carolina geological society

Carolina Geological Society

Officers 1966-67

President: William J. FurbishDuke UniversityDurham, North Carolina

Vice President: Maurice MageeTennessee Copper CompanyDucktown, Tennessee

Secretary-Treasurer: S. Duncan HeronDuke UniversityDurham, North Carolina

Field Trip Leader: Douglas W. RankinU.S. Geological SurveyWashington, D.C.

CAROLINA GEOLOGICAL SOCIETYGuidebook for 1967 Annual Meeting

Pages 1-20

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INTRODUCTION

The field trip this year will focus on the Blue Ridge fothe first time since 1960. In contrast to many of our recetrips, hardrock exposures are plentiful, and much of the geogy in the vicinity of the Mt. Rogers area is well know. Thtwo are perhaps not unrelated! The Martha Washington Iin Abingdon, Virginia, will be our headquarters. The trip wispan an altitude range of 3,700-feet – from 1,800-feetmore than 5,500-feet. In mid-October the higher altitudcan be very cold. Bring warm clothes; gloves may not amiss. Transportation on Saturday will be by bus excsively. Please cooperate with this as the trip is over narrmountain roads and includes a toll road. Saturday mornthere will be a level walk of about a mile; and in the aftenoon a hike of about 1-miles near the summit of WhitetMountain will include an easy climb of 500-feet. The Suday trip will be by automobile, will involve a little walkingand will end near West Jefferson, Ashe County, North Calina.

The Mt. Rogers area includes the junction of VirginiNorth Carolina and Tennessee and is in the western hathe Winston-Salem 1° x 2° quadrangle (Figure 1). The acovered by the field trips extends from the unmetamophosed Paleozoic rocks of the Valley and Ridge belt on northeast, across the Unaka belt, and into the Precambcrystalline rocks of the Blue Ridge belt (terminology froKing, 1955, p. 338). Rocks of this area include a thick maof upper Precambrian stratified rocks, the Mount RogeVolcanic Group, at the northwest edge of the crystalline bThe Mount Rogers Volcanic Group is atypical of most uppPrecambrian rocks in the Appalachians in that it contaabundant rhyolites. In fact, it contains one of the two largmasses of felsic volcanic rocks in the eastern United StaThe other is of Devonian age and is in Maine. The MouRogers is of further interest because it contains evidencelate Precambrian glaciation. The contact between the MoRogers Volcanic Group and the overlying basal Lower Cabrian (?) clastic rocks is well exposed; one of the best exsures will be visited. Several large thrust faults pass throuthe area. Although no stops are planned to see the thruswe will make stops in several tectonic units, and weathpermitting, the topographic expression of several thrusheets will be visible.

All field trips stops will be in the Unaka and Blue Ridgbelts. The Saturday trip will emphasize the structural astratigraphic setting of the Mount Rogers Volcanic Group well as the internal stratigraphy of the group. The Sund

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trip will emphasize the older Precambrian granitic basemon which the Mount Rogers rests and the effects of Paleometamorphism. If time permits, we will visit exposures othe Roan and Carolina Gneisses, of former usage (Ke1903) now thought to be higher-grade rocks roughly corretive with the Mount Rogers (Rankin, 1967 a).

My work in the Mt. Rogers area began in 1962 with tmapping of the Whitetop Mountain 7¾-minute quadrangfor the U.S. Geological Survey. In 1965, the detailed maping was suspended in favor of small-scale reconnaissamapping of the Winston-Salem (1° x 2°) quadrangle. I1965, I considered this assignment a dubious honor, but hsince become a very enthusiastic 1° x 2° mapper, at leasthe Blue Ridge.

A number of earlier studies in and around the Mt. Roers area have been published and are noted below budetailed stratigraphy of the Mount Rogers Volcanic Grouhas never been determined. These earlier studies are inpensable in reconnaissance mapping. Much of the area cered by the field trip is included in the report on the geoloof northeastern most Tennessee by King and Fergu(1960). Although I disagree with some aspects of this repoit has been a major influence on my thinking. A.J. Stose aG.W. Stose did considerable mapping, both detailed areconnaissance in the Mt. Rogers area, and some of twork has been published recently (Stose and Stose, 19Miller (1944) mapped the Paleozoic rocks north of the MRogers area as part of a World War II manganese study.

On Sunday the field trip will be in the area mappemany years ago by Keith (1903). Finally, this study has beinfluenced by and is, in fact, an outgrowth of the work oBryant and Reed in the Grandfather Mountain area to south (Bryant and Reed, 1962).

REGIONAL GEOLOGY

The following general discussion of Appalachian geoogy represents and accumulation of information from masources. It is certainly influenced by the various syntheseP.B. King.

A major axis of older Precambrian crystalline rockextends as a chain of anticlinoria along the Appalachmountain system from the Long Range in Newfoundlanthrough the Green and Berkshire Mountains in NeEngland, the New Jersey Highlands, and the Reading Prin Pennsylvania to the Blue Ridge in the Southern Appachians. The older Precambrian rocks are not known with c

GUIDE TO THE GEOLOGY OF THE MT. ROGERS AREA, VIRGINIA , NORTH CAROLINA AND TENNESSEE

Douglas W. RankinU.S. Geological Survey

Washington, DCRetyped and reformatted November 1999

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tainty to extend farther southwest than southwestern NoCarolina. The anticlinoria with older Precambrian rocks their cores do extend for a distance of 1,800-miles and clearly a major feature of Appalachian geology. The axisclose to the western margin of the belt of Paleozoic memorphism and also corresponds in a general way to change from miogeosynclinal rocks on the west to eugeoclinal rocks on the east in the Paleozoic Appalachian geoscline.

In many places along the axis between the older Pcambrian rocks in the cores and the overlying Paleozoic simentary rocks are stratified rocks of various metamorphgrade generally assigned a late Precambrian age. Thesesist mainly of clastic sedimentary rocks. The upper Precabrian rocks rest with profound unconformity upon the oldPrecambrian, although in some areas this unconformity only recently been recognized because of the effects of Pozoic metamorphism. In many areas the upper contacobscured by faulting, but in the central and southern Appachians, where these rocks are in stratigraphic contact wthe overlying basal Lower Cambrian and Lower Cambri(?) clastic rocks (the Chilhowee Group) there is commonno recognizable difference in metamorphic grade or degof deformation. In Maryland, Virginia, and northwesterNorth Carolina, the upper Precambrian rocks probably thto a featheredge not far northwest of the older Precambanticlinorium and apparently thicken to the southea(Brown, 1958; Hopson, 1964; and Rankin, this study).

South of New York, the age of the basement granigneisses is now reasonably well established as 1,100 1,000 million years (Tilton and others, 1960 and Davis aothers, 1962). If we take 550 m.y. as the approximate datethe base of the Cambrian (Glaessner, 1963), that leavtime interval roughly equivalent to the duration of Phanezoic (Cambrian to Recent) time for the deposition of uppPrecambrian sediments in the Appalachians. It is probaunwarranted, albeit convenient, to consider them all coeva

In the Blue Ridge belt of northwestern North CarolinKeith (1903) recognized that granitic rocks predominaalong the northwest edge of the crystalline belt and that throcks are structurally overlain on the southeast by schimica gneisses, and amphibolites. There has been much troversy over the origin and mutual relations of these crysline rocks and whether any or all of them are of laPrecambrian age. Mapping of the Winston-Salem 1° x quadrangle has demonstrated that a nonconformity separolder granitic rocks to the northwest from the overlying strified gneisses, schists, and amphibolites to the southeThese stratified metamorphic rocks that Keith (1903) callthe Carolina and Roan Gneisses are thought to be of latecambrian age and in part, at least, correlative with the MoRogers Volcanic Group that rests nonconformably upon tgranitic gneiss to the northwest. The geology in northweern North Carolina is thus similar to that of the Blue Ridge

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northern Virginia: an anticlinorium with a relatively narrowcore of older granitic rocks is flanked on both sides by upPrecambrian stratified rocks (Figure 2).

Most obvious structural features in the Mt. Rogers adate from either Paleozoic deformation and accompanymetamorphism, or Paleozoic thrust faulting and accompaing folding. The thermal peak of the metamorphism occurbefore the major thrusting because metamorphic isogradsoffset by the thrusting.

At least one episode of Paleozoic regional metamphism, probably roughly the same age as the 350-m.y.-pegmatites at Spruce Pine, North Carolina, has left imprint on the Mt. Rogers area. There is a metamorphic gdient across the area from unmetamorphosed Paleorocks of the Valley and Ridge belt to rocks of the kyanite astaurolite zones near West Jefferson, North Carolina. Mrocks of the Mount Rogers Volcanic Group have been memorphosed to low grade. Mafic rocks of the Mount RogeVolcanic Group have been metamorphosed to low graMafic rocks in the Mount Rogers are greenschists (albepidote-chlorite-tremolite assemblages), and many of tmetagraywackes contain stilpnomelane. The metamorpgradient may be traced across the older granitic gneiss incore of the anticlinorium by mineralogic changes in madikes cutting the gneisses. Toward the northwest, these dare greenschists. Toward the southeast, the dikes are gaamphibolites.

