Geology of Dupont State Forest and the Standingstone Mountain Quadrangle, SC and NC

The 25th Annual David S. Snipes/Clemson Hydrogeology Symposium Field Trip Guidebook

Triple Falls, Dupont State Forest, NC

Field Trip Leaders: Jack Garihan and Scott Brame April 5 and 7, 2017

Overview of the Geology of Standingstone Mountain Quadrangle, South Carolina and North Carolina

John M. Garihan, Earth and Environmental Sciences Department, Furman University, Greenville, SC 20613

Introduction

Standingstone Mountain 7.5-minute quadrangle (SM) is situated within the rugged part of the western Inner Piedmont. Its southern portion lies across the North Carolina-South Carolina state line at the Eastern Continental Divide (~3000 foot elevation). The escarpment of the Blue Ridge Front winds its way across the southern margin of SM, with lines of impressive exfoliation domes (balds) formed on Table Rock gneiss. Balds that are developed on more feldspathic Henderson Gneiss are less common. The highest elevations in SM are 3600 - 3700 feet; local relief across this rugged landscape is 1400 - 2000 feet. Jones Gap State Park in South Carolina and the Dupont State Forest in North Carolina provide public access to the scenic landscape of the region via extensive hiking and horseback riding trails.

Five Paleozoic fault-bound crystalline sheets occur in the Inner Piedmont in Standingstone Mountain quadrangle (Figure 1). Stacked structurally lowest to highest, northwest to southeast, they involve: 1) Henderson Gneiss, Sheet I; 2) Chauga River Formation (muscovite-biotite-feldspar- quartz gneiss and schist, with a siltstone protolith), Sheet II; 3) Henderson Gneiss, sheet III; 4) Table Rock gneiss of the Walhalla nappe, Sheet IV; and 5) Poor Mountain and Tallulah Falls Formations of the Six Mile thrust sheet, Sheet V. Ductile thrusts lie at the base of the Six Mile sheet (Sheet V), the Seneca fault (Garihan, 2001), and at the base of Sheet II, the Eastatoee fault (Garihan and Clendenin, 2007). Good exposures of both regional thrust faults will be seen on this field trip. The Slicking Gap normal fault lies between Sheets III and IV. Geology of the area was mapped at 1:24,000 scale by Garihan and Ranson (2007) and described by Garihan (2002).

Sheet I: Henderson Gneiss

In northwest SM, muscovite-biotite-two feldspar augen Henderson Gneiss underlies a belt 1- 2 km wide along the Crab Creek drainage (Figures 1, 2). Leucocratic, poorly foliated, granitoid gneiss and pegmatite are subordinate lithologies of sheet I. Typical Henderson gneiss is saprolitic to unweathered, fine- to medium-crystalline, and well foliated. It is moderately well layered compositionally (alternating more mafic and more felsic layers) on a scale of millimeters to tens of centimeters. Rounded to ovoid to lenticular microcline augen or porphyroclasts average 0.5 – 1 cm in long dimension; they may be sparsely distributed across an exposure. Henderson Gneiss is variably mylonitic. Many pink microcline augen in hand specimen have thin, gray margins of

1 myrmekite ± fine-crystalline, recrystallized microcline. Individual feldspar augen margins in places are asymmetric (winged) as result of ductile shearing. The base of Sheet I lies outside SM quadrangle, but is inferred to be bounded below by the easternmost fault in the regional Brevard fault zone (Hatcher, 2001). We will see typical Henderson augen Gneiss of Sheet I at the Dismal Creek stop.

Figure 1. Generalized geologic map of Standingstone Mountain quadrangle, NC-SC. Sheets I-V are labeled; Sheet IV with stippled pattern is Table Rock gneiss. HGn- Henderson Gneiss, mbgn- Chauga River Formation, TRg- Table Rock gneiss, TRag- Table Rock augen gneiss, P- Poor Mountain Formation, T- Tallulah Falls Formation, sz- shear zone, diamond- sphalerite-chalcopyrite- galena prospect. Bar and ball symbol- Slicking Gap fault. A-A’, B-B’- cross sections shown in Garihan (2002).

