Neoproterozoic to Mesozoic Petrologic and Ductile-Brittle Structural

The Geological Society of America Field Guide 29 2012

Neoproterozoic to Mesozoic petrologic and ductile-brittle structural relationships along the Alleghanian Nutbush Creek fault zone and Deep River Triassic basin in North Carolina

David E. Blake Department of Geography and Geology, University of North Carolina Wilmington, 601 S. College Road, Wilmington, North Carolina 28403-5944, USA

Edward F. Stoddard North Carolina Geological Survey, 1620 Mail Service Center, Raleigh, North Carolina 27699-1620, USA, and Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina 27695-8208, USA

Philip J. Bradley North Carolina Geological Survey, 1620 Mail Service Center, Raleigh, North Carolina 27699-1620, USA

Timothy W. Clark Wake Technical Community College, 9101 Fayetteville Road, Raleigh, North Carolina 27603, USA

ABSTRACT

The focus of this ﬁ eld trip is the complex lithologic, metamorphic and structural transition between high-grade infrastructural and low-grade suprastructural terranes that deﬁ ne the accreted peri-Gondwanan Neoproterozoic-Cambrian Carolina Zone, an island-arc superterrane in the north-central Piedmont of North Carolina. This transition is now exposed across a metamorphic suite of amphibolite facies layered gneiss plus kyanite-sillimanite zone pelitic schist, and another metamorphic suite of greenschist facies mylonitic and phyllonitic metagranitoids and their undeformed equivalents. A variety of mineral assemblages, fabric elements, and structures within the transition zone may be linked into a progressive sequence recording (1) the transpressional buildup of an Alleghanian collision zone between Laurentia, the Carolina Zone, and Gondwana during Pangean continental amalgamation, and (2) its extensional collapse during the Permo-Triassic through Jurassic rifting and breakup of Pangea. We will observe the effects of Alleghanian ductile strain superposed on this infrastructural-suprastructural terrane transition, including the interplay between

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Blake, D.E., Stoddard, E.F., Bradley, P.J., and Clark, T.W., 2012, Neoproterozoic to Mesozoic petrologic and ductile-brittle structural relationships along the Alleghanian Nutbush Creek fault zone and Deep River Triassic basin in North Carolina, in Eppes, M.C., and Bartholomew, M.J., eds., From the Blue Ridge to the Coastal Plain: Field Excursions in the Southeastern United States: Geological Society of America Field Guide 29, p. 219–261, doi:10.1130/2012.0029(07). For permission to copy, contact [email protected]. © 2012 The Geological Society of America. All rights reserved.

219 220 Blake et al.

dextral transpression and the generation of syn- to post-kinematic granitic plutons. Metamorphosed volcanogenic and syn-kinematic granitoid rocks record the effects of ductile dextral-slip deformation associated with at least four major fault zones. These fault zones are combined as the Nutbush Creek–Lake Gordon fault system, an integral member of the Eastern Piedmont fault system. Finally, the trip highlights the ductile-brittle effects of Late Permian to Triassic normal-slip faulting, uplift and rift sedimentation in the northern Durham sub-basin of the Triassic Deep River rift basin, as well as crosscutting Jurassic intrusive rocks.