Cataclastic deformation accompanied the mineralogichanges and also increased in intensity toward the southThe effects of shearing are most obvious, however, in low-grade rocks in the core of the anticlinorium. Furthsoutheast, where the degree of recrystallization is greaterrocks are deformed in a more homogeneous manner rathan along discrete macroscopic planes.

South of Roanoke, Virginia, the Valley and Ridge belt characterized by an imbricate structure. Thrust faults afound at least as far east as the edge of the crystalline bethe Blue Ridge. In northwestern North Carolina, the larGrandfather Mountain window exposing lower grade Cabrian and Precambrian rocks beneath higher grade rockthe Blue Ridge demonstrates that virtually the entire BlRidge is allochthonous here (Bryant and Reed, 1962). Malines of evidence both in the Blue Ridge and Valley anRidge belts, such as mineral streaking, overturning of folfacies of Paleozoic sedimentary rocks, and the offsetmetamorphic isograds, indicate that the direction of thrustwas northwest.

In the Mt. Rogers area, most pelitic rocks have a wedeveloped foliation dating from middle Paleozoic metamophism. In general, this foliation dips southeast, but it is comonly deformed by northeast-trending crinkles that probadate from the major episode of thrusting. In places, a secomore steeply dipping foliation developed parallel to the axplanes of the crinkles. Over much of the area, a pervas

GEOLOGY OF THE MT. ROGERS AREA

Figure 1. Tectonic units.

3

DOUGLAS W. RANKIN

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southeast-plunging lineation, caused by mineral streakigrooving and long axes of pebbles and spherulites, also dfrom the period of thrusting. Because this lineation is in tsame direction as the tectonic transport, it is an a-lineation

A series of mountain ridges help up by basal Cambrand Cambrian (?) clastic rocks of the Chilhowee Group lbetween the crystalline allochthonous rocks of the BlRidge and the unmetamorphosed miogeosynclinal rocksthe Appalachian Valley (eastern carbonate part of the Valand Ridge belt). This area, called the Unaka belt by Ki(1955), consists of one or more thrust sheets now though

4

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be tectonically between the Blue Ridge thrust sheet and imbricately faulted Valley and Ridge belt. The thrust sheeof the Unaka belt are further distinctive in that they involvboth crystalline basement rocks and Paleozoic stratifrocks. Figure 1 shows tectonic units and accompany thrfaults that we will be discussing during the field trip. Thlarge Mountain City window is in northeastern Tennessbetween the Shady Valley thrust sheet and the Blue Rithrust sheet. King and Ferguson (1960, p.79, 83) concluthat rocks of the Shady Valley thrust sheet were originadeposited southeast of the Mountain City window. Region

Figure 2. Geologic map of the Mt. Rogers area showing the location of field trip stops. Geology in Tennessee modified from King andFerguson, 1960. Geology in Virginia and North Carolina by D.W. Rankin


5

DOUGLAS W. RANKIN

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considerations show that the minimum northwest transpof the Shady Valley thrust sheet is 18-miles in the vicinity longitude 82°W (the west edge of the Winston-Salem 1°2°).

King and Ferguson (1960) placed the Mount RogeVolcanic Group entirely within the Shady Valley thrust sheMuch of the group is now known to be above the StoMountain fault and in the Blue Ridge thrust sheet. Furthmore, the Catface fault is not continuous with the IroMountain fault around the northeast end of the MountaCity window, but overrides it (Rankin, 1967 b.) The Catfacfault is in turn overridden by the Stone Mountain fault farthto the northeast. The Mountain City window is thus an eyewindow as King and Ferguson concluded it was, but for dferent reasons.

ROCK UNITS

Core of the anticlinorium

Cranberry GneissThe oldest rocks mapped in the Mt. Rogers area are g

nitic gneisses that are continuous with the Cranberry Gneof Cranberry, North Carolina. Where least affected by Palezoic metamorphism along the northwest edge of the BRidge thrust sheet and in the Shady Valley thrust sheet, Cranberry is an igneous plutonic rock that occurs in bodof batholithic size. Compositions range from diorite to graite; most rocks are quartz monzonite. Biotite is probably primary dark mineral in quartz monzonite. Hornblende, wior without biotite, is the primary dark mineral in diorite anquartz diorite. Sphene is a common accessory in all rocTextures range from fine to medium grained and equigranlar to porphyritic. Phenocrysts of microcline are commonas much as one-inch long and rarely as large as 2¾ incWhere sheared, the equigranular rocks are flaser gneiand the porphyritic rocks are augen gneisses. The CranbGneiss is about 1,050 m.y. old (Davis and others, 1962)middle Precambrian in the informal usage of the U.S. Gelogical Survey.

Intrusive mafic rocksIrregular bodies of gabbro and dikes of diabase, all mo

or less metamorphosed, intrude rocks as young as the rhlite in the upper part of the Mount Rogers Volcanic GrouSimilar rocks west of the Grandfather Mountain windowere called Bakersville Gabbro by Keith (1903). They ahere thought to be intrusive equivalents of the late Precabrian mafic volcanism. Some may be as young as basathe Unicoi Formation of Early Cambrian (?) age.

The intrusive mafic rocks range in texture from vefine-grained diabase to coarse gabbro. Some, particularlyfiner grained ones, contain relict plagioclase phenocryswhich may be as large as 2¾ inches across and are textu

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similar to porphyritic lavas in the Mount Rogers.In places the dikes make up as much as 30 percent o

Cranberry terrane over areas as large as three square mWhere shearing is intense and mafic rocks abundant, crcutting contacts are uncommon, and a layering of grangneiss and greenstone or amphibolite results. These laygneisses have been interpreted by some as metasedimerocks (Eckelman and Kulp, 1956; Bryant, 1962).

Intrusive felsic rocksFelsic dikes and sills, though much less common th

mafic dikes and sills, are also found in the Cranberry Gneand in rocks as young as rhyolites in the middle part of Mount Rogers Volcanic Group. Some are porphyritic, cotaining a variety of phenocryst assemblages, mostly incling quartz and feldspar. Commonly quartz phenocrysts aembayed and alkali feldspar phenocrysts are highly perthhaving the patch perthite texture typical of alkali feldspphenocrysts in rhyolites of the Mount Rogers. The felsdikes and sills are thought to be related to late Precambvolcanism

Where shearing is strong, these felsites are sericite plites and, like their mafic counterparts, tend to be paracformable. Some recent workers interpret many of these roas phyllonite and mylonite (Hamilton in King and Ferguso1960, p.13).

Outside the Mt. Rogers area, larger felsic plutonic boies intrude the Cranberry Gneiss or correlatives. Theinclude the Beech Granite in Watauga and Avery CountiNorth Carolina (Bryant, 1962), the aegirine-augite graniteCrossnore, Avery County, North Carolina (Bryant 1962) athe Striped Rock Granite, Grayson County, Virgin(Riecken 1966). During the present study, I have foundsizeable body (8 square miles) of sodic pyroxene-beargranite in Watauga County, North Carolina. Although tabsolute ages of these granites are uncertain, the rocks mineralogic features shared by the rhyolites of the MouRogers Volcanic Group. Fluorite and zoned allanite araccessory minerals to all, and sodic amphibole occurs ingroundmass of some rhyolites in the Mount Rogers. Thgranites are, therefore, thought to belong to the same mmatic cycle as the late Precambrian volcanism.

Northwest flank of the anticlinorium

Mount Rogers Volcanic GroupThe Mount Rogers Volcanic Group is a sequence ab

10,000-feet thick of interbedded and interfingering volcanand sedimentary rocks all metamorphosed to low grade. volcanic rocks range in compositions from basalt to rhyolitintermediate compositions of flow rocks are uncommoThick masses of rhyolite constituting about 50 percent of tformation are the most distinctive feature of the formatiand hold up the three highest mountains in Virginia. Subdisions of the group proposed by Stose and Stose (1957) h


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not proved practicable.The group may be roughly divided into three parts. T

lower part consists of interbedded sedimentary rocks, baand rhyolite. Thick masses of rhyolite make up the midpart and sedimentary rock containing minor basalt and rhlite makes up the upper part. Calcareous sandstone andcareous shale are sparingly present in parts of the group,limestones are absent. Most of the sedimentary rocks wformed from poorly sorted, immature sediments.

Sedimentary rocks of the lower part of the group acharacterized by somewhat metamorphosed gray or greish-gray, muddy-matrix conglomerate, gritty graywacklaminated siltstone, shale, and minor calcareous sandstMost of the rocks are semischists, and the conglomerate ctains stretched pebbles and boulders. Bedding is poordefined in the conglomerate and graywacke.