Figure 2. Selected features of Standingstone Mountain quadrangle, NC-SC, with index to quadrangles. BF-Bridal Veil Falls, DSF- Dupont State Forest, CG-Camp Greenville, HF-High Falls, HQ-Holmes Educational Forest Headquarters, JGSP-Jones Gap State Park, MV-Mulligans View, SC-Symmes Chapel, TF-Triple Falls.

Sheet II: Chauga River Formation Ductile deformed muscovite-biotite-feldspar-quartz gneiss and schist of Sheet II underlies a narrow, arcuate zone (0.1-0.8 km wide) striking N55 ̊-75 ̊E. Sheet II is bound on the north edge by the Eastatoee thrust (present at the Dismal Creek stop) and on the south by an unnamed Paleozoic thrust that formed after the Eastatoee fault (cross section, Figure 3). It is conjectured that the unnamed Paleozoic thrust may sole into/merge with the deeper Eastatoee fault at depth. Chauga River Formation rocks form a prominent resistant ridge (200-500 feet relief) which we will see from the Pinnacle Peak overlook (Figure 4). Impressive waterfalls are produced on Chauga River rocks along north-flowing tributaries of west-flowing Crab Creek (Figure 2).

SV SII

SI SIII SIV

Figure 3. Cross section across part of Standingstone Mountain quadrangle, coinciding with the northwest half of the A-A’ cross section line shown on Figure 1. Sheets are labeled SI, SII, SIII, SIV, and SV. Rock units: Henderson Gneiss- forest green, Chauga River Formation- red, Table Rock gneiss- pink, Six Mile thrust sheet rocks- light green. Eastatoee fault separates SI and SII. Paleozoic thrust (post-Eastatoee fault age) separates SII and SIII. Slicking Gap normal fault separates SIII and SIV. Seneca fault separates SIV and SV. Cross section modified from Garihan and Ranson, 2007.

The Chauga River Formation is a uniformly hard, dark, fine-crystalline, poorly to moderately layered muscovite-biotite-feldspar-quartz gneiss. Its variable texture suggests an original metasiltstone protolith; it is locally ‘pebbly’ in appearance in coarser layers. At the Dismal Creek exposures, thin light gray, siltier layers outline isoclinal folds with axial planar schistosity. Locally, shape-modified K-feldspar porphyroclasts (generally < 0.5-1 cm in long dimension, parallel to foliation) are rounded or strongly tapered by ductile deformation. Shear sense indicators are consistent with west- or northwest-directed transport. Coarser muscovite ductile fish (‘buttons’) with finer biotite inclusions are visible on schistosity surfaces, particularly at exposures along NC 1257 at Shoal Creek (Figure 2, which we will not visit).

Figure 4. View to the northwest from Pinnacle Peak. Slopes on left side underlain by Table Rock gneiss. Chauga River Formation ridge is indicated by arrows. Valleys on either side of the ridge are underlain by Henderson Gneiss.

Sheet III: Henderson Gneiss

Henderson Gneiss of Sheet III underlies a zone 0.7-3 km wide (Figure 1). The lithologies are the same as the Henderson Gneiss of thrust sheet I. Foliation attitudes within Sheet III (N32 ̊E, 13 ̊SE; n=60) are essentially the same as foliation attitudes within Sheet I (N37 ̊E, 19 ̊SE; n=34). Impressive, well-jointed exposures of Henderson Gneiss occur within Dupont State Forest at Triple Falls (which we will visit) and High Falls along the Little River (Figure 2, labeled TF and HF). The foliation attitudes in Henderson Gneiss are truncated by a fault at the top of Sheet III. The nature of this contact between Henderson Gneiss (below) and Table Rock gneiss (above) is equivocal because the southeast-dipping contact is not exposed. Nonetheless, mutual intrusive relationships are absent. The contact is interpreted to be the northeastern continuation of the Slicking Gap normal fault found

5 in Table Rock quadrangle (Garihan and Ranson, 2003) because older orthogneisses occur in the footwall and younger orthogneisses in the hanging wall. This normal fault is shown with the bar and ball symbol on Figure 1. In a few places the Slicking Gap normal fault is offset by small faults of north-northwest strike (local offsets of 0.5-1 km).