INTRODUCTION and structures in north-central North Carolina. The region lying between the capital city of Raleigh and Kerr Lake Recreation The starting point for much of the modern geologic map- Area located along the North Carolina–Virginia state line has ping in the transition from the eastern to central Piedmont been the primary focus of these mapping efforts. Noted for its in north-central North Carolina involves the work of Parker 800 miles of shoreline (www.ncparks.gov), Kerr Lake State Rec- (1968, 1978, 1979). He showed that the region is composed reation Area, together with major southeast-fl owing tributaries to of a variety of rock types and metamorphic assemblages that the Tar River and Falls Lake–Neuse River drainage basins to its are overprinted by multiple ductile and brittle deformations. south provide abundant erosional exposures. These will be used Parker’s mapping served as the basis for lithologic contacts on this two-day fi eld trip to examine rocks representing mid-to- in north-central North Carolina on the most recent version of upper-crustal levels in cross-strike and along-strike traverses and the state geologic map (North Carolina Geological Survey, the geologic transition between the eastern and central Piedmont. 1985). It also served as the foundation for a major regional Outcrops in this transition expose varying scales of windows into geologic overview by Farrar (1985a, 1985b), who presented a Neoproterozoic to Jurassic crystalline and sedimentary rocks. synopsis of the stratigraphy, structure, and metamorphic his- They also provide a view of the low- to medium-grade metamor- tory of the eastern Piedmont based on his own reconnaissance- phism and ductile-brittle fault zone relationships and structures level geologic mapping and sampling. In continuity with the associated with the transition from Paleozoic transpressional regional studies by Farrar, Harris and Glover (1988) provide a orogenesis to Mesozoic extensional rifting of eastern North synopsis of the stratigraphic, structural, and metamorphic devel- America. These events document the fi nal pulses of Laurentian- opment of the northeastern portion of the central Piedmont based Gondwanan amalgamation and subsequent breakup of the Pan- upon regional fi eld studies and stratigraphic correlations. gean supercontinent. Additional geologic mapping across the eastern-to-central The study area is separated into amphibolite (infrastructural) Piedmont transition in the north-central North Carolina includes and greenschist facies (suprastructural) terranes that lie within a fi ve-county NCGS reconnaissance map by McDaniel (1980), the orogen-scale, Neoproterozoic-Cambrian Carolina Zone, a the USGS 1:100K South Boston sheet geologic map by Hor- peri-Gondwanan island-arc superterrane (Fig. 1). Specifi cally, ton et al. (1993a; 2001), an east-west strip of four USGS 1:24K the fi eld trip will focus upon the complex petrologic transition geologic maps along the North Carolina–Virginia state line by from deeper infrastructural to shallower suprastructural terranes. Sacks (1996a, 1996b, 1996c, 1996d), as well as the fi eldwork of This transition is now exposed across a suite of amphibolite facies Cook (1963), Carpenter (1970), Hadley (1973, 1974), McCon- layered gneiss and kyanite-sillimanite zone pelitic schist, and nell (1974), McConnell and Glover (1982), Hoffman and Gal- greenschist facies mylonitic and phyllonitic metagranitoids and lagher (1989), and Gottfried et al. (1991). Several studies pro- their undeformed equivalents. We will observe the superposed viding additional geologic mapping include those focused on the effects of Pennsylvanian–Early Permian, Alleghanian orogeny Hamme tungsten deposit in the central Piedmont (Parker, 1963; ductile-brittle strain on this terrane transition, including the inter- Casadevall and Rye, 1980; Foose et al., 1980; LeHuray, 1989), play between dextral-slip transpression and generation of syn- and on the late Paleozoic, Alleghanian Nutbush Creek fault zone to post-kinematic granitic plutons. Finally, the trip highlights in the eastern Piedmont (Casadevall, 1977; Hatcher et al., 1977; ductile-brittle effects of Permo-Triassic normal-slip faulting, and Bobyarchick, 1981; Druhan, 1983; Druhan et al., 1994) then uplift and rift sedimentation linked to the Durham sub-basin Since the completion of the regional mapping by Farrar and of the Triassic Deep River basin, as well as crosscutting Jurassic then by Harris and Glover, the central and eastern Piedmont has diabase intrusive bodies. been the subject of 27 years of detailed geologic mapping of all From north to south, as well as east to west, fi eld trip stops or parts of over 50 1:24K quadrangles in the Raleigh and Hender- are located within the John H. Kerr Dam, Middleburg, Hender- son 1:100K sheets, largely from the efforts of the North Carolina son, Oxford, Wilton, and Lake Michie 1:24K Quadrangles (Figs. Geological Survey (NCGS). Detailed NCGS geological map- 2, 3, and 4). This fi eld trip honors the 75th anniversary of the ping under the USGS-administered STATEMAP and EDMAP establishment of the Carolina Geological Society and its contri- programs has added clarity to our understanding of rock types bution to our understanding of southern Appalachian geology. Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 221