Three rhyolite units have been mapped in the massrhyolite forming the middle part of the group. Each may brecognized by the phenocryst assemblage and each occurs in the same stratigraphic order within each of thtectonic units. The rhyolite units are called here from oldeto youngest C, B and A. Alkali feldspar phenocrysts, whepresent, are typically highly perthitic and have a patchy teture of the two phases within the crystal outline. Rhyolite the oldest and the thinnest, contains 5 to 20 percent pherysts of perthite and plagioclase in subequal amounts. Onbasis of scattered observations of flow banding, rhyolite Cprobably lava. Rhyolite B is either nonporphyritic or contains a few percent small phenocrysts of quartz and perthFlow banding, some chaotic, is visible in many outcrops, athe bulk of this unit consists of lava flows. Ash-flow tuffhave been recognized locally but are difficult to trace and probably minor. The groundmass of some samples of lavcompletely spherulitic, and in some, the spherulites stretched so that the long axes of the ellipsoids plunge soeast parallel to the regional “a” lineation. Rhyolite A, thyoungest, contains abundant, commonly 30 percent, phenrysts of quartz and perthite in subequal amounts. The bulkrhyolite “A” consists of welded ash-flow sheets suggestingsubaerial environment for this part of the Mount Roge(Rankin, 1960). The three rhyolites have an aggregate thness of 5,000-feet or more near Mt. Rogers, thought to beapproximate size of a volcanic center.

Arkose, rhythmite, and laminated pebbly mudstone atillite, all maroon, characterize the upper part of the grouNumerous examples of soft sediment deformation are pserved. The arkose may be crossbedded, and graded bedis exceptionally well developed in the rhythmites. Somrhythmites contain outsized clasts of both plutonic and vcanic rocks. Carrington (1961) suggested that the rhythmwere tuffaceous and that the larger fragments in them marelated to volcanic activity. The rhythmites certainly hadvolcanic source area in part but are probably of epiclastic gin. Clasts of patch perthite, probably derived from the rhy

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lite phenocrysts, have been identified in them. Many silt asand-size clasts of plutonic microcline are also preseShards, if present, have not been identified. Because mothe clasts are Cranberry Gneiss, they were probably rainto place. The age of the beds and the size of the clastmuch as about one-meter across) indicate that ice is the mreasonable mechanism for rafting. Interbedded with anabove the rhythmites are massive, poorly sorted, muddy, rmatrix, polymict conglomerate-tillite. The close associatioof pebbly varied rocks with the conglomerate suggests tboth rocks are of glacial origin. Harland and Rudwick (196have summarized evidence for a general late Precambglaciation.

The age of the Mount Rogers Volcanic Group is fairwell established as late Precambrian (Jonas and Stose, 1and Rankin, 1966). The group rests nonconformably on tCranberry Gneiss and was deposited upon a Precambtopography that had relief great enough so that at one por another nearly every unit within the formation form botom to top is in contact with the Cranberry. Boulder-sizclasts of Cranberry Gneiss are found locally in all major simentary and volcanic units of the Mount Rogers. The grois in stratigraphic contact with the overlying Unicoi Formtion of Early Cambrian (?) age for many miles. Stose aStose (1957) and King and Ferguson (1960, p.31) thouthat the contact was unconformable. I have followed the ctact for 30-miles along strike in the Shady Valley thrust shand find no evidence for an unconformity.

Chilhowee GroupThe Chilhowee Group in the Mt. Rogers area is divid

into the Unicoi, Hampton and Erwin Formations followinthe usage of King and Ferguson (1960). The group is sotimes refereed to as the “basal Lower Cambrian clarocks” (King, 1955, p.365) and the age of the group has bthe subject of much philosophical discussion. The youngformation of the group, the Erwin, passes upward throucarbonatic sandstone of the Helenmode Member into sparsely fossiliferous Lower Cambrian Shady DolomitOlenellus has been reported from the Helenmode Memb(see Neuman and Nelson, 1965) and Laurence (Laureand Palmer, 1963) has discovered Lower Cambrian fossilBlount County, Tennessee, in rocks correlative with the mdle of the Erwin Formation. Scolithus, generally thought tobe the fillings of worm tubes, occurs in beds as low as tHampton Formation, but it cannot be used for dating (Neman and Nelson, 1965). The US Geological Survey includthe Erwin Formation in the Lower Cambrian and LowCambrian (?). The Hampton and Unicoi Formations arethe Lower Cambrian (?).

King and Ferguson (1960, p.33) describe the ChilhowGroup as follows: “Rock types are relatively few and arinterbedded in frequent alteration. Basal conglomerate aarkose give place gradually to clay shale, siltstone and vi

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ous quartzite.” They give the thickness of the Chilhoweenortheastern most Tennessee as averaging 4,000-feetreaching a maximum of 7,500-feet on Iron Mountain. Imost of their measured sections away from Iron Mountahowever, the base of the Unicoi has been faulted out.

Unicoi Formation — The Unicoi Formation may be con-veniently divided into a lower heterogeneous division of conglomerate, sandstone, shale and basalt and an upper mhomogeneous division dominantly of sandstone. Rusty-weathering quartz-pebble conglomerate is commonly the lowest rock type in the Unicoi and contrasts markedly withthe underlying tillite and maroon rhythmite of the Mount Rogers.

Basalts, some amygdaloidal and porphyritic, occur the upper part of the lower division. Typically one or twobasalts are present in a given section, but three are founsome sections. The uppermost basalt, universally presenthe areas I have mapped, occurs at or near the base othick section of sandstone that forms the upper divisionthe Unicoi. I have found it a useful criterion for mapping thcontact between the two divisions

The massive upper division of the Unicoi is the mopersistent stratigraphic unit of the Chilhowee in this area ais most useful as a mapping unit. The sandstones are tcally maroon crossbedded arkoses. Maroon colors are common toward the top of the formation and some of thehigher greenish-gray beds may be equivalent to arkosic sstone included by King and Ferguson (1960) in the lowpart of the Hampton Formation.

Hampton and Erwin Formations — The Hampton and Erwin Formations are composed of the same rock types aare very difficult to differentiate unless there is continuousexposure. They consist of dark clay shale, siltstone and sstone. The sandstone is in general better sorted and contless clay matrix than that in the Unicoi. Vitreous quartzitesare fairly common but certainly not dominate. The HamptoFormation contains a higher percentage of shale than theErwin and is commonly separated from the Erwin by a masive quartzite at the base of the latter.

Shady DolomiteThe Shady Dolomite of Early Cambrian age is the lo

est of the carbonate units that characterize the Appalacmiogeosyncline below the Middle Ordovician clastic wedg(King, 1959). It consists of light blue, gray or white dolomitwith lesser amounts of limestone and carbonatic shale. InMt. Rogers area it is about 1,000-feet thick. Fossils are raThe Shady Dolomite is commonly blanketed with charactistic dark-red or red-brown sticky residual clay that is hostmanganese deposits.

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Rome FormationThe Rome Formation of Early Cambrian age is t

youngest bedrock unit in the Mt. Rogers area southeasthe Holston Mountain fault. It consists of maroon, gray, green silty shale with lesser amounts of sandstone and sdolomite. Carbonate is commonly present in the clasrocks. Much of the unit is highly deformed. King and Fergson (1960) report that the Rome Formation is 1,250 to 1,8feet thick in the Mountain City-Damascus area. Fossils rare.

Southeast flank of the Anticlinorium

Amphibolite and Mica Gneiss and SchistKeith (1903) used the names Roan Gneiss and Caro

Gneiss for amphibolite and layered mica gneiss and schrespectively, in northwestern North Carolina. These namhave been abandoned by the US Geological Survey becathey were applied widely throughout the southern Appachians to lithologically similar but not necessarily correlativrocks (Bryant, 1962; Brobst, 1962). These rocks remawithout a formal name here. They are interpreted as mmorphosed interbedded and interfingering mafic volcan(amphibolite) and clastic sedimentary rocks (mica gneiss schist) forming a stratigraphic unit whose thickness mustmeasured in miles.

Some mafic rocks are coarse grained and have regabbroic textures; these are probably penecontemporaneshallow intrusives. The bulk of the mafic rocks, however, afine grained and occur in layers, that range in thickness frless than an inch to hundreds of feet and that are confoable with compositional layering in the mica gneiss anschist. These were probably lava flows and tuffs. Some figrained mafic rocks contain tabular pseudomorphed plagclase phenocrysts (now largely mosaics of oligoclasandesine with or without clinozoisite and garnet) that habit closely resemble plagioclase phenocrysts in basaltthe Mount Rogers Volcanic Group. The mafic rocks are pticularly abundant in the rugged mountain terrain west asouthwest of the West Jefferson, North Carolina.

The mica gneiss and schist are metamorphosed sulfsandstone (mostly fine-grained graywacke) and grit containg shale partings and thick interbeds of shale. The sastone is locally calcareous. Bedding is variable. Most beare less than a foot thick but sandstone beds one to twothick are common and 10-foot beds are found in places. Bgraded bedding and crossbedding are rare.

In Ashe and Watauga Counties, North Carolina, therocks are in the staurolite-kyanite grade of regional memorphism. The mafic volcanic rocks are amphibolites agarnet amphibolites. The sedimentary rocks are dominanfine-grained biotite-muscovite gneisses, commonly sulfidand with or without garnet. Pelitic rocks are commonly starolite-kyanite-garnet schists.


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From evidence obtained near Galax, Virginia, thamphibolites and mica gneisses and schists rest nonconfoably upon the Cranberry Gneiss. They are thought to belate Precambrian age and correlative at least in part withMount Rogers Volcanic Group and the Lynchburg Gneisscentral Virginia (Rankin, 1967a).