Sheet IV: Table Rock gneiss

Sheet IV (Figure 2) contains resistant (quartzose) Table Rock Plutonic Suite biotite gneiss and, particularly in southern SM, lesser biotite-feldspar augen gneiss (labeled TRag on Figure 1). The latter augen gneiss, which is not Henderson Gneiss, is middle Ordovician, U-Pb dated at 450 Ma (Ranson and others, 1999). Locally interlayered amphibolite and minor schist are present in Sheet IV. Metagabbro and ultramafic schists, found commonly in adjacent Table Rock quadrangle to the southwest, are notably absent along strike in SM.

At the overlook ridge (Blue Moon at Pinnacle Peak community, 'The Pinnacle' on Figure 5) we will see rounded, exfoliated exposures and landscape blocks of typical Table Rock gneiss, some with chevron and isoclinal folds. From the overlook to the northwest we can see the narrow resistant ridge of Sheet II underlain by Chauga River Formation rocks (Figure 4).

Sheet V (Six Mile) Poor Mountain and Tallulah Falls Formations

Rocks of the Poor Mountain and Tallulah Falls formations lie at the higher elevations of SM (2200-3600 feet). They comprise discontinuous klippen of the Six Mile thrust sheet, with the Seneca fault at its base. We will take a short walking traverse across the margin of a klippe of Six Mile rocks, tracing the Seneca fault (Figure 5). The irregular regional trace of the Seneca fault in central and south SM is due to a combination of factors: 1) a shallow regional southeastward dip; 2) the rugged relief in the region, prompted by Cenozoic uplift and deep erosion; and 3) the complex geometry of the fault surface. The latter is produced by several phases of folding younger than and hence deforming the Seneca fault surface.

Post-Seneca, southwest-divergent, overturned antiformal folding of the Seneca surface has produced several windows exposing footwall Table Rock gneiss at structural culmination positions. That is, at these locations the Seneca thrust has been arched up and subsequently eroded through, exposing underlying footwall rocks at the surface. In Figure 1, the culminations are shown as dotted ovals and circles surrounded by hanging wall Six Mile rocks. On the geologic map of Figure 5, these structural windows are shown as Table Tock gneiss exposure areas surrounded by Six Mile rocks. The fault between them is the Seneca fault (sawtooth line).

Figure 5. Portion of eastern Standingstone Mountain geologic map showing structural windows through the Six Mile thrust Sheet V. Table Tock gneiss- pink, labeled TRg. Six Mile rocks- green, labeled PM(s). Circled area- Pinnacle Mountain Road traverse across klippe margin. Seneca fault- sawtooth line. Large red circle denotes area of traverse across margin of klippe. Geology from Garihan and Ranson, 2007.

7 Rocks of the Poor Mountain Formation in the Six Mile sheet include abundant amphibolite, garnet- mica schist, biotite-muscovite gneiss, and metaquartzite. Rocks of the Tallulah Falls Formation include muscovite-biotite-sillimanite gneiss, muscovite-biotite-sillimanite schist, biotite- porphyroblastic feldspar gneiss, biotite gneiss, minor amphibolite, and calc-silicate gneiss. The units are migmatitic; commonly they contain quartz-feldspar (granitoid) layers and lenses, which serve to substantially thicken the metamorphic sequence.

Summary

The emphasis of this field trip is: 1) to view the metamorphic rock types within each sheet; and 2) to describe the nature of the faults that separate them. Henderson Gneiss underlies Sheets I and III. The ductile Eastatoee fault lies at the base of Sheet II, and the ductile Seneca fault lies at the base of Sheet V. The Slicking Gap normal fault separates Henderson Gneiss of Sheet III and Table Rock gneiss of Sheet IV. The Figure 3 cross section, northwest (left) to southeast (right), shows the vertical structural stacking of the five fault-bound crystalline sheets in Standingstone Mountain quadrangle. Garihan and Clendenin (2007) consider the Henderson Gneiss exposures to be part of the Jocassee thrust sheet.

Hanging wall and footwall units of the Eastatoee fault are seen to be duplicated by later faulting in our traverse along the CCC Camp Road at Dismal Creek. In addition, we make a walking traverse along Pinnacle Mountain Road (NC 1114) across the hanging wall and footwall units of the Seneca fault south of Pinnacle Peak (circled location on Figure 5). Here Six Mile fine-crystalline mica gneiss, amphibolite, and quartzite in the hanging wall overlie a sandy-weathering, light colored Table Rock gneiss footwall. These roadcut exposures are unusual in that the fault contact can be easily traced laterally.