Figure 1. Tectonostratigraphic element map of suprastructural and infrastructural terranes within the Carolina Zone of the southern Appalachian orogen. Suprastructral elements include the Milledgeville (MT), Augusta (AT), Roanoke Rapids (RR), Spring Hope (SH), Carolina (CT), and Easternmost Carolina (ECT) terranes. Infrastruc- tural elements include the Uchee (UT), Savannah River (SR), Dreher Shoals (DS), Falls Lake (FLT), Triplet (TT), Warren (WT), Raleigh (RT), Crabtree (CRT), and Charlotte (CHT) terranes. VA—Virginia; TN—Tennessee; NC— North Carolina; AL—Alabama; GA— Georgia; SC—South Carolina. Modiﬁ ed from Hibbard and Samson (1995) and Hibbard et al. (2002).

Figure 2. Regional geologic setting of the northeastern Carolina Zone showing tectonostratigraphic terranes, Dur- ham sub-basin (Dsb) of the Deep River Mesozoic rift basin, and major late Pa- leozoic granitoid plutons (Rolesville (R) and Buggs Island (B). Suprastruc- tral elements include: Roanoke Rapids (RRt), Spring Hope (SHt), Carolina (Ct), and easternmost Carolina (ECt) terranes. Infrastructural elements include the Falls Lake (FLt), Triplet (Tt), Warren (Wt), Raleigh (Rt), and Crab- tree (Cbt) terranes. Terrane-bounding ductile dextral-slip fault zones highlighted by name and arrows include, from east to west, Gaston Dam, Hol- lister, Macon, Middle Creek, Lake Gor- don, Neuse River, Falls Lake, Nutbush Creek; ductile-brittle normal-slip fault zones include the Fishing Creek, Jones- boro, and Upper Barton Creek. 222 Blake et al.

Figure 3. Map showing ﬁ eld trip stops for Day 1 with preliminary bedrock geologic map of the Henderson, southeast portion of the Townsville, Middleburg, and North Carolina portion of the John H. Kerr Dam 1:24K Quadrangles. Select map units identiﬁ ed. Map is compiled from NCGS STATEMAP mapping data. Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 223

Figure 4. Map showing ﬁ eld trip stops for Day 2 with preliminary bedrock geologic map of the Oxford, Wilton, Stem, and portions of the Lake Michie, Grissom, Creedmoor, and NE Durham 1:24K Quadrangles. Select map units identi- ﬁ ed. Map is compiled from NCGS STATEMAP mapping data. 224 Blake et al.

