inter- provinces. Perhaps in Cambrian time, rocks of the layers in these rocks. eentral Virginia volcanic belt formed as an island are sequence bordering North Ameriea and the Sheltan Farmation Carolina slate belt formed as a similar island are sequence on the Afriean Continent. Therefore, the The Shelton Formation is a felsic igneous.rock contaet between those two belts would indeed, originally named the Shelton Granite by Jonas represent a suture zone as suggested by Glover (1928) and renamed Shelton Formation by Henika (L974). (L977) because he found that at its type loeality In the area represented in the Plate, the meta- Jonas had included metamorphosed voleanie and volcanic and metasedimentary rocks are divided sedimentary rocks of the eentral Virginia voleanie into a lower unit and an upper unit (Henika,1977; belt in the granite. Although areas mapped as Price and others, 1980A and 19808). The lower unit Shelton Formation might contain very minor met- of the metavolcanic-metasedimentary rocks is in- asedimentary rocks, the Shelton as mapped by homogenous and composed of irregularly inter- Henika (L977) is a pink to gray, coarse-grained, layered felsic and mafic metatuff beds at the base two-mica sheared plutonic igneous roekthat ranges that grade upward into a more regularly layered in composition from quartz monzonite to granite. sequence of closely spaced layers of felsic and mafic The rock has been tectonically deformed and shows metatuffs containing minor metagraywacke layers a faint gneissosity. This gneissosity is cut by a non- (Henika, t977). The contact between the lower and penetrative foliation that produces a well.deve- upper units is drawn atthe top of a prominentmafic loped pencil rodding. The formation eontains mic- layer, whieh is the highest mafic layer in the rocline and perthite augen that are enclosed by sequence. The upper unit is eomposed of felsic biotite in a quartz-plagioclase matrix. Intrusive voleanic rocks and volcanie-sedimentary rocks. contacts seem to be conformable with the enclosing The core of this belt of metavoleanie and met- metavoleanie-metasedimentary rocks, indieating asedimentary rocks is at sillimanite grade (Figure either that the Shelton occurs primarily in eoncor- 3), and grade drops to greensehist facies along both dant plutons or there has been extreme flattening its northwestern and southeastern boundaries (Hen- and transposition of the contacts. 20 VIRGINIA DIVISION OF MINERAL RESOURCES

Henika (1977) originally thought that the lower micropegmatite; biotite forms vermieular inter- unit of the metavolcanie-metasedimentary se- growths in plagioclase along pyroxene boundaries. quence unconformably overlay the Shelton Forma- The diabases are thought to have originated in tion, and he eonsidered the Shelton to be a Grenville the upper mantle and ascended so rapidly into the basement roek. Stephen Kish (personal eommuni- overlying continental crust that there was insuf- cation, June, 1980) obtained a radiometric age ficient time for differentiation to take place (Rag- using Rb/Sr whole-rock method of.429+ 7 m.y. from land and others, 1971). The intrusion ofthese rocks the Shelton. This Rb/Sr age date indicates that the was probably related to development of tensional Shelton is not basement but rather is more likely fractures formed in response to release of stress an intrusive pluton in the Preeambrian-Cambrian just prior to the rending of the continent of Laurasia metavoleanie and metasedimentary rocks. The and formation of the Atlantic Ocean by sea floor Shelton slightly predates typical plutonic rocks of spreadingon opposite limbs of the North American- the Charlotte igneous belt, whieh range in age from Caribbean rift in the middle and late Jurassie 415 to 395 m. y. old (Fullagar,l97t; Fullagar and (Dietz and Holden, 1970). Butler 1975). The diabase dikes are probably of Jurassic age as indicated by a 40Ar/3eAr age date of 190 m.y. DhsA.sn Dlrns on the Palisades sill in New Jersey (Dallmeyer, 1975), by paleomagnetic data (De Boer, 1967), and Swarms of north and northwesterly trending, en by the occurrence of lava flows (probably fed by echelon diabase dikes oecur in the eastern. central diabases) interlayered with early Jurassic sedimen- and western parts of the area (Plate). There seems tary rocks in northern Virginia (Lindholm, 1979; to be two trends of diabases, one oriented about Cornet, L977). Ragland and others (1983) propose N20"W-N30.W and the other almost north-south. that the emplaeement of the north-south trending The northerly-trending dikes are wider than the dikes, postdates the emplaeement of the northwest- northwest-trending dikes and generally pinch and trending dikes. swell (Plate). Ragland and others (1983) show that the north-south set of dikes were emplaced in a STRUCTURE north-south set of fractures that converge near FoLDs Charleston, South Carolina. These north-south Blue Ridge Anti,cl;inmium dikes are more differentiated than the northwest- trending dikes (Ragland and others, 1968; Weigand Fold patterns in the Blue Ridge anticlinorium and Ragland, 1970; Ragland and others, 1971). are delineated by the amphibolites in the Lyneh- The dikes are medium-gray to black and range burg Group. F, isoclinal folds are warped by Fz from basalt at chilled margins to medium-grained isoclines to produce hook-shaped fold patterns typ- gabbro in the centers of larger intrusive bodies. ieal of type-3 fold patterns (Ramsey, 1967). The They are moderately resistant to chemieal weath- folds are now almost coplanar, but are not colinear. ering, which begins along joint surfaces and pro- Hinges of F, folds are subhorizontal, whereas F1 ceeds inwardly into the rock. This produces sphe- folds plunge at angles on the order of 45 degrees roidally weathered boulders and ocherous both to the southeast and northwest. The Ft folds saprolite. initially trended more northwesterly and were The diabases are composed of about 50 percent refolded by the northeasterly trending F, folds. The calcic plagioelase (Anbd and about 30 percent F, and F, folds were warped by large, gently augite. Magnetite is the major accessory mineral. plunging, open, northeast-trending, Fe struetures Onlythree of the diabases examined in thin sections such as the Cooper Creek anticline. A late-de- contain olivine (from 2 to 5 pereent). Textures are veloped, sub-horizontal crenulation cleavage oeeurs generally ophitic. Alteration is rather eommon at throughout the area. It is extremely well developed contacts between dikes and country roek; the al- along the Bowens Creek fault zone and might be teration is the product of hydration. As the dikes related to sub-horizontal thrust movement. are generally most altered at the contact with F, folds in the Candler Formation are steeply country roek, the water probably came from the plunging intrafolial isoclines. Fr folds in the for- enclosing country roek. Alteration minerals include mation are overturned to the northwest: the axial pale-green, fibrous serpentine, antigorite, talc and surfaees of these later folds dip to the southeast chlorite; also, plagioclase may be altered to sericitic at angles generally greater than 45 degrees. Ft mica. Some diabases show the results of hydroth- folds in the unit are broad, more open structures ermal replacement in the form of myrmekite and and trend northeastward. PUBLICATION 59 2l