No other western Inner Piedmont area has the complexity of the Standingstone Mountain region, with its stack of five distinct, fault-bound sheets present within just one quadrangle.

8 References

Cattanach, Bart L., and Bozdog, G. Nicholas, 2011, Bedrock Geologic Map of the Brevard Quadrangle, Transylvania County, North Carolina: North Carolina Geologic Survey, Open File Report 2011-01, 1:24,000 scale

Garihan, John M., 2001, Observations of the Seneca fault and their implications for thrust sheet emplacement in the Inner Piedmont of the Carolinas: in Garihan, J.M. and Ranson, W.A., eds., Geology of the Inner Piedmont in the Caesars Head and Table Rock State Parks area, northwestern South Carolina, South Carolina Geology, v. 43, p. 1-13.

Garihan, John M., 2002, Geology of Standingstone Mountain quadrangle, western Inner Piedmont, North and South Carolina: in Hatcher, Jr., R. D, and Bream, B. R., eds., Inner Piedmont Geology in the South Mountains-Blue Ridge Foothills and the southwestern Brushy Mountains, central-western North Carolina, North Carolina Geological Survey, Carolina Geological Society Annual Field Trip Guidebook, p. 19-32.

Garihan, John M., 2005, Geologic Map of the Cleveland 7.5-minute quadrangle, Greenville and Pickens Counties, South Carolina: South Carolina Department of Natural Resources, Geological Survey, Geological Quadrangle Map 33, 1:24,000 scale

Garihan, J. M. and W. A. Ranson, 2003, Geologic map of the Table Rock 7.5-minute quadrangle, Greenville and Pickens counties, South Carolina: South Carolina Department of Natural Resources, Geological Survey, Geologic Quadrangle Map GQM 9, 1:24,000 scale.

Garihan, John M., and Ranson, W. A., 2007, Geologic map of the Standingstone Mountain 7.5- minute Quadrangle, Greenville County, South Carolina and Transylvania and Hendersonville Counties, North Carolina: South Carolina Department of Natural Resources, Geological Survey, Geological Quadrangle Map 35, 1:24,000 scale.

Garihan, J.M., and Clendenin, C. W., 2007, Recognition of the Eastatoee fault in northwest South Carolina and adjacent North Carolina, South Carolina Geology, v. 45, p. 1-8.

Hatcher, R. D., Jr., 2001, Rheological partitioning during multiple reactivation of the Palaeozoic Brevard fault zone, southern Appalachians, in Holdsworth, R. E., Strachan, R. A., Magloughlin, J. F., and Knipe, R. J., eds., The nature and tectonic significance of fault zone weakening: Geological Society of London, Special Publication 186, p. 257-271.

Ranson, W. A., Williams, I. S. and Garihan, J.M., 1999, Shrimp zircon U-Pb ages of granitoids from the Inner Piedmont of South Carolina: Evidence for Ordovician magmatism involving mid to late Proterozoic crust: Geol. Soc. America Abstracts with Programs, v. 31, n. 7, p. A-167.

9 Field Trip Stops (all Lat/Longs listed are in NAD83/WGS84)

Figure 6. Generalized geologic map with field trip stops modified from Garihan and Ranson 2003, Garihan 2005, Garihan and Ranson 2007, and Cattanach and Bozdog 2011. See legend on next page.

Stop 1: Caesars Head State Park Visitor Center, SC: Devils Kitchen Trail (35.1058, -82.6265)

A short walk along the escarpment from the parking lot brings you to an impressive overlook that allows a view of the Piedmont and the southwest extension of the Blue Ridge. Fractures in the Table Rock gneiss are enlarged and conspicuous due to ridge extension that will eventually lead to the collapse of this overlook. The fracture face of the block upon which Jack Garihan is standing (Figure 7) is oriented N30oW and terminates against the E-W trending extension joint. The imposed extensional forces on the two dominant facture sets produces an interesting set of features called the Devils Kitchen (Figure 8) that are located about 50 feet to the left of where Jack is standing in Figure 7.

Figure 7. Stop 1. Overlook at Caesars Head State Park, SC with fracture spacing enlarged by ridge extension.