Numerous CGS fi eld trips and discussions in the eastern-to- Most faults show dextral-slip displacements, although the central Piedmont transition of both North Carolina and South Macon and Hyco fault zones in North Carolina and Virginia are Carolina have helped guide the geologic mapping progression partitioned as ductile thrusts (Sacks, 1999; Hibbard et al., 1998). and conceptual interpretations presented here. As a group, these Alleghanian faults affect the (1) Mesoprotero- zoic to Cambrian eastern margin of Laurentia, (2) Neoprotero- GEOLOGIC SETTING zoic to Cambrian metasedimentary and metavolcanic rocks of the Piedmont Zone, and (3) Neoproterozoic to Cambrian island-arc Lithotectonic Elements of North-Central North Carolina rocks of the Carolina Zone (Fig. 1; Gates et al., 1988; Costain et al., 1989; Blake et al., 2001). In north-central North Carolina, the eastern and central The area of the fi eld trip also lies along the western fl ank of Piedmont Physiographic Province of the southern Appalachian the south-plunging Wake-Warren anticlinorium (Fig. 2; Parker, orogen exposes a diverse array of meta-igneous, metasedimen- 1979; Farrar, 1985a; Stoddard et al., 1991; Horton et al., 1994), tary, plutonic, and sedimentary rocks. These rocks and numerous an arch of foliation across a region generally called the Raleigh overprinting ductile and brittle faults collectively range in age metamorphic belt. It exposes rocks displaying Alleghanian from the Neoproterozoic to early Mesozoic. A system of north- amphibolite facies metamorphism in its core terranes, and grades northeast–trending fault zones known as the Eastern Piedmont outward to greenschist facies to the east and west in the Spring fault system (Hatcher et al., 1977; Bobyarchick, 1981; Stoddard Hope and Carolina terranes, respectively. The Pennsylvanian et al., 1991) divides pre-Mesozoic rocks into numerous terranes Rolesville batholith, a large composite granitoid pluton, intruded within the larger tectonic realm known as the Carolina Zone mainly within the hinge zone and western fl ank of the Wake- (Hibbard and Samson, 1995; Hibbard et al., 2002). Warren anticlinorium. The weakly to unfoliated nature of large The origin of each terrane appears to be a common Neo- portions of the batholith locally supports a late- to post-kinematic proterozoic to early Paleozoic, peri-Gondwanan island-arc set- emplacement history during the Alleghanian orogeny. Other ting exotic to Laurentia. From the eastern Piedmont and west- portions, especially those injected adjacent to or within dextral ward across to the central Piedmont, these tectonostratigraphic ductile shear zones, display strong tectonic overprint, including a terranes include the Roanoke Rapids, Triplet, and Spring Hope progression of proto-mylonitic to mylonitic fabric elements. terranes, the herein named Warren terrane, and then the Raleigh, On the western fl ank of the Wake-Warren anticlinorium, Crabtree, Falls Lake, and Carolina terranes (Fig. 1; Blake et al., individual fault zone strands anastomose around terrane ele- 2001; Clark et al., 2004; Hibbard et al., 2002; Sacks, 1999). The ments to form a 1–10-km-wide dextral-slip fault system that is deeper crustal and infrastructural Raleigh and Warren terranes, one of the principal structures of the northeast-trending East- and the shallower and suprastructural Carolina terrane are three ern Piedmont fault system (Hatcher et al., 1977; Bobyarchick, of the most regionally extensive portions of the Carolina Zone 1981). This structure is herein termed the Nutbush Creek–Lake across the eastern-to-central Piedmont transition. Their rocks are Gordon fault system. It has been traced for over 200 km from the primary focus of the fi rst fi eld trip day. the North Carolina–Virginia state line into south-central North These terranes are interpreted to record the (1) magmatic Carolina (Figs. 2 and 3; Farrar, 1985a, 1985b; Stoddard et al., and volcaniclastic evolution of this composite, peri- Gondwanan 1991; Druhan et al., 1994; Blake et al., 2001). Topographic and island-arc superterrane, (2) intra-arc tectonism during the ca. lithologic lineaments, dextral L>S tectonite fabric, and rock 560 Ma Virgilina deformation (Glover and Sinha, 1973; Harris types facilitate mapping each fault zone strand and help to dif- and Glover, 1988; Wortman et al., 2000), and (3) accretion of ferentiate individual lithotectonic terranes. Linear aeromagnetic the Carolina Zone to eastern Laurentia during the middle Paleo- anomalies (Casadevall, 1977) also mark the positions of fault zoic Taconic/Cherokee orogeny (Hibbard et al., 2010, 2012). zones. They have been used to extend the eastern Piedmont fault Tectonothermal metamorphism of the eastern Piedmont culmi- system from the North Carolina Piedmont into Virginia and nated in the late Paleozoic during Laurentian-Gondwanan conti- beneath the Atlantic Coastal Plain into the South Carolina Pied- nental collision and construction of the Pangean supercontinent mont (Secor et al., 1986a, 1986b). (Hatcher et al., 1977; Horton et al., 1994; Blake et al., 2001). As Permo-Triassic ductile-brittle normal-slip faults, Triassic Laurentia merged with Gondwana during the Alleghanian orog- clastic sedimentary rocks that nonconformably overlap crystal- eny, oblique convergence deformed the southern Appalachians line rocks, and Jurassic diabase dikes, common throughout the into a kinematically partitioned, strike-slip and dip-slip conti- Piedmont, and sills within the rift basins, document Mesozoic nental collision zone of foreland and hinterland rocks (Secor et rifting and the Pangean supercontinent breakup (Olsen et al., al., 1986a, 1986b; Hatcher et al., 1989). In the eastern-to-central 1991; Clark et al., 2001, 2011; Hames et al., 2001). The Jones- Piedmont transition, hinterland dextral transpression progres- boro fault and the Fishing Creek fault zone (FCFZ) overprint the sively reactivated antecedent dip-slip structures and produced an western fl ank of the Wake-Warren anticlinorium (Figs. 2 and 4). anastomosing network of northeast-trending fault zones from the Together, they defi ne the eastern margin of the Durham sub-basin Virginia Piedmont south into North Carolina (Fig. 2; Gates et al., of the Triassic Deep River rift basin and are the focus of the sec- 1988; Bobyarchick, 1988; Hatcher et al., 1977, 1989). ond day of the fi eld trip (Figs. 4 and 5). The basin, associated Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 225