Smith R'i,aer Allochthan Satnatoum M ounta'i,ns Anticlinari,um

The Smith River allochthon, is a northeastward- Roeks of the Sauratown Mountains anticlinorium trending polydeformed, rootless structure (Figure have been warped into creseent-shaped folds (Priee 2 and Plate). Mathematical modeling of gravity and and others 1980A, 19808) typical of the type-2 magnetic data indicates that the allochthon is a interference pattern (Ramsey, 1967). This pattern thin, sheet-like mass (Greenberg, 19?5). It is was produeed by the refolding of a southeastwardly bounded on the northwest by the southeastward- dipping isoclinal fold system (Fr) by a later (Fz) dipping Bowens Creek thrust fault and on the set of folds that had a trend almost normal to the southeast by the northwestward-dipping Ridgeway trend of the F, set of folds. Ft and F, folds are thrust fault. To the southwest along strike, the warped by upright north to northeast-trending Bowens Creek and Ridgeway faults converge and folds (F). The intersection of the F, and Fs folds merge at the Brevard zone (Rankin, Espenshade producei basin-and-dome, or type-l", interference and Newman,l97Z; Espenshade and others, 1975). patterns (Ramsey, 1967) as shown on the Plate. The The eastern margin of the Smith River allochthon development of the anticlinorium as a major re- is truncated by the vertical to steeply southeast- gional structure was followed by erosion causing ward dipping Chatham fault zone, which borders the removal of the rocks which once conneeted the the Danville Triassic basin. Smith River allochthon to the Inner Piedmont belt Folds within the Smith River allochthon now as a continuous thrust sheet. have a general N45oE trend. The earliest folds (F1) developed in the rocks of the allochthon are seen C entr al Vir gi,ni,a M etaaolcawi'c- Plutoni,e B elt at outcrop scale in the Fork Mountain Formation. These folds are so transposed in the plane of fo- The unnamed metavolcanic and metasedimen- liation that they probably do not greatly affeet tary rocks east of the Danville basin contain an general outcrop patterns of rock units. Many of early set of recumbent isoclines (Ft folds) that have these F, folds are hook-shaped and many are root- U-shaped hinges and plunge gently either to the less fold noses, as seen both in outcrop and thin northwest or to the southeast (Henika, 1980). No sections. A second set of folds (Fz) is at map scale foliation is developed parallel to the axial surfaees and warps the foliation. These F, folds have a of these folds, indicating that they formed prior northeasterly trend and an upright to steeply south- to the time of regional metamorphism. A second eastward-dipping non-penetrative cleavage which set of folds (Fr) are tight isoclines with V-shaped is developed parallel to their axial planes. They hinges that are overturned to recumbent. Pene- are refolded by a more northerly trending set of trative foliation cuts the hinges of these folds in- upright folds (F3). The F, system, which is probably dicating that they are synmetamorphic. Tobish and equivalent in age to the F, system in the Sauratown Glover (1971) interpreted these two fold systems Mountains area, formed during or after emplace- as representing ongoing development; they envi- ment of the allochthon because it warped both the sioned folding to have begun prior to the onset of roeks of the allochthon and rocks that underlie the metamorphism and to have been completed before allochthon. the end of metamorphism. A later set of open, The allochthon is now preserved in a northeast- upright folds (F) trend northeastward and plunge erly trending, shallow basin that probably formed both to the northeast and to the southwest. These during the F, folding event as an interference folds are colinear but are not coplanar with F, folds. pattern produced by the refolding of F, folds. A nonpenetrative shear foliation developed parallel The Phase II fold system of Stirewalt and Dunn to F* axial surfaces euts the penetrative S, foliation (1973), whieh, they proposed, produeed the "James developed during F, folding. River synclinorium," probably developed at this Henika (1977) states that early folds have the same time. Development of the Sauratown Moun- characteristic mushroom or crescent shape of atype tains anticlinorium and the Blue Ridge anticli- 2 interference pattern (Ramsey, 1967). This pattern norium is also probably equivalent in age to this was produced when gently inclined isoclinal Ft F, event. The development of these antielinoria as axial surfaces were refolded by Fz isoelines, which major regional structures probably was either coe- are more steeply inclined. Hook-shaped folds (type val with, or later than, emplacement of the Smith 3 interference pattern; Ramsey, 1967) resulted River allochthon because the Smith River alloch- from the superimposition of Fr folds on F2 folds thon is preserved in a synformal structure between (Henika, 1977). This fold pattern is also displayed these two anticlinoria. just east of the study area (Tobish and Glover, 1977). 22 VIRGINIA DIVISION OF MINERAL RESOURCES

The only foliation in the Shelton Formation is (Figure 2). It truncates the Ridgeway fault in the the nonpenetrative shear cleavage developed dur- south-central part of the area and from there ing the Fs fold event (Heni ka, lg7 7 ), ind icating that northeastward forms the northwestern boundary the Shelton is post tectonic and intruded preex- of the Smith River allochthon. At the North Ca- isting structures that eontained earlier developed rolina boundary, the fault has an approximate F, and F, folds. The F, folds are probably Taconic trend of N45oE, and it can be traced in this in age as they are older than the Shelton, which direction to an area east of Sandy Level (Plate and is a Silurian age intrusive. The F, folds are prob- Figure 2), where it assumes an almost east-west ably of Aeadian age, because thby postdate the direction. Farther northeastward the fault strikes Shelton. approximately N50oE, which is its trend direetion through the rest of the area to the north. The fault Interregional Fold,s dips 60o to 70o south or southeast. The Chatham fault eonsists of a zone of cataclasis Rocks throughout the study area contain northw- that has been displaced by later, north-trending estward-trending, broad, open warps that are ev- and northwest-trending vertical normal faults identlythe youngestfolds in the Virginia Piedmont. (Plate). Geologic mapping (Henika, 1977; Price and These folds were first recognized by Conley and others 1980A, 19808) indicates that highly sheared Toewe (1968) in rocks of the Smith River allochthon. rocks occur in zones as mueh as 0.5 mile wide along They have since been recognized by Henika (1977) the Chatham fault and that these zones include in the area east of the Danville basin, by McCollum cataclastic rocks derived both from the igneous and (Roeky Mount and Gladehill quadrangles) in the metamorphic rocks that lie northwest of the Dan- Blue Ridge antielinorium, and in the central Vir- ville basin and the sheared Triassie age sedimen- ginia Piedmont (Poland, Glover and Mose, 1g?g). tary rocks within the basin. Highly sheared Henika noted Ihat a local northwest-trending gneisses, granites and pegmatites are locally rec- spaced cleavage is associated with these folds and ognizable. postulated that the folds were formed by post- The fault zone records more than one period of Triassic block movement along north- to northwest- movement and a change from ductile to brittle trending shear planes. It is possible that the fold deformation. It is thought that movement probably system developed at the time of formation of major oecurred over an extended period of time. Robinson faults such as the Stony Ridge (Butler and Dunn, (1979) reported undeformed pegmatite intruding 1968) and Chatham faults (Figure 2) as a result mylonite along this fault zone. This pegmatite has of north-south compressional forces which could not been dated, but mica from one of the pegmatites generate left-lateral movement along these faults. in the Ridgeway mica district was dated by the A tensional complement to this stress regime would Rb-Sr method at32l m.y. (Mississippian) (Deuser be in a northwest direction, whieh also is a major and Herzog, L962). This dated pegmatite probably trend direetion of the diabase dikes in the region. formed during what is thought to be the last major This is further supported by the fact that the period of metamorphism in the region. Mylonites northerly-trending set of diabase dikes are wider intruded by this unsheared pegmatite show recrys- than the northwest-trending set of dikes. These tallization and eontain prograde garnet whose for- dikes also pinch and swell, whereas the northwest- mation postdates the last eataclasis (Robinson, trending set generally have a fairly constant width. 1979). A younger microbreecia (breccia composed This indieates that the northerly-trending set was of fragments of pre-existing mylonite and mylonite subject to dilation during emplacement, and that breccia) and massive cataclasite, whieh do not show they were emplaced in fractures normal to the recrystallization, are also present (Robinson, 1979; direction of maximum tension. This was an east- Price and others, 19804 and 19808). The eatac- west direction and therefore perpendicular to a lastic roeks have been exposed to hydrothermal north-south direction of maximum compression solutions because they are cut by quartz veins and suggesting that the fractures might have been are locally silicified. Some fractures are filled with produced by a rightlateral shear couple. chlorite containing pyrite inclusions. Riebeckite of apparent hydrothermal origin occurs in fractures Flur,rs in the cataclacite (W. S. Henika, personal commu- Normal Faults nication, 1978) and in fractures in the Triassic rocks Chatham Fault within the Danville basin (Allen, 1967). Samples of silicified microbreccia along the southwestern The Chatham fault (Myertons, 1963) bounds the extension of the Chatham fault in North Carolina northwestern part of the Danville Triassic basin have been dated as Early Jurassie age, 180+ 3 m.y. PUBLICATION 59 23