ROAD LOG

The field trips Saturday and Sunday will be entirewithin the Winston-Salem 1° x 2° quadrangle (sca1:250,000). The following 7¾-minute quadrangles will beuseful:Saturday

Abingdon, VA.Damascus, VA.Konnarock, Va.*Grayson, Tenn. – N.C. – VA.*Park, N.C. – Va.Whitetop Mountain, VA.*

SundayLaurel Bloomery, Tenn. – Va.Mountain City, Tenn. *Baldwin Gap, N.C. – Tenn. *

*Stops will be made in these quadrangles. In addition, thewill be some stops in parts of the Cranberry 30-minute quadrangle for which there are no published 7¾-minute quadrangles.

Saturday, October 14, 1967

Buses will leave from in front of the Martha WashingtoInn, Abingdon, Virginia, at 8:00 A.M.

Mileage

0.0 Buses leave Martha Washington Inn (elevation 2,09feet) heading northeast on US 11 (main street Abingdon). From Abingdon to Damascus our routakes us across the Appalachian Valley, here underlmostly by various carbonates of the Conasauga aKnow Groups of Middle Cambrian to Early Ordovician age, but including synclines of Middle Ordovcian rocks dominated by clastics. I am not familiwith these rocks and will not try to describe themStructurally these rocks are in the Pulaski fault bloci.e., above the Pulaski thrust fault. Twenty miles or to the northeast the Pulaski fault cuts rocks as youas Mississippian. (See Virginia Division of MineraResources, 1963). The next higher tectonic unit, tShady Valley thrust sheet, involves rocks only ayoung as Middle Ordovician and is in turn overriddeby the Blue Ridge thrust sheet. What is the age movement of the Blue Ridge thrust sheet?

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2.6 Underpass, Interstate 81. Approaching the underpassa clear day, Mt. Rogers and Whitetop Mountain mbe seen over Iron Mountain (held up by the Chhowee Group) more or less straight ahead.

3.0 Junction of US 11 and US 58. Turn right toward Daascus.

5.5 Bridge over Middle Fork Holston River. Elevatio1,791-feet, lowest point on trip.

9.9 Bridge over South Fork Holston River.

12.5Damascus corporate limit.

13.0Roadside ledges right, on curve of Rome Formation.

13.4Follow US 58, right-angle turn left across Norfolk anWestern Railroad tracks and across bridge over Bverdam Creek onto the main street of DamascExposures of Shady Dolomite in Beaverdam Creunder bridge are the last exposures below the HolsMountain fault. After passing through Damascus wleave the relatively open country of the AppalachiaValley and enter the mountainous Unaka and BluRidge provinces.

13.9Follow US 58 around a right-angle turn right, and thshortly around right-angle turn left, all within thetown of Damascus.

14.3Exposures at top of bank on left of sandstone in upper division of the Unicoi Formation. We are nowabove the Holston Mountain fault and in the ShadValley thrust sheet.

15.0Bear left on US 58 at Junction with VA 91. Note cationary road sign. Here and for the next ¾ mile, expsures on left are the Hampton Formation. Hydroiron sulfate efflorescence on some surfaces.

15.9Sharp curve left. Exposures on left and all exposuresnext 1.7 miles around several sharp turns are of upper division of the Unicoi Formation. The ShadValley thrust sheet has been folded into a synclicalled the Stony Creek syncline by King and Fergson (1960). In Johnson County, Tennessee, to thsouthwest, the syncline is broad and open and loccarries Shady Dolomite and Rome Formation in itrough (Figure 2). Typically more than five miles searates the top of the Unicoi Formation on opposlimbs. To the northeast in Virginia, the syncline ismuch tighter, commonly asymmetric, and in placethe southeast limb is overturned. Typically a mile oless separates the top of the Unicoi on opposite limand the youngest unit exposed in the trough is tErwin Formation. There are also structural basialong the synclinal axis caused by slight variationsthe direction of plunge of the axis. Our route acrothe Shady Valley thrust sheet crosses a sad

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between two structural basins. We are here abouthe trough of the Stony Creek syncline and near tnortheast end of the Sutherland basin of King and Fguson (1960). Bedding dips very gently west.Whitetop Laurel Creek, the stream on the right, is tonly stream between the New River and the WatauRiver, a distance of 75 miles, that cuts completethrough Iron Mountain. It is significant that it does swhere the Shady Valley thrust sheet is narrowebecause of the high saddle in the trough.

17.6High cut on left is the last exposure here of the updivision of the Unicoi. Bench mark 2,214-feet in thsouthwest corner of the Konnarock quadrangle between the road and Whitetop Laurel Creek. Jahead on far side of stream are exposures of chewup basalt followed by quartz pebble conglomerate the lower division of the Unicoi.

17.9Exposures, left, or alternating thin beds of sandstand shale of the Hampton Formation, also containa 20-foot quartzite bed. We have now re-crossed Holston Mountain fault and are in a fairly large fauslice northeast of Damascus made up of Unicoi aHampton that is structurally between the Shady Vley thrust sheet and the Appalachian Valley (Figuresand 2).

18.2Picnic tables on right, exposures of more shaly Hampon left. The road now leaves Whitetop Laurel Creeand follows a tributary called Straight Branch (surean attempt at humor by the mapmakers). The railrofollows Whitetop Laurel Creek. We shall rejoin therailroad 700-feet higher in about 9 miles.

18.6First of many bridges over Straight Branch.

18.8Re-cross Straight Branch on sharp curve. Exposuleft, inside curve are tightly folded sandstones in tupper Unicoi. (Still in large slice below HolstonMountain fault). Folds overturned to the northwest. takes considerable imagination to see these folds fra moving bus, but they are there. On slope above riside of stream at bridge are ledges of quartz pebconglomerate of the lower Unicoi. These are in thShady Valley thrust sheet. Therefore, the HolstoMountain thrust fault passes through the bridge.

19.0Road cut on left in the Upper Unicoi in slice below Hoston Mountain fault.

19.2Exposures on left are grit of the lower Unicoi above tHolston Mountain fault. We have now finished playing hide-and-seek with the Holston Mountain fauand will be in the Shady Valley thrust sheet for sevemiles.

19.4Road cuts on right and ledges in stream on left of basseparating the upper and lower division of the Unico

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There are two basalts here separated by about 45-of crossbedded sandstone. The lower basalt is ab50-feet thick and the upper basalt is about 70-fethick. Amygdules are abundant in the upper part each basalt. Most workers have thought that thebasalts are lava flows. (See King and Ferguso1960). I have seen no diagnostic features.

20.0Highway sign indicating mileage to Independence. Fthe next 0.7-mile there is almost continuous exposuof sandstone of the upper Unicoi dipping about 20ESE. We are on the northwest limb of the Stony Cresyncline. Cliffs of this sandstone are visible on thridge ahead.

20.3Sharp curve to right and massive white crossbedquartzite in the upper Unicoi. Enter narrow part gorge cut in upper Unicoi.

20.7Top of gorge.

21.3Sharp curve right at BM 2,874-feet on the Konnaroquadrangle. Ledges of upper Unicoi.

21.4Road left to Feathercamp Lookout Tower from whicthere is an excellent view.

21.5Exposures in stream on left at sharp bend to left arsandstone and shale of the Hampton Formation, asall exposures for the next mile.

22.5Cross small fault that cuts out the Hampton on southeast limb of Stony Creek syncline. Exposuresright are of the upper division of the Unicoi Formation.

22.6Bear Tree Gap, elevation about 3,050-feet, on the cof Straight Mountain (the southeast ridge of IronMountain. Exposures on left of crossbedded sanstone of the upper Unicoi overturned to northwest. Ware now on the southeast limb of the Stony Creek scline. Saprolite of the upper basalt is exposed in rocut about 200-feet east of gap. View: Prominent highmountain straight ahead with open fields on right siis Whitetop Mountain, elevation approximately5,530-feet, where we will have lunch. Partly visible the left of this is the rounded, wooded Mt. Rogerelevation 5,729-feet. The low country between BeTree Gap and Whitetop Mountain is underlain mostbe sedimentary rocks in the upper part of the MouRogers Volcanic Group and is drained by WhitetoLaurel Creek, the same stream we were following elier. The wooded ridges to the right, across WhitetoLaurel Creek are held up by the Chilhowee Group intectonic unit above the Shady Valley thrust sheet.

22.8Sharp curve right. Exposures of the two basalts in Unicoi followed by many deeply weathered exposures of the lower division of the Unicoi Formatiocontaining many beds of quartz pebble conglomera

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Bedding dips steeply northwest or is overturneThese road cuts continue for 0.7-miles around sevesharp curves.

23.5 - More Curves. The contact between rusty weatherquartz pebble

23.7conglomerate of the lower Unicoi and maroon tillite anshale of the Mount Rogers is crossed three times. Tcolor change should be obvious even from the bus athe middle of the three contact localities may be easlocated exactly by digging.

24.2Spectacular exposure on left of fresh maroon matrix lite in more weathered laminated shale and sandstoMount Rogers Volcanic Group. If time permits, wemay stop here on the way back this afternoon.

24.5Side road right to Creek Junction, one of the best plato see large scale faulting. Long road cut on left upper maroon sedimentary rocks of the Mount Roers. Some rocks are calcareous.