Figure 8. N30oW trending facture enlarged by ridge extension, Devils Kitchen Trail, Caesars Head State Park, SC

12 Stop 2: Triple Falls via the Hooker Falls Access Parking Lot, Dupont State Forest, NC (35.1995, -82.6169)

From the parking lot, hike upriver on the trail, cross the bridge, and continue until till you reach the intersection on the trail between the lower and middle cascades of the Triple Falls. At the trail intersection, wooden stairs descend on the left to a large pavement exposure of the Henderson Gneiss at the base of the middle cascade (Figure 9). The water descends on cascade faces defined by fractures that trend N50oE and are cut by another set of fractures that trend N50oW (Figure 10). The Henderson Gneiss at this location is mylonitic and asymmetric recrystallized tails indicate northwestward movement (Figure 11).

Figure 9. Stop 2. View of the middle cascade of the Triple Falls at Stop 2 with large pavement exposures of Henderson Gneiss, Dupont State Forest, NC. View to the southeast.

13 S

Figure 10. Compass lined up with N50oW trending fracture that cuts across N50oE trending fractures upon which the falls are formed, Dupont State Forest, NC

Figure 11. Asymmetric quartz-feldspar tails on microcline indicate top to northwest (right) ductile shearing, Dupont State Forest, NC

14 Stop 3: Pinnacle Mountain Overlook, Blue Moon at Pinnacle Peak, NC (35.2306, -82.5447)

Warning: This stop is located on private property and permission MUST be obtained before accessing this location. Please respect the rights of landowners and leave the land in better condition than you found it. We are their guests.

The top of the ridge is underlain by Table Rock gneiss (TRg) and the view from the covered pavilion is to the north-northwest. In the valley bottom, the Eastatoee thrust (Figure 3) brings up a northeast-trending, low ridge of more resistant Chauga River Formation (CRfm) (Figure 12). Between the top of the ridge (TRg) and the bottom of the valley (Hgn) the Slicking Gap normal fault separates the downthrown (but topographically higher) Table Rock gneiss from the upthrown (but topographically lower) Henderson Gneiss (Figure 13).

N Hgn

CRfm

Hgn

TRg

Figure 12. Stop 3. Table Rock gneiss (Trg) exposed at top of Pinnacle Mountain near the covered pavilion at Blue Moon at Pinnacle Mountain, NC. Low ridge in valley floor is Chauga River Formation (CRfm). The Eastatoee fault places CRfm over Henderson Gneiss (Hgn); it dips toward the observer about 28o southwest. View to the northwest.

15 Hgn

Eastatoee fault CRfm

Hgn

Up Slicking Gap Down normal fault Trg

Figure 13. Geologic map of pertinent features observed from Pinnacle Mountain overlook. TRg = Table Rock gneiss, Hgn = Henderson Gneiss, Crfm = Chauga River Formation. Geology from Garihan and Ranson, 2007.

Stops 4-11: Pinnacle Mountain Road, NC: Post-lunch execise.

These stops are part of a walking traverse along Pinnacle Mountain Road where the Seneca fault contact can be traced laterally (Figure 14).

16 Trg

Figure 14. Locations of Stops 4-11 along Pinnacle Mountain Road (denoted by double dashes). TRg = Table Rock gneiss, PM = Poor Mountain Formation. Geology from Garihan and Ranson, 2007.

17 Stop 4: Pinnacle Mountain Road, NC (35.2265, -82.5410)

At this stop, Poor Mountain Formation is thrust over Table Rock gneiss along the Seneca fault. The leucocratic Table Rock gneiss produces light colored soils and weathers faster than the Poor Mountain Formation (Figure 15).

Trg

Figure 15. Stop 4. Resistant slab of Poor Mountain Formation (PM) in the hanging wall, with Table Rock gneiss (TRg) in the footwall. Thrust movement toward observer.

Stop 5: Pinnacle Mountain Road, NC (35.2261, -82.5414)

This outcrop exposes thin (~1 mm) compositional layers in the Table Rock gneiss following the foliation. The shearing and grain size reduction are related to the Table Rock gneiss in close proximity to the Seneca Fault. (Figure 16)

Figure 16. Stop 5. Thin (~1 mm) compositional layers in the Table Rock gneiss.

Stop 6: Pinnacle Mountain Road, NC (35.2260, -82.5414)

The color change in the soil horizon from dark to light indicates a transition from Poor Mountain Formation to Table Rock gneiss. The Seneca Fault is covered but easily located (Figure 17). Soils are a key in geologic mapping!