ago (Fullagar and Butler, 1980). The Chatham fault is absent (Thayeli,n Henika, 1977).If movement locally shows brittle deformation which indieates on the fault had oecurred after deposition, dips a later period of movement than the ductile de- should be more shallow in the areas where the fault formation that produced the mylonites. is present than where it is absent. Loeal areas of relatively high potassium-uranium concentrations are shown along the fault zone by aeroradioactivity maps (Virginia Division of Min- Unnomed, Faults qnd Shear Zones eral Resources, 1979) and prospectingfor uranium was begun in 1978 in the environs of the Danville A major fault occurs in the north-central part basin by Marline Uranium Corporation, a subsid- of the area (Plate and Figure 2). The fault trends iary of Marline Oil Corporation (Marline Oil Cor- about N20oE; two splays have more easterly trends. poration, 1982). Drilling bJ'Marline was begun in The structure is a hinge fault that to the north 1979, and the program identified a high grade movement is up to the east and to the south move- uranium deposit located 6 miles northeast of Cha- ment is up to the west. The fault has displaeed rocks tham. An average ore content is reported to be 4 of both the Smith River allochthon and the Blue lbs. per ton and reserves are estimated to be in Ridge anticlinorium. Where gneisses (Bassett For- the order of 30 million pounds of uranium oxide mation) oecur on either side of the fault zone, they (Us0e). The host for the deposit is sheared rocks have been altered to silieified mylonite and cata- of the Fork Mountain Formation and other rocks clasite, but where the fault is bounded by schists of the Smith River allochthon (Marline Oil Cor- (Fork Mountain Formation and the metasedimen- poration, 1982). tary rocks of the Lynchburg and Candler forma- The sedimentary roeks within the Danville basin tions), the rocks are sheared into button schists, strike N44oE +11o and dip N44'W +9o (Thayer, but no mylonites are developed. This fault displaces 'inHenika,1977). The consistency of the trend and the Bowens Creek thrust fault and the thrust fault dip of these rocks indicates that little movement along the southeastern Candler-Lynehburg con- occurred along the Chatham fault during deposi- tact; therefore, it is younger than these major tion of the sediments that fill the basin. If movement thrusts of the region. had occurred. during deposition it would be ex- A shear zone that has a trend of N80oE has been pected that the older sedimentary rocks within the traced from the eastern boundary of the map (Plate) basin would have a greater angle of dip than the southwestward through Ringgold to about the cen- younger roeks of the basin. The last movement ter of the city of Danville, a distanee of about 7 along the Chatham fault probably postdates depo- miles (Henika, 1977). This shear zone contains sition. This last movement along the fault rotated mierobreccia and lenses of eataclastie rock. The the rocks within the basin from the horizontal to new minerals calcite epidote and stilbite have a northwest dip and thus produced a northwest grown in the sheared roeks of this shear zone. A dipping monoclinal sedimentary wedge within the body of microbreccia in this shear zone is located basin. along the Norfolk and Southern Railway 0.7 mile Vandola Fault northeast of Ringgold. This microbreccia is cut by a Mesozoie diabase dike indicating that the devel- The Vandola fault (Price and others 19808) is opment of the shear zone preceded the intrusion a border fault on the east side of the Danville basin of this dike. in the south-eentral part of the area (Plate). It has A seeond shear zone that has a trend of about been traced for about 9 miles in a northeasterly N15'E is located about 2.3 miles due east of New direction from the North Carolina boundary. Far- Mountain Cross (Plate). This fault can be traced ther to the northeast along strike, this fault is absent in a northeasterly direetion for approximately 2.8 and Triassic sedimentary rocks restunconformably miles to the sorrthwestern edge of the Danville on underlying metamorphic roeks. The fault dips Triassic basin where it intersects the Vandola fault to the northwest at angles ranging from 50" to 60o. (Henika, L977). Cataclasite oecurs along the extreme northeastern A third shear zone can be traced for about two part of the fault trace for about 1.5 miles (Thayer miles in a N60oE direction from the southern 'in Henika, 1977).It is inferred that movement on boundary of the map (North Carolina state bound- the Vandola fault preceded deposition of sediments ary) in the area 0.8 mile NW of Rutledge Creek in the basin because (as previously noted) rocks in southwest of Danville. This zone contains sheared the basin have a constant northwest dip both in and locally lenses of extremely sheared (cataclastic) the areas where it is present and areas where it rock (Henika,1977). 24 VIRGINIA DIVISION OF MINERAL RESOURCES