24.9Exposures on left are tillite. Turn right onto dirt road(Co. Rd. 600) and cross Whitetop Laurel Creel (Fiure 3). This is an old railroad bed.

25.1Long strike ledge on left of sandstone in the MouRogers. Beds are overturned and dip 45× SE. We now stratigraphically below the lowest tillite.

25.3 - Scatter roadside exposures of maroon shale, rhythmand pebbly rhythmite in

26.1The upper part of the Mount Rogers.

26.1Approximate location of the Catface thrust fault thcarries a large fault slice beneath the Blue Ridthrust sheet over the Shady Valley thrust sheet. Hsandstones of the upper division of the Unicoi Formtion override maroon sedimentary rocks of the MouRogers.

26.2Road cut on left is in the Hampton Formation.

26.3Sheared quartz pebble conglomerate of the lower Unin fault contact with Hampton. The Unicoi is here in different small tectonic slice (Figure 3).

26.4Beginning of a long stratigraphic section in the larslice above the Catface fault that begins here in tErwin Formation and continues without repetitiodown through the Hampton and Unicoi and into thupper sediments and then rhyolites of the Mount Roers Volcanic Group. The section contains sevethousand feet of rock and is inverted. In places, pmary sedimentary features in addition to gross stratraphy demonstrate that, although beds dip southetops are to the northwest.

26.6Long cleft-like cut blasted through the Erwin; beddinmarkedly overturned. The next several exposures

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27.0Exposures on left of shaly Hampton.

27.1Prominent sandstone rib marking the top of the UniFormation.

27.3STOP 1: Country Road 600 crosses the West Jeffersbranch of the Norfolk and Western railroad and boroad and railroad cross Green Cove Creek. Leabuses and walk about one-mile along railroad. Buswill move ahead to the terminus of our walk. Anexcellent section from the upper Unicoi down to thhighest rhyolite in the Mount Rogers is exposed alothis stretch of the railroad. The letters below refer letter locations on Figure 3.

(a)A resistant, steeply dipping sandstone bed in upper division of the Unicoi Formation forms thnorth abutment of the highway bridge and continuas a rock rib up the steep slope of Lost MountaBedding dips 75× SE (upstream) but crossbeddingthe rocks under the bridge indicates that the beds overturned. Note peculiar series of funnel shapdepressions on the bedding surfaces. Does anyhave a good explanation for them? Maroon arkoand grit with interbedded maroon shale is exposedroad cuts on the south side of the highway bridgKing and Ferguson mapped these as rocks of Mount Rogers Volcanic Group probably because their prominent maroon color. Their interpretatiowas that the Catface fault forming the southeast fraof the Mountain City window separated these rocfrom the upper Unicoi inside the window on the nortside of the highway bridge. My interpretation is thathat the maroon rocks south of the highway bridge aupper Unicoi and that there is no fault here. Note tdetrital micas on the bedding surfaces of the shaThese are characteristic of maroon pelitic rocks in tUnicoi but are unknown in maroon pelitic rocks of thMount Rogers. Hence, even tiny shale or slate chin the soil may be used as a mapping criterion. Thare excellent loose pieces of maroon crossbeddarkose on the streambank here.

(b)Scattered exposures of upper Unicoi along the raroad.

(c)Two amygdaloidal basalts separated by 3-feet arkose mark the top of the lower division of the Uncoi here. The upper basalt is about 55-feet thick aabout 50-feet of the lower basalt is exposed along ttrack. The contacts of the basalts are sheared andnot possible to demonstrate whether they are flowspenecontemporaneous sills.

d)Series of exposures of the lower division of the Ucoi Formation. Quartz pebble conglomerates exhi

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rusty weathering and contain interbeds of maromicaceous shale and fine green sandstone. Crossding confirms that although the beds dip steepsoutheast, tops are to the northwest. The lower Uniis about 600-feet thick here, including the basalts.

(e)Contact between quartz pebble conglomerate of Chilhowee Group and tillite of the Mount Rogers Volcanic Group. Bedding in the Unicoi is parallel to thcontact. The tillite is not bedded and is not particlarly impressive in these stained railroad cuts. Hoever, just ahead (south) and to the right along GreCove Creek are large blocks of both quartz pebbconglomerate from the Unicoi and tillite from theMount Rogers. The contrast between the two rotypes is striking and surely connotes either a diffeence in source area or climate in the source areaboth. A count of clasts 0.2-inches or more in thsmallest exposed dimension in conglomerate of thUnicoi at this locality shows that 90 percent of theare essentially monomineralic (bull quartz, pink feldspar and black chert) and 10 percent of them are rfragments. Three out of four clasts are bull quartz athey reach a maximum length of about 4-inches. contrast, 95 percent of the clasts in the tillite at thlocality are rock fragments, the size range is greaand the clasts are less rounded. Much may be learfrom even a quick study of the rock fragments in bothe conglomerate and tillite. First, clasts of rocksdemonstrably from the Mount Rogers Volcanic Grouare universally present in the tillite. Here, thesinclude porphyritic and nonporphyritic rhyolite,greenstone, and maroon pelite, and they constitabout 14 percent of the clasts. The presence of a percent of similar clasts in the conglomerates of tlower Unicoi should not require an unconformityabove the Mount Rogers (see King and Fergus1960, p.31). Second, granitic rocks dominate thclasts in the tillite and these clasts are either nonfoated or have a crude foliation subparallel to the foltion in the matrix of the tillite. There are no clasts the typical flaser gneiss and augen gneiss that mup the Cranberry Gneiss beneath the more higsheared basal parts of the mount Rogers to the soeast. The cataclasis of these basement rocks, thfore, took place in Phanerozoic time. Many of thgranitic clasts are porphyritic, containing large phnocrysts of pink feldspar. This supports the concethat augen gneisses in the Cranberry formed from shearing of porphyritic granitic rocks. Finally, therare very few clasts of metamorphic rocks (schist agneiss) in the tillite. Note that the matrix of the tillitsurrounding many mafic clasts is greenish, indicatian exchange of oxygen between clasts and matrix d

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(f)Cross Star Hill Branch on trestle. Arkose below thlowest tillite crops out just upstream.

(g)Exposure of arkose; Mount Rogers VolcanGroup.

(h)Float and scattered outcrops of porphyritic weltuff that constitutes rhyolite A, the upper of the threrhyolites in the middle of the Mount Rogers VolcanGroup. The lower two have not been found in ththrust sheet. Collapsed pumice fragments are visiin some thin sections from this vicinity.

(h)Green matrix conglomerate stratigraphically aborhyolite A. Ford stream here and walk a couple hudred feet south along road to junction with side roto Taylors Valley. The buses will be waiting at thintersection.

(j)Roadcut in rhyolite A – This is the same belt orock that is exposed on the hills near locality (above, but here it is more sheared and harder to difentiate from sheared arkose and graywacke. This icommon problem. Typically sheared remnantembayed quartz, and patch perthite phenocrysts recognizable in thin sections of sheared rhyolite even those that are sericite phyllites. Where there isadmixture of detrital material, e.g., plutonic microcline, the problem becomes a semantic one.

For those that have a chance to return someday,only unequivocal basaltic pillow lava I have seen the Mt. Rogers area is exposed in a railroad cut ab¼ mile southeast and around the bend of the railroBoard buses and we will retrace our route out CounRoad 600 to US 58.

31.5Turn right onto US 58 at intersection.

31.9Follow US 58 around right-angle turn to right at inter-section with County Road 603.

32.1Exposures on left of maroon rhythmite in the upper pof the Mount Rogers Volcanic Group but below thtillite. You will recall that we have now crossed bacinto the Shady Valley thrust sheet.

32.2Exposures on left, or rhythmite and arkose of the MoRogers.

32.7Cross unexposed Catface fault into large fault slicbetween Blue Ridge and Shady Valley thrust sheets

32.9Road cuts on right are quartz pebble conglomeratethe lower division of the Unicoi Formation.

33.0STOP 2: Conformable contact between the Unicoi Fomation and the Mount Rogers Volcanic Group on BHill. Buses will park in large turnout on right side oroad on outside of large curve concave to left. Wa

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ahead 400-feet around curve to right to contacWATCH OUT FOR TRAFFIC. Between the busesand the contact are exposures of rusty-weatherquartz pebble conglomerate and arkose of the lowUnicoi. Conglomerate beds are mostly one to 3-fethick, but some are as thick as 8-feet. Arkose beds generally thinner. Again, most clasts in the conglomerates are quartz pebbles and average 0.5 to 1-inclength. The largest one observed here is about 4inches long. Fragments of single feldspar crystals large as 1-inch occur sparingly. Note that where twquartz pebbles are in contact, one commonly indethe other, presumably a solution phenomenon. Thlower 50-feet or so of the Unicoi (around corner tright) consists mostly of feldspathic grit, but includea bed 1.5-feet thick of quartz pebble conglomerateits base. This basal bed is atypical in that it containhigher percentage of small granite pebbles. The ctact is knife sharp and although the Virginia Deparment of Highways has not aided the visiting geologby their enthusiastic grass planting, the contact mstill be uncovered by a little digging. The 1.5-foothick bed of Unicoi quartz pebble conglomerate herests on maroon laminated clay shale and arkosethe Mount Rogers. Beds on both sides of the contdip 60° N. The laminated shale and arkose lack obous graded bedding and are hence not the typrhythmites. One graded bed was observed a finches below the contact and it confirmed that toare to the north. Several feet from the contact, tMount Rogers beds are folded locally. Such deformtion is certainly to be expected in incompetent bedsthis sort beneath thick conglomerates. Maroon tillicrops out about 100-yards up the road. Continue road as far as the tillite and then return to buses. Kand Ferguson (1960, p.31) concluded that this ensection on Big Hill was in the Mount Rogers VolcanGroup and called attention to the similarity of somethe arkoses and conglomerates on Big Hill to thosethe lower division of the Unicoi Formation. The latteobservation is quite correct! The contact we crosson big Hill is the same contact we crossed on the raroad at STOP 1 and in fact has been traced to it. Obus route on US 58 takes us across the contact at more points between STOPS 2 and 3. However, additional stops are planned to observe it.