Seneca Fault

TRg

Figure 17. Stop 6. Poor Mountain Formation (PM) in the hanging wall, with Table Rock gneiss (TRg) in the footwall.

Stop 7: Pinnacle Mountain Road, NC (35.2257, -82.5416)

An exposure of Poor Mountain amphibolite strikes N60oE and dips 16oSE in Figure 18.

Figure 18. Stop 7. Poor Mountain Formation amphibolite in the hanging wall.

Stop 8: Pinnacle Mountain Road, NC (35.2251, -82.5418)

Large outcrop of Tallulah Falls gneiss with purple paint spot (Figure 19). This outcrop is in the hanging wall above the Seneca Fault. The gneiss at this location is a fine-crystalline, medium gray biotite gneiss with tight-isoclinal folds. The foliation is axial planar to the folds. The Seneca fault is below your feet here. Be careful where you step!

Figure 19. Stop 8. Tallulah Falls gneiss with folds. Can you see them?

Stop 9: Pinnacle Mountain Road, NC (35.2240, -82.5424)

Dark gray, quartzose garnet Tallulah Falls gneiss (Figure 21). Metamorphosed zones within this paragneiss may reflect the variability of this formation due to its sedimentary origin. Biotite in this gneiss is more abundant than in the Table Rock gneiss.

Figure 20. Stop 9. Biotite gneiss of the Tallulah Falls Formation. Dark zones are aligned fine- crystalline biotite outlining small folds.

21 Stop 10.: Pinnacle Mountain Road, NC (35.2234, -82.5436)

At this large pull-off, thinly layered, fine-crystalline amphibolite of the Poor Mountain Formation litters the slope in broken pieces (Figure 21). You are still in the hanging wall!

Figure 21. Stop 10. Thinly layered pieces of Poor Mountain Formation in roadcut.

Stop 11: Pinnacle Mountain Road, NC (35.2239, -82.5443)

This is the final stop of the Pinnacle Mountain road traverse. While there are no outcrops, the thinly layered, leucocratic float indicates Table Rock gneiss here. Hence the Seneca fault was crossed over your head between this location and the pull-off at Stop 10.

Stops 12-15: Dismal Creek, Old CCC Road, NC

Stops 12-15 are a downhill walking traverse down-section across the Chauga River Formation. Below it is a fault-bounded sliver of Henderson Gneiss (Figure 22). A schematic cross-section along the road is shown in Figure 23.

22 A

Figure 22. Locations of stops 12-15 along Old CCC Road. Geology from Garihan and Ranson, 2007. A-B is position of schematic cross section of Figure 23.

Figure 23. Schematic cross-section of fault relationships along Dismal Creek traverse: Stops 12, 13, 14, and 15. E=Eastatoee fault, P=Paleozoic thrust.

Stop 12: Dismal Creek, Old CCC Road, NC (35.2370, -82.5562)

The Chauga River Formation is separated from the Henderson Gneiss by the Eastatoee fault. The Chauga River Formation is in the hanging wall, and the Henderson Gneiss is in the footwall. At the outcrop on the northeast side of the Old CCC Road, the Chauga River Formation is micaceous with visible quartz and feldspar crystals up to 1 cm in length (Figure 24). The Chauga River Formation varies from micaceous to quartzose which reflects differences in its sedimentary protolith (shaly to sandy). Thin sections made from the block shown in Figure 24 are presented in Figures 25, 26, 27, and 28. In Figures 25 and 26, the thin section allows visualization of the micaceous schistosity wrapping around the coarser quartz and feldspar grains. The plagioclase displays lamellar twinning under cross-polarized light. In Figures 27 and 28, the thin section allows a closer examination of the relative sizes of the muscovite and biotite. The muscovite crystals are, on average, about 3-4 times longer than the biotite crystals. A few muscovite crystals are up to 10 times longer than the biotite crystals (Figure 25) and are draped almost entirely around the largest quartz and feldspar crystals, which are up to 1 cm in length. The micas display shear textures.

Figure 24. Float block of Chauga River Formation at Stop 12.Dark, wavy, micaceous schistosity is horizontal. White areas are quartz-plagioclase aggregates.