Thrust Faults (Plate and Figure 2). The fault has a sigmoidal Bowens Creek Fault trace (Plate) and dips to the northwest, under the allochthon. An exception is in the area where it The Bowens Creek fault (Conley and Henika, converges with the Brevard zone southwest of the 1970) bounds the northwestern edge of the Smith present study area (Espenshade and others, 1975). River allochthon and has a sinuous trace that trends There, the fault has been overturned and dips to generally N50oE (Figure 2). In the present study the southeast. Reentrants along the trace of the area the Bowens Creek fault is very close to the fault suggest that the fault plane is folded. The location of the Martie thrust fault as shown by Jonas lack of development of appreciable shearing along on the 1928 edition of the Virginia State Geologie the fault zone suggests that it, like the northeastern Map. As noted previously, mathematical modeling segment of the Bowens Creek fault, either could of gravity and magnetic data indicates that the have developed at relatively shallow depth or was Smith River allochthon is a shallow structure a subhorizontal fault aeeompanied by high fluid (Greenberg, 1975). The dip of the fault plane of pressure. the Bowens Creek fault is to the southeast and is less steep than that of the penetrative foliation Termination of the Smith Riuer Allochthon developed in rocks bounding the structure. The to the Southwest fault plane dips most steeply in the southwestern part of the area and is almost flat to the northeast To the southwest both the Bowens Creek and as indieated by the fault trace, which eneircles a Ridgeway faults verge and finally merge with the small window along Walker Creek in the north- system of faults that make up the Brevard zone central part of the study area; a reentrant at in North Carolina. The Brevard zone is composed Dickenson, whieh is just east of the window; and of a number of faults, eaeh of which from its point a larger reentrant in the northeastern part of the of emergence can be traced northward in a direc- area (Plate). Across the southwestern and central tion that is more northerly than the trace of the part of the area, a shear zone is developed along Brevard zone proper. This is because the top thrust this fault. However, to the northeast, little or no sheet in the stack, namely the Inner Piedmont shearing aeeompanies the fault, except for loealized thrust sheet, has a more easterly trend than the areas where a sub-horizontal, spaced cleavage is underlying sheets. This trend probably resulted developed primarily in the footwall. The absence from the development of later folds such as the Blue of major shear zones developed by thrust faults is Ridse anticlinorium, the synform that preserves interpreted by Elliott and Johnson (1980) to mean the Smith River allochthon and the Sauratown formation at shallow depths. If this interpretation Mountains anticlinorium. Geologic mapping of the is correct, it would indicate that the fault developed extreme southeastern edge of the Grandfather at shallow depths in the northeast and at greater Mountain window (Conley and Drummond, 1981) depth to the southwest. An alternative explanation shows that even the Blue Ridge thrust sheet verges might be that to the north the allochthon moved with and finally merges with the Brevard zone. on a sub-horizontal fault plane and was thrust Bryantand Reed (1970)and Conleyand Drummond forward with little effort, probably aided by high (1981) have shown that the plane of the fault at fluid pressure within the fault plane. To the south the base of the Blue Ridge thrust sheet along the the steeper dip angle of the fault plane would northwestern edge of the Grandfather Mountain suggest that, in this area, the thrust sheet was window dips gently to the northwest, but to the riding up a ramp surface, which afforded greater southeast it is rotated and dips steeply to the resistance to movement; with aceompanying pos- southeast just before entering the Brevard zone. sible loss of fluid pressure, this may have resulted This is similar to what happens to the Ridgeway in a greater amount of friction and produced the fault which, as previously noted, to the northeast resulting shearing. dips to the west at a shallow angle, but to the southwest is rotated so that it dips to the southeast Ridgewag Fault before entering the Brevard zone (Espenshade and others, 1975). This rotation is caused by the fact The Ridgeway fault (Conley and Henika, 1973) that both the Grandfather Mountain window and is a thrust that bounds the southeastern part of the Sauratown Mountains anticlinorium are win- the Smith River allochthon and separates it from dows of para-autochthonous rocks (Bryant and the Sauratown Mountains anticlinorium, whieh Reed, 1961; Conley, 1978). Both antiformal struc- bounds the allochthon to the south and southwest tures are gentle, open warps to the north, but their PUBLICATION 59 25

northwestern limb becomes progressively stee- central and northern Virginia (Conley, 1978) is pened and finally overturned to the southwest apparently stratigraphically overlain (by the Ca- before each enters the Brevard zone. The devel- toctin) a relationship that would suggest that the opment of all these structures is probably controlled Lynchburg was obducted onto the continental crust by development of a ramp in the subsurface and and subjeeted to erosion prior to the outpouring bending of westward moving subhorizontal thrust of the Catoctin metabasalts in late Precambrian plates as they are forced to ride over this ramp or earliest Cambrian time. surface. Thrust faults bouniling the C and,ler Formation Probable Tlmtst Faults At The Base of Ophioli,tes In The ltUnchburg Graup In the area of study, the Candler Formation crops out in the form of a northeast-oriented, V-shaped As noted previously, the ultramafic and mafic splay that dies out to the southwest. To the west metaigneous and metavoleanie rocks occur at sev- the Candler Formation is in fault contact with the eral intervals in the stratigraphy of the Lynehburg underlyingAlligator Back Formation of the Lyneh- Group in both the Blue Ridge and Sauratown burg Group, and to the east the Alligator Baek Mountains anticlinoria. These repeated sequenees Formation is thrust back over the Candler. The of metamorphosed ultramafic, gabbroic and basal- fault, which has thrust the Alligator Back Forma- tic rocks overlain by metasedimentary rocks sug- tion over Candler, completely overrides and cuts gest that the formation is composed of stacked piles out the Candler to the southwest. The fault dis- of ophiolites and their cover roeks repeated by appears under the northwestern boundary of the thrust faulting. Two intervals of roeks of ultra- Smith River allochthon. The two fault planes whieh mafic, gabbroic and basaltic composition were enclose the wedge of Candler dip southeastward recognized in the rocks of the Lynchburg Group at angles of about 50 degrees. in the Sauratown Mountains anticlinorium; one is Berquist (1980) suggests that both of the faults at the base of the Ashe Formation and one at the that bound the wedge of Candler are thrust faults. base of the Alligator Back Formation. These two Berquist (1980) explained the structure as a re- intervals may represent a single ophiolite and cumbent syncline of Candler, thrust over the Lynch- cover-rock sequence. In this scenario the coarser- burg. Certainly such an explanation would account grained quartzo-feldspathic rocks (probably prox- for the juxtaposition of younger rocks over older imal turbidites) of the Ashe Formation with ophi- roeks. An alternative explanation is that the strue- olites composed of ultramafic rocks, metagabbros ture is a sequence of exposed decollement zones, and metabasalts at their base were overthrust by wherein roeks of Candler and Lynchburg are more pelitic rocks (probably distal turbidites) of stacked one above the other through the develop- the Alligator Back Formation, also with ophiolites ment of ramps. Recent Vibroseis data from the at their base. This stacked sequence was then central Virginia Piedmont (Harris and others, obdueted onto Grenville age continental crust 1982) indicate that the structure of the Piedmont (Stuart Creek Gneiss). is a major decollement off which ramp thrusts have The interpretation that these rocks are repeated been generated, thus teleseoping the rocks into sequences of ophiolites and their cover rocks would repetitive sequences. These sequences are generally suggest that each sequence is separated by a fault separated by sub-horizontal thrust planes. There- at the base of each ophiolite. During geologic fore, late developing ramp faults can thrust mapping, faults have not been recognized at the younger rocks that were deeper in the repetitive base of every mafic-ultramafic sequence. Shear thrusted pile over older roeks that had been pre- zones have been mapped at the top of the Stuart viously ramped and are higher in the staek (but Creek Gneiss (Grenville basement) in the Saura- not higher in the stratigraphic section). This leads town Mountains anticlinorium (Conley and Henika, to the conclusion that the Candler is indeed bounded 1973). Shear zones have also been recognized in by thrust faults, to produce a duplex similar to that rocks of the Blue Ridge anticlinorium both at the proposed by Boyer and Elliott (1982) for other parts base of and within the metagabbro body west of of the southern Blue Ridge and Piedmont. The Fairystone Lake (Conley and Henika, 1970), at the presence of a ramp structure would explain both top of the Ashe Formation in the Cooper Creek the straight-line trace of the fault and the rather anticline, and at the base of the gabbro-ultramafic steep dips (45"-50") recorded along the fault trace. body underlying Grassy Knob north of Rocky That normal, rather than thrust movement, might Mount. The eroded surfaee of the Lynchburg in also have occurred on these ramp surfaces during 26 VIRGINIA DIVISION OF MINERAL RESOURCES