33.3Crest of Big Hill and sharp turn right of US 58. Loexposures on right of tillite. The high mountains visble ahead just before rounding the bend are Bee(right) and Whitetop (left), the location of our nexstop.

33.8Road cut on left of quartz pebble conglomerate in tlower division of the Unicoi. The road has turne

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back on itself enough so that we have re-crossed contact at the base of the Unicoi.

33.9Summit Cut. Bedding dips 35× E and is overturned. Dslope on right is feldspathic grit in the upper divisioof the Unicoi. Red-brown saprolite on left is basaUnweathered spherical remnants of basalt protrufrom the saprolite. Beds of quartz pebble conglomeate of the lower division of the Unicoi crop out at thtop of the cut on left. Numerous exposures of lowUnicoi continue on left to bottom of hill.

34.3Open field on left. Foot of alluvial fan coming dowfrom Beech Mountain. Most of the material in the fahere is rhyolite C of the Mount Rogers VolcaniGroup that caps Beech Mountain.

34.9Exposures on left of the lower division of the UnicFormation. Cross unexposed contact between the Ucoi and Mount Rogers in stream valley. Tillite iexposed in ditch beside road on far (south) side stream. The railroad along Green Cove Creek (ST1) is only about a half-mile downstream to the right.

35.1Low roadside ledges and float of maroon pebbly rhymite.

35.8Side dirt road on right. Rhyolite A of the same unit viited in STOP 1 crops out in the valley to the righThere are poor exposures of greenstone in the rcuts ahead – probably the same pillow basalt expoalong the railroad on Green Cove Creek.

36.4Green Cove Church. Follow US 58 around right-anturn to left.

36.8Roadcuts on right of another flow unit of rhyolite AJust ahead is a quarry on right in rhythmite. Peliparts are slates.

37.6Exposures on right of rhyolite A as are all exposures the next half mile.

38.1Whitetop Gap, elevation about 3,680-feet, on the divbetween the Tennessee (Holston) and Ohio (Nedrainages. Follow US 58 around sharp turn to leExposures of laminated slate (rhythmite) just aheon right. For the next 2.5-miles exposures are poor detailed mapping shows that these rocks are rhythmand rhyolite A in the upper part of the Mount RogerBedding generally dips gently north under WhitetoMountain and is right-side up.

38.5Settlement of Park for which the 7¾-minute quadranis named. View of Whitetop Mountain above us to thleft.

40.5Turn left onto dirt road up Whitetop Mountain.

41.4Ledges on right of rhyolite C, the lowest of the thrrhyolites that made up the middle of the Mount Roers Volcanic Group. We have now crossed a rat

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poorly located fault that by my interpretation is thStone Mountain fault. We are now in the Blue Ridgthrust sheet.

42.4Quarry on right in rhyolite C.

42.6Take left fork of road in saddle by Bluff Mountain(toward Whitetop Mountain).

43.1Approximate contact between rhyolite C and overlyirhyolite B. Ledges of both are exposed in propsequence in woods to left. The road remains in rhylite B to the summit of Whitetop Mountain.

44.4Toll gate.

45.8STOP 3. Picnic area just west of the summit ofWhitetop Mountain. Lunch. Please leave no refuseon the ground. After lunch, walk about ¾-mile downover rough open field to Buzzard Rock. Our lowepoint will be about 400-feet below the buses. Jetransportation can be provided most of the way fthose who need it. Use caution in walking down ovfield. There are many rocks and holes hidden in tgrass. If the grass is wet, the walk can be treacheroIn any kind of decent weather the views are supebut don’t try to look at view and walk at the samtime. The letters below refer to letter location on Fiure 3. For reference the saddle between Buzzard Rand Whitetop Mountain is assumed to be an elevatof 5,100-feet.

j.Buzzard Rock area. Numerous outcrops of rhyolitewhich contains a few percent phenocrysts of reddperthite and greenish-white plagioclase.

k.Elevation about 5,040-feet. Intimate mixture of grnitic basement fragments and volcanic material, proably representing local reworked material on thbasement. The strong subhorizontal foliation obscutextural relations.

m.Elevation about 4,980-feet. Nonconformity at baof the Mount Rogers Volcanic Group. The contact not exposed but ledges of volcaniclastic rocks of tMount Rogers are only 35-feet horizontally fromledges of granitic Cranberry Gneiss. The Cranbehere is a strongly foliated medium-grained falsgneiss roughly of quartz monzonite compositionThere is no remaining primary dark mineral here. addition to sheared and fragmented quartz, microcland plagioclase, the rock contains chlorite, epidoabundant sericite and minor stilpnomelane. Rathoddly there is no prominent lineation here. Abou300-feet downhill from here are ledges of tillite. Whais going on?

n.Recross nonconformity (not exposed) betweCranberry Gneiss and rhyolite C. Note that there ano volcaniclastic rocks here at the base of rhyolite

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j.Buzzard Rock. Discussion of various geologimegafeatures visible from here. Beech Mountaiacross the saddle from Buzzard Rock, is cappedrhyolite C. Tillite underlies rhyolite C on the west sidof Beech Mountain and tillite underlies the CranberGneiss both north and south of the saddle betweBeech Mountain and Buzzard Rock. Where stratifirocks are associated with the tillite, bedding diunder rhyolite C and the Cranberry Gneiss. The tillion the slopes of Beech Mountain may be tracaround the nose of the anticline and is continuous inthe tillite underlying the Unicoi on Green Cove Cree(STOP 1) and Big Hill (STOP 2). A low-angle faulmust separate the tillite below from the CranberGneiss and rhyolite C on Beech Mountain anregional mapping has shown this fault to be the StoMountain fault forming the sole of the Blue Ridgthrust sheet.

O.Ledges of rhyolite C.

p.Ledges of breccia containing fragments of gran(sparse), rhyolite C, and rhyolite B in a matrix of phenocryst-poor rhyolite. This is a basal breccia of rhylite B.

q.Scattered outcrops of rhyolite B. Most of these arather featureless.

r.Lower road loop and picnic table. Tuff breccia inrhyolite B. Note that on some surfaces the fragmennature of the rock cannot be seen. This tuff brecciaprobably ash-flow material continuous with ash-flotuffs well exposed on the east shoulder of WhitetMountain. The ash-flow sheet can be traced to soextent around the south side of Whitetop Mountabut attempts to trace it around the north side of tmountain have not met with success.

s.Diabase dike about 150-feet wide cutting lava flowof rhyolite B. In thin section ophitic or subophitic texture is still visible between plagioclase (strongaltered to sericite and clinozoisite) and clinopyroxenActinolite, clinozoisite in larger grains, chlorite anleucoxene are secondary minerals. This dike has btraced about 0.4-miles across the mountain. Rhyoon both sides of the dike has chaotic flow banding ahence is lava. There are scattered outcrops of lavrhyolite B from here to the summit of the mountain.

RETURN TO BUSES

The following locations on the way down are noted ffuture visits. We will not stop at them today.

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u.Rhyolite B containing lithophysae as large as 2inches across and containing as many as 40 shells.

v.Numerous exposures of welded tuff in rhyolite B.

49.0Road junction in saddle by Bluff Mountain.

Turn sharp left (150°) toward Elk Garden.

50.4 STOP 4:Elk Garden. This stop is conditional upon geting the landowner’s permission. Should we stop, donot climb fences and do not chase cows. Dividebetween Holston and New River drainages. Wathrough gate to outcrops of greenstone in the lowpart of the Mount Rogers Volcanic Group. Whatevthe structure here, it is not simple. In the valley to tsouth, the greenstone is in contact with CranbeGneiss, and near the contact, the greenstone and aciated graywackes contain fragments of Cranberry. the north down the slope of Elk Garden Ridge, ocrosses successive belts of graywacke grit, rhyoliteand rhyolite B. Foliation dips southeast. Across throad beyond the buses are outcrops of rhyolite B. Minterpretation is that the Stone Mountain fault seprates the greenstone in Elk Garden from Rhyoliteacross the road (see Figure 2). The greenstone is of an overturned limb of a large recumbent fold in tectonic slice below the Stone Mountain fault buabove the Shady Valley thrust sheet. Because stratigraphy of this slice is different from that alonGreen Cove Creek, it is probably a different slice. Tgreenstone here contains albite, epidote, chlorite, lcoxene and magnetite. Some contain actinolite asome contain relicts of clinopyroxene and small lathshaped phenocrysts of plagioclase. Locally magneis abundant enough to render a compass useless the Elk Garden area is the locus of a very pronouncpositive anomaly found in an aeromagnetic survey southwestern Virginia (Issacs, 1962). The greenstoalso contains veinlets of epidote and quartz and knof various combinations of epidote, quartz, calcite achlorite. The knots are probably amygdules. Stragraphically overlying graywacke grit containingmany volcanic and some granitic clasts crops out nethe north edge of the pasture.