25 Qtz Ms

Pl Bt

Pl Qtz

1 mm

Figure 25. Photomicrograph of the Chauga River Formation viewed under cross-polarized light at 3.2x. Qtz = quartz, Ms = muscovite, Pl=plagioclase, Bt= biotite.

Qtz Ms

Pl Bt

Qtz Pl 1 mm

Figure 26. Photomicrograph of the Chauga River Formation viewed under plane-polarized light at 3.2x. Qtz = quartz, Ms = muscovite, Pl=plagioclase, Bt= biotite. Same thin section as in Figure 25.

26 Qtz Bt

Ms Bt

Qtz

Bt 0.3 mm Qtz

Figure 27. Photomicrograph of the Chauga River Formation viewed under cross-polarized light at 10x. Qtz = quartz, Ms = muscovite, Bt= biotite.

Qtz Bt

Bt Ms Bt

Qtz

0.3 mm Qtz Bt

Figure 28. Photomicrograph of the Chauga River Formation viewed under plane-polarized light at 10x. Qtz = quartz, Ms = muscovite, Bt= biotite. Same thin section as in Figure 27.

27 Stop 13: Dismal Creek, Old CCC Road, NC (35.2380, -82.5570)

An imbricate thrust fault as shown in Figure 23 has brought up a sliver of Henderson Gneiss on both sides of the Chauga River Formation. Approximately 60 feet of Henderson Gneiss is exposed along the road (Figure 29).

Lichen

Figure 29. Henderson Gneiss exposure at road level at Stop 13. Note the white cm-long feldspar augen ("eyes") are modified in shape by shearing mylonization. The large white patch is lichen coating the flat joint surface.

28 Stop 14: Dismal Creek, Old CCC Road, NC (35.2381, -82.5573)

Moving down the road from Stop 13, the imbricate thrust fault is passed and Chauga River Formation is exposed. The Henderson Gneiss produced light colored soils when the leaf litter is removed compared to darker soils of the Chauga River Formation.

Hgn

CRfm

Figure 26. Stop 14. Contact between Henderson Gneiss and Chauga River Formation. Red circle indicates light colored soils produced by weathering of Henderson Gneiss. Yellow dashed line is a later Paleozoic fault.

29 Stop 15: Dismal Creek, Old CCC Road, NC (35.2381, -82.5577)

Figure 27 shows the lower covered Henderson Gneiss (foreground) - Chauga River Formation contact. Cross section of contact shown in Figure 23.

CRfm

Hgn

Figure 27. Stop 15. Geologist sits on Eastatoee fault position. Above the fault is the Chauga River Formation and the Henderson Gneiss is below (foreground). View is to the northeast.

Stop 16: OPTIONAL, Caesars Head State Park, SC

If time permits we will look at a relationship that, regionally speaking, is upside-down. We will take a short walk down the trail from Rt. 276 and Cliff Ridge. This interesting exposure shows smooth, exfoliated Table Rock gneiss sitting on top of amphibolite layers. The amphibolite is extensively covered by moss, lichen, and grey coatings. The amphibolite has been intruded along its compositional layers – and along a local, internal fault (oriented N20E°, 32°SE) – by sills of granitoid-pegmatite. One prominent dike of granitoid-pegmatite in amphibolite (see Figure 28) is folded into a Z-shape.

30 The contact between the gneiss above and the amphibolite below is abrupt, at the overhang on the upper right side of the figure. At least two explanations for the relationships shown in the exposure are possible. First, the amphibolite is another example of a metamorphosed mafic intrusion, common within the main body of Table Rock orthogneisses (TRg) of the Walhalla thrust sheet. Alternately, the sharp contact is a thrust placing this gneiss over Poor Mountain Formation (PM) amphibolite of the Six Mile thrust sheet. Regional mapping indicates that this is a thrust fault, one of the Caesars Head fault system (Figure 29). Along it, rocks of the Walhalla thrust sheet have been moved to the south or southwest across rocks of the Six Mile thrust sheet, contrary to regional relations.

TRg

Figure 28. Optional stop16, near Cliff Ridge. Rounded Table Rock gneiss lies above compositionally layered amphibolite. Scale in centimeters sits on folded granitoid-pegmatite dike.

Figure 29. Caesars Head thrust fault system (open-tooth thrust symbol), marked by blue arrows. Optional stop 16 location is circled.