the time when the faults were active cannot be through the present study area. Major differences ignored, especially toward the end of this period, in these two interpretations are as follows: wheh relaxation of compressive forces might have occurred, producing listric normal faults. 1. The Catoctin Formation is a unit of subaerial metabasalts and arkosic metasedimentary rocks REGIONAL SIGNIFICANCE OF THE (Reed and Morgan, 1971) that lies stratigraphi- PRESENT STUDY cally between the Lynchburg Group and the SrcNrrrclNCE OF Opnrolrrns? IN THE Candler Formation. Mapping by the writer on LyNcHeunG GRoup the southeast limb of the Blue Ridge anticlinorium shows that the Catoctin thins and finally The presence of possible ophiolites in the rocks pinches out northeast of Lynchburg, and the of the Lynehburg Group shows that the Lynchburg rocks previously considered to be Catoctin green- meta-sedimentary rocks, some of which are inter- stone interlayered with the top of the Lynchburg layered with basalts at the top of the candidate Group by Brown (1958) are actually metabasalts ophiolite sequenees, were likely deposited on ocea- contained within the Alligator Back Formation nic crust, now represented by the ophiolites. The of the Lynchburg Group. The top parts of these Lynchburg metasedimentary rocks and underlying metabasalt sequences are interlayered with oceanic crust (ophiolites) would have been obducted Lynchburg metasedimentary rocks that are onto the North American continental crust (now deep marine metasedimentary rocks, in part of represented by Grenville-age rocks in the cores of turbidite origin; therefore these basalts are not the Blue Ridge and Sauratown Mountains anti- of subaerial flows. clinoria) during a late Precambrian closing event. 2. The eontact between the Candler and the un- This was prior to the vast outpouring of Catoctin derlyingAlligator Back Formation of the Lynch- continental metabasalts directly onto the Lynch- burg Group is not a stratigraphic contact but burg on the southeast limb of the Blue Ridge a fault contact Berquist (1980). In the Buffalo anticlinorium, an event which heralded the begin- Ridge 7.5 minute quadrangle, which is northeast ning of continental break up and formation of the of the Lynchburg 15-minute quadrangle, the Iapetus Ocean in latest Precambrian-earliest writer has found a fault (probably the same fault Cambrian time. The absence of the Lynchburg on mapped by Berquist farther to the southwest) the northwestern limb of the Blue Ridge anticlin- that has cut out the Catoctin Formation, and orium is the result of erosion prior to deposition the Catoctin is not exposed to the southwest of the Catoetin. The Catoctin flows poured out on beyond this point. an erosional surface (Reed, 1955) that had deve- 3. The Evington Group has been regarded as a loped on the Lynchburg to the east and on Grenville continuous stratigraphic sequenee of rocks that basement to the west, where the Lynchburg had occupies the core of the James River syncli- been eroded away. norium (Brown, 1958; Espenshade, 1954). It contains the Candler Formation at the base of A RUNTonPRETATIoN OF the section and the Slippery Creek greenstone Tur: Jauns RwnR SyNcr,rxonruvr at the top. Work in the present study area shows that the geolory is more complex than a simple Work by Redden (1963) in the Altavista 15- stratigraphic sequence contained in an open minute quadrangle, which borders the northeast- synformal fold. The contact between the Candler ern part of the present study area, provides a Formation and structurally overlying forma- connecting link with rocks mapped by Espenshade tions has also been mapped in detail by Berquist (1954) and Brown (1958) in what they called the (1980) in the Sandy Level quadrangle and by James River synclinorium. A number of persons Conley and others in the Penhook quadrangle have mapped the rocks of the James River syn- (in preparation), and the contact in these quad- clinorium and considerable controversy has de- rangles is also a fault eontact. To the southwest veloped concerning stratigraphic relationships this fault cuts out the Candler and places the within the structure (Table). rocks that structurally overlie the Candler in Figure 12 is a sequence of block diagrams that contact with rocks of the Alligator Back For- compare previous interpretations by Brown (1958) mation, a formation older than the Candler. The of the geology of the Lynchburg quadrangle with overlying rocks are metagraywackes and graph- the present interpretation of a larger area from ite sehists that are identical to the typical Al- the Lynchburg quadrangle southwestward ligator Back Formation. Therefore, rocks that PUBLICATION 59 27

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-|d 9.r F 9,tr v8 € E€ g E€ .€n 5'* S Bc! :ttr xE <9oFa .Eb tr! F ix ;-i 5tr: _o 9r- ott :l tV -'t j

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r-'l a H s tr a X Ee 9a d I z ..5 €€ .E€ E E E gg cB o EE +E €E rE Es tr r-'1 g* b0 F* 5* 5* 5" 5" +) t{ +ta dno.rg uofuyrg @ rO +) 5 tr si ,. ,\e s ", (J z 65 €Fg E* E € E q) F A6 ;HH Fs gH €F €B 5il Ee €r Es. E-,r Eefr i€

dnorg uol6uurg 28 VIRGINIA DIVISION OF MINERAL RESOURCES

Stippery Creek greenstonel E o t3 I Mount Athos formolion, l6 J Pelier schist, l: E { arcn morble, ond lF lJoshuo schist, l,i I =ffi I undilferenfioied E Condler formotion E Cofoclin greenstone ffi E Lynchburg gneiss

ORIGINAL INTERPRETATION ROCKS OF BLUE RIDGE ANTICLINORIUM IE Condler Formotion m Cofoctin Formotion? E Lynchburg Formolion- gneisses, schists, morbles, ond quortzites E Ophiolites ol bose of Lynchburg Formofion- ullromufic rocks, melogobros, ond metobosolts @ Grenville-oge bosemenl rocks in the core of lhe Blue Ridge onliclinorium Kft ROCKS OF SMITH €'//*t, i-_ _ RIVER ALLOCHTHON F @ Fork Mounloin Formalion E Amphibolife ot lop of Eosseff Formotion E Bossefl Formolion- gneiss fuo- E Rocks underlying decollememenl surfoce probobly in porl composed of lower Poleozoic rocks now exposed in lhe lY "- 'g=€* Volley ond Ridge lo rm lhe wesl --: -s

REINTERPRETATION

Figure 12. Block diagrams showing the original interpretation and reinterpretation of the stratigraphy and structure of the James River synclinorium.

physically overlie the Candler are not younger overlies the Catoctin, but rather a single for- units belonging to the Evington Group but be- mation, the Candler Formation, whieh overlies long instead to the Alligator Back Formation, the Catoctin. which has been thrust over the Candler. Thus 4. Bland (1978), by chemical analyses, found that it appears that there is no Evington Group that the Slippery Creek greenstone, a greenstone at PUBLICATION 59 29