53.0Cross probable thrust fault into the tectonic slice wwere in at STOPS 1 and 2. Exposures are poor but of arkose and rhythmite below the tillite. The thicmass of rhyolite A is missing between the arkose arhythmite and rhyolite B forming most of the northslope of Whitetop Mountain. This is the principal reason for suggesting a fault here.

53.3Cross Big Branch and descend surface of large allu

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54.5Elk Garden road dead ends into County Road 603.

STOP 5: Junction of County Roads 600 and 603 on nortside of bridge over Big Laurel Creek (Whitetop Larel Creek of earlier in day). Pebbly rhythmite in thupper part of the Mount Rogers is exposed in a smroad material quarry here. We are probably still in thtectonic slice above the Shady Valley thrust sheet bthat is very difficult to demonstrate. Certainly rocksquarter of a mile north of us are in the Shady Vallesheet and pass upward through tillite to the base of Unicoi Formation at the foot of the steep slope of IroMountain. Note the graded bedding with coarser comonly greenish siltstone bottoms grading up into finmaroon tops. Some thin coarser bottoms are vpoorly sorted, containing coarse and granule-sclasts. In addition, larger pebbles are scatterthroughout the graded beds. Elsewhere in this valthese clasts reach a maximum of 1-meter in diameIf there were only a few of these dropped pebbleswould be happy to ignore them but they are all ovthe place. Because most of them are granitic, itunlikely that they were emplaced by volcanism. Msuggestion is that these are varved sediments depited in a lake that was ice covered annually. Note athe evidence for soft-sediment deformation, perhaslumping on the lake bottom. Some arkose beds ctain randomly oriented slivers of maroon shale.

55.0Contact between rhyolite A and overlying maroorhythmite and arkose. This outcrop is certainly bacin the Shady Valley thrust sheet.

56.4Community of Konnarock. Once the site of a large samill and logging operation. Exposures of rhythmitand arkose on right.

56.8Exposures of tillite on right.

57.4Intersection with US 58, our route this morning. Cotinue on USS 58 back to Abingdon for the banquand annual meeting.

82.7Martha Washington Inn, Abingdon, Virginia.

Sunday, October 15, 1967

Transportation today will be by automobile and we wbe about 50-miles from Abingdon by noon. For most of yoit will be much out of the way to return to Abingdon, scheck out before leaving. Because some have expresinterest in spending more than half a day the trip will cotinue informally in the afternoon. Anyone wishing to spenmore than half a day should bring a lunch and others mwish to have a snack along because restaurants are spanorthwestern North Carolina.

Departure time from the Martha Washington Inn

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0.0 Martha Washington Inn. Retrace yesterday’s route US 58 through Damascus to Junction with VA 91.

15.0Turn right on VA 91 headed for Mountain City.

15.9Ledges of the upper division of the Unicoi Formation,are all ledges for the next mile. For reorientation ware in the Shady Valley thrust sheet on the northelimb of the Stony Creek syncline.

16.7Virginia -Tennessee line.

16.9Exposures of the higher of two basalts in the Unicoi.

17.0Exposures of the lower of two basalts of the Unicoi, folowed by ledges of the lower division of the Unicofor the next two miles. Quartz pebble conglomeraare readily identifiable.

19.0Outcrops of Unicoi quartz pebble conglomerate in smstreams on left. Slopes above on left are FodderstMountain which is underlain by the Mount RogerVolcanic Group, as is the northeastern end of StaRidge to the right. The Mount Rogers thins to a feateredge on Stack Ridge, and farther southwest lower division of the Unicoi rests on CranberrGneiss. Cross unexposed Iron Mountain fault anenter Mountain City window. The segment of the widow we cross is mostly underlain by the Shady Dolmite and the Rome Formation in a rather broad opvalley.

19.4Exposures on left of the Rome Formation, as areexposures for the next 4.8-miles.

21.0Community of Laurel Bloomery, Tennessee.

24.2Exposures on left of the Shady Dolomite. Note the asciated dark red-brown residual clay.

26.4Exposure on left of the Rome Formation.

28.7Traffic light in center of Mountain City, TennesseContinue straight.

29.3Intersection with US 421. Bear left on US 421 towaBone.

Use caution.

Sharp ridge on far side of US 421 is held up by thErwin Formation, part of the complex much-faulteuplift of the Doe Ridges (King and Ferguson, 1960)

31.3Exposures on left of the Rome Formation.

31.8Hermit Motel.

32.5Turn left off US 421 onto unmarked paved road. Exposures of Shady Dolomite.

32.7Pavement ends; bear right.

32.8Inactive quarry in Shady.

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33.5Water-filled quarry in Shady33.6Dirt road dead ends into paved road. Turn right toward

Payne Gap.

Cross Stone Mountain fault and enter Blue Ridge thrsheet above the Mountain City window.

33.7Exposure on left of the Cranberry Gneiss.

34.4Ledges of white quartzite of the Erwin Formation oright exposed in a small window through the BluRidge thrust sheet. Ridge visible to north is ForgMountain, held up by Chilhowee Group on the souteast side of the Mountain City window.

34.7Ledges of Cranberry Gneiss on right (back in the BlRidge thrust sheet).

35.4Excellent exposures on left of little sheared quamonzonite of the Cranberry Gneiss. Some is porphritic with microcline phenocrysts up to 1.5-inchelong.

35.7Forge School on right.

36.4STOP 6: Parking space is limited here; please use astle as possible. Cranberry Gneiss (quartz monzoncut by porphyritic greenstone dikes. Walk up roadabout 0.4-mile past almost continuous exposuMuch of the Cranberry here is massive fine-grainquartz monzonite (subequal amounts of microclinand sericitized plagioclase). The primary dark mineris biotite, now altered to chlorite and epidote, whicconstitutes 5 to 10 percent of the rock. There is aquite a lot of medium-grained quartz monzonite wipink microcline phenocrysts as much as an inch oracross. Note the pegmatitic clots. These probably dfrom the time of formation of the Cranberry Gneisrather than Paleozoic metamorphism. The Cranbeis cut by porphyritic mafic dikes. Plagioclase phenorysts (badly saussuritized) in one dike are as large ax 0.2-inches on the surface. The groundmass mineogy is now albite, epidote, chlorite, actinolite-tremolite, leucoxene and pyrite. I have seen no pyroxenrelicts here, but I have seen them elsewhere in comrable mafic dikes cutting low-grade CranberryAssuming that the dikes are of late Precambrian athese rocks have not been metamorphosed beylow grade in Phanerozoic time.

37.9STOP 7: Again parking space is limited. Don’t bepiggy. Fault sliver of Unicoi in Cranberry GneissThis kind of an outcrop keeps the geologist on htoes. How many like it do we miss? The layer oquartz pebble conglomerate is 15 to 20-inches thand is bordered above and below by flaser gneissthe Cranberry. All rocks have a strong foliation dipping about 35× SE. Quartz pebbles in the conglom

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ate are both flattened and elongated down the dipthe foliation. The direction of elongation is parallel tthe direction of tectonic transport on the thrust fauand is hence an a-lineation. The upper end of this vley, starting about a mile northeast of here is the locof the Stone Mountain fault, on which Cranberry ithrust upon Unicoi. Apparently a branch of this faucontinues down the valley at least this far.

38.9Cross Stone Mountain fault into Mountain City windowOutcrop of quartz pebble conglomerate of the lowdivision of the Unicoi in Forge Creek on left.

39.2Outcrop of quartz pebble conglomerate of lower Unicon right. Cross Stone Mountain fault back into BluRidge Thrust sheet. Road cuts between here aPayne Gap are deeply weathered or saprolite andin flaser gneiss of the Cranberry cut by greenstoand sparse metarhyolite.

40.2Payne Gap. Enter Ashe County, North Carolina andNew River drainage. Saprolite of flaser gneiss of tCranberry.

40.9STOP 8: Cranberry Gneiss. Good exposure of mediumgrained flaser gneiss. Note the strong foliation dipping about 45× SE and the downdip lineation in thplane of foliation caused by mineral streaking. Thlineation is in the direction of tectonic transport andhence an a-lineation. The flaser gneiss is roughlyquartz monzonite in composition and is though to besheared and somewhat recrystallized equivalent of medium-grained quartz monzonite exposed at STO6. Metamorphic minerals here include biotite, stilpnomelane (minor). epidote, sericite and calcite. Auggneiss, greenstone and metagabbro are exposed innext outcrop along the road. The augen gneiss difffrom the flaser gneiss only in containing megacrysof microcline. The augen gneiss probably is a sheaand somewhat recrystallized equivalent of the pophyritic quartz monzonite of STOP 6. The greenstoand metagabbro are thought to be younger intrusivnow sheared and recrystallized, of the same age asmafic dikes at STOP 6.