ductile- brittle faulting, and a variety of mesoscale extensional Infrastructural Terranes structures also overprint and complicate the eastern-to-central Piedmont transition and its underlying terranes (Heller et al., Historically, the Raleigh terrane has been considered to be 1998; Blake et al., 2001). The structural development overprint- the easternmost terrane on the western fl ank of the Wake-Warren ing the eastern-to-central Piedmont transition, as well as the War- anticlinorium. It extends across the hinge zone of this regional ren and Raleigh to Carolina terrane boundary in north-central fold structure, and contains a mixed assemblage of amphibo- North Carolina marks a late Paleozoic to early Mesozoic ductile- lite facies igneous and sedimentary protoliths that experienced to-brittle structural and tectonic transition as well. This transi- kyanite-sillimanite zone tectonothermal metamorphism and mul- tion links a variety of structures and fabric elements, originally tiple granitoid intrusion during the Alleghanian orogeny. thought to be widely separated in time and space, into a progres- The Rolesville batholith has been used to subdivide the sive, and relatively coherent deformational sequence refl ecting Raleigh terrane into two parts across the hinge of the anticlino- the transpressional buildup of an Alleghanian collision zone rium (Fig. 2; Stoddard et al., 1991; Speer, 1994). Southwest between Laurentia, the Carolina Zone, and Gondwana during of the batholith on the western fl ank of the anticlinorium, the Pangean amalgamation and its subsequent extensional collapse terrane contains the Raleigh Gneiss, a lithodeme of heteroge- during Pangean breakup and Wilsonian continental dispersal. neously mixed mafi c to granitoid intrusions, minor schist and the

Fundy Atlantic Coastal Plain CP Newark Supergroup Jurassic Diabase

0 200 400 Chatham Group Undivided EP Deerfield Polymictic Conglomerate Colon Hartford cross - structure Pomperaug Sanford Formation Newark

Gettysburg Cumnock Formation

Culpeper Pekin Formation N

Taylorsville Scottsburg Farmville Richmond Dan River/ Danville

Davie County Deep River 0 20

NC Strike and Dip Normal Fault, Dashed SC of Bedding Where Concealed

Figure 5. Generalized geologic map of the Deep River basin, showing the Durham, Sanford, and Wadesboro sub-basins. The Sanford, Cumnock and Pekin Formations are limited to the Sanford sub-basin. Thin red lines trending north-south to northwest-southeast are Jurassic diabase dikes. CP = Central Piedmont, EP = Eastern Piedmont. Modiﬁ ed from Reinemund (1955), Bain and Harvey (1977), NCGS (1985), Olsen et al. (1991), Hoffman and Gallagher (1989), Watson (1998) and Clark et al. (2001). 226 Blake et al.