the top ofthe sequence of rocks previously called They are actually the biotite gneiss and amphib- the Evington Group, exhibits many charaeter- olite of the Bassett Formation. the lowest stra- istics of continental rift basalts, and further- tigraphic unit in the allochthon, that, as pre- more, he found that it is chemically indistin- viously noted, might be of Grenville age. guishable from the metabasalts of the Catoctin 8. In summation, the rocks that were thought by Formation. Therefore, the Slippery Creek green- Brown (1958) to occupy the southeastern limb stone would actually be the Catoetin Formation of the James River synclinorium actually are in normal stratigraphic order, overlying the rocks of the Smith River allochthon, which have Lynchburg Group, but contained in a more been thrust tens of miles northwestward to their eastward thrust plate. present position. They eannot physically connect 5. Present mapping shows that the thrust fault with rocks that should eompose the west limb previously mapped just southeast of the axis of of the James River synclinorium. Thus the in- the James River synclinorium in the Lynchburg ference by Brown that the James River syncli- quadrangle (Brown, 1954) is a continuation of norium is a simple open fold containingyounger the Bowens Creek fault, which separates rocks rocks in its core and older rocks on its limb is of the Blue Ridge anticlinorium to the northwest not eorrect. These roeks are not continuously from rocks of the Smith River allochthon to the connected aeross a simple synclinal structure, southeast. and the rocks on what should be the northwest- 6. The schistwhich lies alongthe southeastern edge ern limb of the structure have an entirely dif- of the Bowens Creek fault is described by Brown ferent geologic history from those on the south- (1958) as a garnet-mica and staurolite-garnet- western limb of the proposed synclinorium. mica schist that shows partial to complete retrograde metamorphism of staurolite to chlorite and sericite and garnets to ehlorite. Beeause this REFERENCES schist shows polymetamorphism similar to that seen in the Fork Mountain Formation and be- Achaibar, J. and Misra, K. C., 1984, Amphibolites cause two stages of metamorphism an not known of the Smith River allochthon, southwest Vir- to occur in the Candler, it is inferred that this ginia, Southern Appalachians (abs.): Geol. Soe. rock belongs to the Fork Mountain Formation. America Abstraets with Programs, vol. 16, no. Similar schists of the Fork Mountain occur along 3, p. 121. the northwestern edge of the Smith River al- Allen, G. C., 1967, Riebeckite oceurrenee in south- lochthon to the southwest. Schists of the Fork ern Virginia: Virginia Minerals, vol. 13, no. 1, Mountain universally show polyphase metamor- p. 10. phism and the most obvious effect has been that Allison, D. T., Ragland, P. C., Conley, J. F. and amphibolite grade minerals have been retro- Odom, A. L., 1984, The Martinsville igneous graded to greenschists. Typically the Fork Moun- complex of the Smith River allochthon: An tain schists along the northwestern boundary of Andean plutonic suite (abs.): Geol. Soc. Amer- the Smith River allochthon contain staurolite ica Abstraets with Programs, vol. 16, no. 3, p. that has been retrograded to chlorite and seri- r22. cite. The Candler Formation has been examined Berquist, C. R., 1980, Sandy Level quadrangle, by the writer from its type locality at Candlers Virginia: its geology and regional interpreta- Mountain east of Lynchburg, southwestward to tion,in Price, V, Jr., Thayer, P. A. and Ranson, where it terminates in the present study area. W. A., eds., Geologieal investigations of Pied- Throughout this area the Candler shows met- mont and Triassic rocks, central North Caro- amorphism that does not exceed greenschist lina and Virginia: Carolina Geological Society facies. It never shows prograde metamorphism Field Trip Guidebook, p. C.G.S. 80 B I 1 - C. to amphibolite grade and retrograde metamor- G.S.80BI10. phism back to greensehist facies. in preparation, Geology of the Sandy 7. Rocks in the core of the Sherwill anticline have Level and Callands quadrangles: Virginia Di- previously been correlated with the Lynchburg vision of Mineral Resources. Group in the core of the structure overlain by Bland, A. 8., 1978, Trace element geochemistry Catoctin Formation on the limbs of the structure - of volcanic sequences of Maryland, Virginia, (Brown, 1958). As these rocks are within the and North Carolina and its bearing on the Smith River allochthon, they are not directly teetonie evolution of the central Appalaehians: correlative with the Lynchburg and Catoctin. Ph. D. Dissertation, University of Kentucky. 30 VIRGINIA DIVISION OF MINERAL RESOURCES

Boyer, S. E. and Elliott, D., 1982, Thrust Systems: Virginia Division of Mineral Resources Rept. Amer. Assoc. Petroleum Geologists Bull., vol. Inv.22, 46 p. 66,no. 9, p. 1196-1230. 1973, Geology of the Snow Creek, Mar- Brown, W. R., 1951, Major structural features in tinsville East, Price, and Spray quadrangles, the Lynchburg quadrangle, Virginia (abs.): Virginia: Virginia Division of Mineral Resour- Virginia Journal of Science, vol. 2,(new series), ces Rept. Inv.33,71 p. no.4, p.346-347. -Conley, J. F. and Drummond, K.M., 1981, Geologic Brown, W. R., 1953, Structural framework and map and mineral resources summary of the mineral resources of the Virginia Piedmont: northeast 1/4 Marion quadrangle, North Caro- Kentucky Geol. Survey, Ser.9, Special Pub. no. lina: North Carolina Department of Natural 1, p. 88 - 111; Virginia Division Geol. Reprint Resources and Community Development, Di- No. 16. vision of Land Resources, Geologic Survey Sec- Brown, W. R. 1958, Geology and mineral resources tion, Geologic Map 210-NE, 6 p. of the Lynchburg quadrangle, Virginia: Vir- Conley, J. F., Piepul, R. G., Lemon, E.M., Jr. and ginia Division of Mineral Resources Bull. 74, Robinson G. R., Jr., in preparation, Geologie 99 p. map of the Penhook and Mountain Valley quad- Bryant, Bruce, and Reed, J. C., Jr., 1961, The Stokes rangles: Virginia Division of Mineral Resour- and Surry counties quartzite area, North Ca- ces. rolina-a window?: U. S. Geol. Survey Prof. Cornet, Bruce, 1977, Palynostratigraphy and age Paper 424-D, p. D61-D63 of the Newark Supergroup: Unpublished Ph.D. 1970, Geologaof the Grandfather Moun- Dissertation, Pennsylvania State University. tain window and vicinity, North Carolina and Dallmeyer, R. D., 1975, The Palisades sill: A Ju- Tennessee: U. S. Geol. Survey Prof. Paper 615, rassic intrusion? Evidence from a0Ar/3eAr in- 190 p. cremental release ages: Geology, vol. 3, no. 5, -Butler, J. R. and Dunn, D. 8., 1968, Geology of p.243-245. the Sauratown Mountains anticlinorium and De Boer, J. L967, Paleomagnetic-tectonic study of vicinity, in. Guidebook for field excursions: Mesozoic dike swarms in the Appalachians: Geol. Soc. America, Southeastern Geology Jour. Geophys. Research, vol. 7 2, no. 8, p. 2237 - Spec. Pub. l,p.19-47. 2250. Coleman, R. G., 1977, Ophiolites - ancient ocean Deuser, W. G. and Herzog, L.F., 1962, Rubidium- lithosphere?: New York, Springer Verlag Pub- strontium age determinations of muscovites lishers, 229 p. and biotites from pegmatites of the Blue Ridge Conley, J. F., 1978, Geology of the Piedmont of and Piedmont: Jour. Geophys. Research, vol. Virginia - Interpretations and problems, in 67, no. 5, p. 1997-2004. Contributions to Virginia geology - III: Vir- DieIz, R. S. and Holden, J. C., 1970, Reconstruetion ginia Division of Mineral Resources Publica- of Pangaea: breakup and dispersion of conti- tion 7, p. 115-149. nents, Permian to present: Jour. Geophysical 1981, Stratigraphic relationships be- Researeh, vol. 75, no. 26, p. 4939-4956. tween rocks of the Blue Ridge anticlinorium Elliott, D. and Johnson, M. R. W., 1980, Structural and the Smith River allochthon in the south- evolution in the northern part of the Moine western Virginia Piedmont, in Conley, J. F., thrust belt, NW Scotland: Transactions of the - Marr, J. D., Jr. and Berquist, C. R., Jr., Stra- Royal Soeiety of Edinburg; Earth Sciences, vol. tigraphic Relationships between rocks of the 71, p.69-96. Blue Ridge anticlinorium and Smith River Espenshade, G. H., 1954, Geology and mineral allochthon in the southwestern Virginia Pied- deposits of the James River.Roanoke River mont: 13th Annual Virginia Geologic Field manganese district, Virginia: U. S. Geol. Sur- Conference, Virginia Division of Mineral Re- vey Bull. 1008, 155 p. sources, p. 1-28. Espenshade, G. H. and others, 1975, Geologie map Conley, J. F. and Toewe, E. C., 1968, Geology of of the east half of the Winston-Salem quadran- the Martinsville West quadrangle, Virginia: gle, North Carolina-Virginia: U. S. Geol. Sur- Virginia Division of Mineral Resources Rept. vey Misc. Inv. Series Map I-709-B. Inv. 16, 44 p. Fenneman, N. M., 1938, Physiography of Eastern Conley, J. F. and Henika, W. S., 1970, Geology of United States: New York. McGraw-Hill Book the Philpott Reservoir quadrangle, Virginia: Co., 714 p. PUBLICATION 59 31