The outcrops here (STOP 8) are typical of the pltonic rocks in the core of the anticlinorium over manmany square miles, from Cranberry, North Carolinto Fries, Virginia. Exposures for the next 4.7-miles avarious aspects of the Cranberry Gneiss with varyiamounts of younger mafic intrusives.

45.6STOP 9: Metagabbro with chilled contact, intrusiveinto Cranberry Gneiss. About 5-feet of the metagabro are exposed, including the lower contact, whichsubparallel with the foliation. A finer grained zoneabout 6-inches thick occurs at the base of the magabbro and is interpreted as a chilled margin. Sm

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pseudomorphed plagioclase phenocrysts occur boththe metagabbro and in the chilled margin, and granxenoliths occur in the margin. The mineralogy of thchilled margin is quartz, albite, biotite, actinolite anepidote. The actinolite is more pleochroic than thatSTOP 6. Note the downdip mineral streaking. Thmetagabbro is probably of late Precambrian or EaCambrian age.

46.7Exposure of fairly coarse augen gneiss on left. ViewThree Top Mountain (5,075-feet) ahead. This moutain is held up by amphibolite that is part of the uppPrecambrian stratified sequence on the southeflank of the anticlinorium.

48.2Junction with NC 88. Turn right and follow NC 88upstream in the valley of the North Fork of the NeRiver. Two-tenths of a mile east along NC 88 (behinus now) is exposure of garnet-bearing augen gneis

49.8Left turn on unmarked paved road at Creston.

STOP 10 at turn. Walk ahead several hundred feet on N88. Higher grade basement rocks. Augen gneiss amafic rocks. Some mafic rocks are younger than augen gneiss and presumably belong to the samgroup of late Precambrian or Early Cambrian intrsives that were exposed in STOPS 6, 8, and 9. Omafic rocks may be older. The important feature heis that the metamorphic grade is higher. Micas acoarser-grained and the mafic rocks contain megcopic hornblende.

Continue on side road across the North Fork of tNew River (one-lane bridge). Follow paved roaright and upstream at Creston Methodist Church.

50.1Pavement ends. Turn left up side valley of Three TopCreek.

50.7Outcrops on left on far side of Three Top Creek recrystallized flaser gneiss (Cranberry).

50.9STOP 11: Pelitic schist at base of the Roan and CarolGneisses of former usage (Keith, 1903). These lered sulfidic schists and gneisses are the lowexposed rocks in this valley of the stratified rocks othe southeast limb of the anticlinorium. The minerassemblage in the schist includes quartz, plagioclamuscovite, biotite, garnet, kyanite, staurolite, tourmline, pyrite, and chalcopyrite, which places thesrocks in the kyanite-staurolite zone of regional metmorphism. Amphibolites are interlayered with thschist and gneiss a short distance ahead.

This suite of layer gneiss, schist and amphibolite cotrasts markedly with the rocks in the core of the anclinorium. By reconnaissance mapping, they habeen traced northeast to the vicinity of Fries, Virginwhere the metamorphic grade is lower, and they r

9

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End of formal field trip. For those wishing to spenmore time, we will continue up the valley of ThreTop Creek with stops to examine exposures of layemica gneiss, schist and amphibolite. Those wishingstart home from here had better consult me or somone familiar with the local geography. We are a lonway from most places! NC 88, which we left at STO10, goes to West Jefferson to the east and to TraTennessee on US 421 to the west. The dirt road upvalley on Three Top Creek crosses a 3,500-foot sadand ends at Todd on NC 194, a secondary robetween Boone and West Jefferson.

REFERENCES

Brobst, D.A., 1962. Geology of the Spruce Pine District, AverMitchell and Yancey Counties, North Carolina: US Geol. Suvey, Bull. 1122-A, 26.

Brown, W.R. 1958. Geology and mineral resources of the Lynburg quadrangle, Virginia: Virginia Division Mineral ResourceBulletin 74, 99p.

Bryant, Bruce, 1962. Geology of the Linville quadrangle, NorCarolina – Tennessee – A preliminary report: US GeologicSurvey Bulletin 1121-D, 30p.

Bryant, Bruce, 1963. Geology of the Blowing Rock quadrangNorth Carolina: US Geol. Survey Quadrant Map GQ-243.

Bryant, Bruce and Reed, J.C.Jr., 1962. Structural and metamorhistory of the Grandfather Mountain area, North Carolina – preliminary report: Am Jour. Science, Vol. 260, pp.161-180.

Carrington, T.J., 1961. Preliminary study of rhythmically layeretuffaceous sediments, near Konnarock, southwestern VirginMineral Industries Jour. (Virginia Polytech Institute) Vol. 8No.2, pp.1-6.

Davis, G.L., Tilton, G.R., and Wetherill, G.W., 1962. Mineral agefrom the Appalachian province in North Carolina and Tennesee: Jour. Geophys. Research, Vol, 67, pp.1987-1996.

Eckelman, F.D. and Kulp, J.L., 1956. The sedimentary origin astratigraphic equivalence of the so-called Cranberry and Heerson granites in western North Carolina: Am. Jour. ScVol.254, pp.288-315.

Glaessner, M.F., 1963. The dating of the base of the CambrJour. Geol. Soc. India, Vol. 4, pp.1-11.

Harland, W.B. and Rudwick, M.J.S., 1964. The great infra-Cambrian ice age: Sci. Am., Vol. 211, pp.28-36.

Hopson, C.A., 1964. The crystalline rocks of Howard and Mogomery counties In the Geology of Howard and MontgomeCounties: Maryland Geol. Survey, Baltimore, Md., pp.27-337

Issacs, K.N., 1962. Interpretation of airborne magnetometer surin southwestern Virginia for the Commonwealth of VirginiaDepartment of Conservation and Economic DevelopmeDivision of Mineral Resources; Philadelphia, Aero ServicCorp., pp. 36, fold map, scale 1:250,000.

Jonas, A.I., and Stose, G.W., 1939. Age relation of the Precambrocks in the Catoctin Mountain-Blue Ridge and Mount Rogeanticlinoria in Virginia: Am. Jour. Sci., Vol. 237, pp.575-593.

2

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dered to

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ch-s

thal

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d,ia:,

ss-

ndnd-i.,

ian:

-

nt-ry.vey,nt,es

rianrs

Keith, Arthur, 1903. Description of the Cranberry quadrang(North Carolina-Tennessee): US Geol. Survey Geol. AtlFolio 90.

King, P.B., 1955. A geologic section across the southern Appachians – An outline of the geology in the segment in TennessNorth Carolina and South Carolina, In Russell R.J., editoGuides to southeastern geology: New York, Geological SocieAmerica, pp.332-373.

King, P.B., 1959. The evolution of North America: Princeton, NeJersey, Princeton Univ. Press, 190p.

King, P.B., and Ferguson, H.W., 1960. Geology of northeastemost Tennessee: US Geol Survey Prof. Paper 311, 136p.

Laurence, R.A. and Palmer, A.R., 1963. Age of the Murray Shand Hesse Quartzite on Chilhowee Mountain, Blount CounTennessee: US Geol. Survey Prof. Paper 475-C, pp. C53-C5

Miller, R.L., 1944. Geology and manganese deposits of the GlMountain district, Virginia: Virginia Geol. Survey, Bull. 61,150p.

Neuman, R.B. and Nelson, W.H., 1965. Geology of the westeGreat Smoky Mountains, Tennessee: US Geol. Survey PPaper 349-D, 81p.

Rankin, D.W., 1960. Paleogeographic implications of depositshot ash flows: International Geol.Cong., 21st, Copenhag1960, Report, pt.12, pp 19-34.

Rankin, D.W., 1967a, Precambrian stratigraphy in the Blue Ridof Ashe and Watauga Counties, northwestern North Carol(abs.): Geol. Soc. America, Southeastern Section, ProgramAnnual Meeting, 49p.

Rankin, D.W., 1967b, The stratigraphic and structural position the upper Precambrian Mount Rogers volcanic group, VirginNorth Carolina and Tennessee (abs.): Geol. Soc. AmeriSoutheastern Section, Program for Annual Meeting, 49p.

Riecken, C.C., 1966. Level of emplacement of the Striped RoGranite pluton, Grayson County, Virginia (abs.): Geol. SoAmerica, Southeastern Section, Program for Annual Meetin40p.

Stose, A.J., and Stose, G.W., 1957. Geology and mineral resouof the Gossan Lead district and adjacent areas: Virginia DMineral Resources Bull. 72, 233p.

Tilton, G.R., Wetherill, G.W., and Davis, G.L., and Bass, M.N1960. 1,000-million year old minerals from the eastern UnitStates and Canada: Journal Geophysical Research, Vol. 654173-4179.

Virginia Division Mineral Resources, 1963. Geologic map of Viginia: Charlottesville, scale 1:500,000.

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carolina geological society

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