Fullagar, P. D., 1971, Age and origin of plutonie Virginia, with sections on the Triassic System intrusions in the Piedmont of the Southeastern by Thayer, P. A.: Virginia Division of Mineral Appalachians: Geol. Soc. America Bull., vol.82, Resources Publication 2, 45 p. p.2845-2862. Henika, W. S. and Thayer, P. A., 1980, Geologic Fullagar, P. D. and Butler, J. R., 1975, Age and map of the Spring Garden quadrangle, Vir- chemistry of leucocratic adamellites in the ginia: Virginia Division of Mineral Resources Charlotte Belt of North Carolina (Abs.): Geol. Publication 48, Geologic Map 47D. Soc. America Abstracts with Programs, vol. 7, Hunt, C. B., 1972, Geolory of soils, their evolution no.4, p.491. and classification: H. Freeman and Co.. San 1980, Radiometric dating in Sauratown Franciseo,334 p. Mountains area, North Carolina, ,in Priee, Y., Harris, L. D., De Witt, W. Jr., and Bayer, K. C., Jr., Thayer, P. A. and Ranson, W. A., eds., 1982, Seismic-reflection data in the Central Geological investigations of Piedmont and Tri- Appalachians (abs.): Geol. Soc. America Ab- - assic rocks. eentral North Carolina and Vir- stracts with Programs, Northeastern-South- ginia: Carolina Geological Society Field Trip eastern combined Meeting, vol. 14, nos.2 and Guidebook, p. C. G. S. 80 B 11 1-C. G. S. 80 3,p.23. 8116. Jonas, A.. L., 1927, Geologic reconnaissance in the Fullagar, P. D. and Dietrich, R. V., 1976, Rb-Sr Piedmontof Virginia: Geol. Soc. Ameriea Bull. isotopic study of the Lynchburg and probably vol. 38, no.4, p.837-846. correlative formations of the Blue Ridge and 1928, Geologic map of Virginia: Vir- western Piedmont of Virginia and North Ca- ginia Geol. Survey. rolina: American Jour. Sci., vol. 276, no. 3, p. 1932, Geology of the Kyanite belt of 347-365. Virginia, 'i.nKyanite in Virginia: Virginia Geol. Furcron, A. S., 1969, Late Precambrian and early - Survey Bull. 38, p. 1-38. Paleozoic erosion depositional sequences of King, P. 8., 1955, A geologic section across the northern and central Virginia: Georgia Geol. - southern Appalachians- an outline of the geol- Survey Bull. 80, p..57-88. ogy in the segment in Tennessee, North Caro- Glover, L., III, 1978, Speculation on the relation lina, and South Carolina, in Russell, R. J., ed., between eastern and western Piedmont vulea- Guides to Southeastern Geologa: Geol. Soc. nism (Abs.): Geol. Soc. America Abstracts with America., vol. 66, no. 1, p. 332-373. Programs, vol. 6, no.7, p.757. Kreisa, R. D., 1980, Geology of the Omega, South Glover, L., III and others, L97t, U-Pb dating of Boston, Cluster Springs, and Virgilina quad- Carolina Slate Belt and Charlotte belt rocks, rangles, Virginia: Virginia Division of Mineral Virgilina District, Virginia and North Carolina Resourees Publication 5,22 p. (Abs.): Geol. Soc. America Abstracts with Pro- Lemmon, R. E., 1981, An igneous origin for the grams, vol. 3, no. 5, p.313. Henderson augen gneiss, western North Caro- Glover, L., III and Sinha, A. K., 1973, The Virgilina lina: evidence from zircon morphology: South- deformation, a late Precambrian or Early Cam- eastern Geology, vol.22, no.2, p.79-90. brian orogenic event in the eentral Piedmont Lindholm, R. C. 1979, Geologic history and stra- of Virginia and North Carolina: American tigraphy of the Triassic-Jurassic Culpeper ba- Jour. Sci., vol.273-A, p.234-251. sin, Virginia: Summary: Geol. Soc. Ameriea Greenberg, Jeffrey K., 1975, Tectonic implications Bull., Part I, vol. 90, no. 11, p. 995-997. of geophysical evidence in the Martinsville, McCollum, M. S., in preparation, Geologic maps Virginia area (abs.): Geol. Soc. America Ab- of the Rocky Mount and Gladehill quadrangles: stracts with Programs, vol. 7, no. 4, p. 493-494. Virginia Division of Mineral Resources. Henika, W. S., 1971, Geology of the Bassett quad- Marline Oil Corporation, 1982, Marline Oil Cor- rangle, Virginia: Virginia Division of Mineral poration Annual Report, 1982: Marline Oil Resources Rept. Inv. 26, 43 p. Corporation,4l p. 1975, Progressive regional metamor- Marr, J. D., Jr., 1984, Geologic mapof the Pittsville phie gradient in rocks southeast of the Danville and Chatham quadrangles, Virginia: Virginia Triassic basin, Virginia (abs.): Geol. Soc. Amer- Division of Mineral Resources Publication 49, ica Abstracts with Programs, vol. 7, no. 4, p. Geologie Map 47B,47C. - 449. Mason, Roger, 1978, Petrology of metamorphic 1977, Geology of the Blairs, Mount rocks: George Allen and Unwin Ltd. publishers, Hermon, Danville and Ringgold quadrangles, London,254p. 32 VIRGINIA DIVISION OF MINERAL RESOURCES

Middleton, G. V. and Hampton, M. A., 19?3, Sed- ginia: Virginia Polytechnic Institute and State iment gravity flows: mechanics of flow and University, p. 1l-14. deposi,tion, im Turbidites and deep-water sed- Price, Van and others, 1980A, Geology of the Whit- imentation: SEPM Pacific Seetion Short mell and Brosville quadrangles, Virginia: Vir- Course, Anaheim, p. 1-38. ginia Division of Mineral Resources Publica- Mose, D. G. and Conley, J. F., 1983, Evidence for tion 2l-, Geologic Map 16A, 16 D. Acadian high-grade metamorphic rocks in the Price, Van and others, 19808, Geology of the Axton Blue Ridge of southwestern Virginia (abs.): and Northeast Eden quadrangles, Virginia: Geol. Soc. America Abstracts with Programs, Virginia Division of Mineral Resources Pub- vol. 15, no.2, p.95. lication 22, Geologic Map 168, 16C. Myertons, C. T., 1963, Triassic formations of the Ragland, P. C., L974, Geochemieal evidence for the Danville basin: Virginia Division of Mineral existence of two igneous rock series, Martins- Resources Rept. Inv. 6, 65 p. ville igneous complex (abs.): Geol. Soe. America Odom, A. L. and Russell, G. S., 1975, The time of Abstraets with Programs, vol. 6, no. 4, p. 390. regional metamorphism of the Inner Piedmont Ragland, P.C., Rogers, J. J. W., and Justus, P. S., and Smith River allochthon: inferences from 1968, Origin and differentiation of Triassic whole rock ages (abs.): Geol. Soc. America dolerite magmas. North Carolina, U. S. A.: Abstracts with Programs, vol. 7, no. 4, p. 522- Contributions to Mineralogy, vol. 20, p. 57-80. 523. Ragland, P.C., Brunfelt, A. O. and Weigand, P. W., Olsen, P. 8., Remington, C. L., Cornet, B., and 1971, Rare-earth abundances in Mesozoic dol- Thomson, K. S., 1978, Cyclic changes in Late erite d ikes from eastern Un ited States :'in Brun- Triassic lacustrine communities: Science, vol. felt, A. O. and Steinnes, E., eds., Activation 201, no. 4357 , p.729-733. analysis in geochemistry and cosmochemistry: Pavlides, Louis, 1976, Piedmont geology of the Oslor Universitetsforlaget. Oslo-Bergen Fredricksburg, Virginia area and vicinity: Tromso, p.227-235. Geol. Soc. America, Northeastern-Southeast- Ragland, P.C., Hatcher, R. D., Jr. and Whittington, ern Section Meeting Arlington, Virginia., 1976, D., 1983, Juxtaposed Mesozoic diabase dike sets Guidebook for Field Trips 1 and 4,44 p. from the Carolinas: a preliminary assessment: 1981 The central Virginia volcanic- Geology, vol. 11, no. 7, p.394-399. plutonic belt: an island are of Cambrian (?) age: Ragland, P.C., Conley, J. F. and Odom, A. L., in U. S. Geol. Survey Prof. Paper 1231-4, 34 p. preparation, Teetonic setting and erystalliza- 1980, Revised nomenclature and stra- tion history of the Martinsville igneous com- - tigraphic relationships of the Fredricksburg plex, southwestern Virginia Piedmont. Complex and Quantico Formation of the Vir- Ramsey, J. G., 1967, Folding and fraeturing of ginia Piedmont: U. S. Geol. Survey Prof. Paper rocks: McGraw-Hill Book Company Publishers, - 1146,29 p. New York, N. Y.,568 p. Pearce, J. A. 1976, Statistieal analyses of major Rankin, D. W., 1970, Stratigrphy and structure of element patterns in basalts: Jour. Petrology, Precambrian rocks in northwestern North Ca- vol. 17, p. 15-43. rolina, an. Fisher, G. W., and others, eds., Stud- Pearce, J. A. and Cann, J. R., 1971, Ophiolite origin ies of Appalachian geology-central and south- investigated by discriminant analysis using Ti, ern: New York, Interscience Publishers, p. 227 - Zr, and Y: Earth and Planetary Sci. Letters, 245. vol. 12, p. 339-349. 1975, The continental margin of eastern 1973, Tectonic setting of basic volcanic North America in the Southern Appalachians: rocks determined using trace element analyses: the opening and elosing of the Proto-Atlantic Earth and Planetary Sci. Letters, vol. 19, p. Ocean: American. Jour. Sci., vol.275A, p.298- 290-300. - 336. -Pegau, A. A., 1932, Pegmatite deposits of Virginia: Rankin, D. W. and others, 197L, From the Blue Virginia Geol. Survey Bull. 33, 123 p. Ridse anticlinorium to the Sauratown Moun- Poland, F. B., Glover, L.,III and Mose, D. G., 1979, tains anticlinorium - a major synclinorium and The geology of the rocks along the James River the Brevard fault zone (abs.): Geol. Soc. Amer- between Sabot and Cedar Point, Virginia: iz ica Abstracts with Programs, vol. 3, no. 7, p. Glover, Lynn, III and Read, J. F., eds., Guides 677-678. to field trips 1-3 for Southeastern Section Meet- Rankin, D. W., Espenshade, G. H. and Neuman, ing, Geol. Society of America, Blacksburg, Vir- R. B., 1972, Geologic map of the west half of PUBLICATION 59 33

the Winston-Salem quadrangle, North Caro- Palmer, A. R., 1983, Confirmation of the Ca- lina, Virginia, and Tennessee: U. S. Geol. Sur- rolina slate belt as an exotie terrane: Seienee, vey Misc., Inv. Series Map I-709-A. vol. 221, no. 4611, p. 649-651. Rankin, D. W., Espenshade, G. H. and Shaw, K. Smith, J. W., Milici, R. C., and Greenberg, S. S., W., 1973, Stratigraphy and structure of the 1964, Geology and mineral resources of Flu- metamorphic belt in northwestern Virginia - vanna County: Virginia Division of Mineral A study from the Blue Ridge across the Brevard Resources Bull. 79,62 p. zone to the Sauratown Mountains anticlino- Stirewalt, G. L. and Dunn, D. E., 1973, Mesoscopic rium: American Jour. Sci., vol. 273-A, p. 1-40. fabric and structural history of Brevard zone Redden, J. A., 1963, Stratigraphy and metamor- and adjacent rocks, North Carolina: Geol. Soc. phism of the Altavista area, in Weinberg, E. America Bull., vol.84, no. 5, p. 1629-1650. L., and others, Geological excursions in south- Thayer, Paul A., 1970, Stratigraphy and geology western Virginia: Virginia Polyteeh Institute of Dan River Triassic basin, North Carolina: Engineering Extension Service, Geol. Guide- Southeastern Geology, vol. 12, no. 1, p. 1-32. book 2, p. 77-86. Tobisch, O. T. and Glover, Lynn, III, 1971, Nappe Reed, John C., Jr., 1955, The Catoctin Formation formation in part of the Southeastern Appa- near Luray, Virginia: Geol. Soc. America Bull., lachian Piedmont: Geol. Soc. America Bull., vol. vol.66, no. 7, p.871-896. 82, no. 8,p.2209-2230. Reed, John C., Jr. and Morgan, Benjamin A., 1971, Virginia Division of Mineral Resources, 1979, Aero- Chemical alteration and spilitization of the radiometric contour map of the Danville Tri- Catoctin greenstones, Shenandoah National assic basin: Virginia Division of Mineral Re- Park, Virginia: Journal of Geology, vol. 79, no. sources Open File map, scale l:24,000. 5, p. 526-548. Walker, R. G., 1978, Deep-water sandstone facies Robinson, G. R., Jr., 1979, Pegmatite cutting mylo- and ancient submarine fans: models for explo- nite-evidence supporting pre-Triassic faulting ration for stratigraphie traps: Ameriean Assoc. along western border of the Danville Triassic Petroleum Geologists, vol. 62, no. 6, p. 932-966. basin, southern Virginia (abs): Geol. Soc. of Weigand, P. W. and Ragland, P. C., 1970, Geochem- America Abstracts with Programs, vol. 1,1, no. istry of Mesozoic dolerite dikes from eastern 4,p.210. North America: Contributions to Mineralogy Secor, D. T., Jr., Samson, S.L., Snoke, A. W. and and Petrolog:y, vol. 29, p.195-2L4.