regionally distinctive Falls Leucogneiss (Parker, 1979; Farrar, originally thought to be an Alleghanian pluton intruded along the 1985a, 1985b; Stoddard et al., 1991; Horton et al., 1994; Blake et Nutbush Creek–Lake Gordon fault system, its U-Pb zircon age of al., 2001). These rocks lie within and east of the Nutbush Creek– 542 ± 3.1 Ma (Caslin, 2001) precludes that possibility. Lake Gordon fault system, an integral member of the Eastern Farrar (1999) and Farrar and Owens (2001) proposed that Piedmont fault system. To the northeast of the batholith, between bodies of the Falls Leucogneiss, based upon mineralogy and the Nutbush Creek–Lake Gordon fault system and Macon fault major and trace element characteristics, represent peralkaline zone, the anticlinorium hinge zone contains pelitic and mafi c to granite intruded into the thinned Laurentian margin at the begin- felsic protoliths that are now schist, paragneiss, and orthogneiss ning of the Iapetan rifting cycle ca. 600 Ma. These authors infer (Farrar, 1985a, 1985b; Sacks, 1999). Below, these two domains that the leucogneiss intruded the western edge of the Goochland of rocks grouped as the Raleigh terrane across the Rolesville terrane and was subsequently deformed by Alleghanian ductile batholith are discussed separately, and the possibility is raised dextral-slip faults. This is problematic because the Laurentian that they may actually constitute two distinct terranes. margin had entered a rift-drift phase by ca. 550 Ma. (Meert and In the southwestern Raleigh terrane, there are complex Torsvik, 2003). intrusive relationships among medium- to coarse-crystalline bio- Mesozoic brittle faults truncate the Falls Leucogneiss at tite and hornblende-biotite tonalitic to granitic orthogneiss and its southern termination south of Raleigh (Heller et al., 1998). fi ne- to medium-crystalline, more mafi c biotite ± hornblende ± Along its northern exposures, in the Kittrell and Henderson clinopyroxene gabbroic to dioritic orthogneiss, amphibolite, 1:24K Quadrangles, interlayered mafi c to felsic orthogneiss and and biotite ± white mica schist. These relationships produce a more minor metamorphosed ultramafi c rocks, some of which distinctive, variably migmatitic aspect in the Raleigh Gneiss. are considered to be layers within the Raleigh Gneiss, have been Multiple pulses of concordant to discordant intrusions may be mapped on both sides of the Falls Leucogneiss (Stoddard et al., seen at cm- to m-scales, forming melanocratic to leucocratic, dis- 2002; Blake and Stoddard, 2004). Many of these same gneisses continuous layers. Small, map-scale bodies of meta-ultramafi c also record ductile fault strain. At their northern extent in Hender- actinolite-chlorite rock are exposed in the northern portions of son, North Carolina, both the Falls Leucogneiss and the Raleigh the lithodeme (Robitaille, 2004; Stoddard et al., 2002). Gneiss terminate against Alleghanian granitoids between strands Mafi c gneiss and schist appear to have formed earlier than of the Nutbush Creek–Lake Gordon fault system. more intermediate to felsic gneiss. The mafi c rocks form thick Farrar (1984, 1985a, 1985b) interprets rocks and metamor- layers, thin selvages or enclaves within more differentiated fel- phic mineral assemblages of the Raleigh terrane as correlative sic layers. Locally, felsic gneiss layers, and weakly foliated to with the Grenville Goochland terrane in the eastern Piedmont unfoliated aplite to pegmatitic granite, likely related to the Roles- of Virginia. The Goochland terrane, thought to be a portion of ville batholith, form dikes and veins that truncate sill-like mafi c the rifted eastern margin of Laurentia, was thrust westward to felsic gneiss. In other exposures, generally farther east, these during Paleozoic collisional deformation. Polymetamorphic granitic rocks dominate, but biotite gneiss, hornblende ± biotite microstructures north and northeast of the Rolesville batho- gneiss, and amphibolite layers, enclaves, and selvages persist, lith indicate that a greenschist to middle amphibolite facies and with sill-like granitic layers form a lit-par-lit appearance. event appears to overprint an earlier metamorphic event that Accordingly, Parker (1979) called the Raleigh Gneiss “injected reached at least the sillimanite zone (Farrar, 1985b; Stoddard gneiss and schist.” Like him, we interpret this zone to show pro- et al., 1991; Sacks, 1999). This earlier metamorphic event may gressive mixing of younger granite with older country rock. In be correlative with metamorphic mineral assemblages of the addition, locally intense ductile dextral-slip deformation over- Goochland terrane. prints the Raleigh Gneiss and associated younger granitoid rocks. However, geochemical data indicate that metamorphosed The deformation is more apparent toward the northern end of the mafi c rocks of the Raleigh Gneiss group with arc-related basalts outcrop belt in the Kittrell and Henderson 1:24K Quadrangles on trace-element tectonic discrimination diagrams (Parnell et as compared to its southern equivalents in the Lake Wheeler and al., 2006a; Parnell, 2012). Additionally, the ca. 542 Ma zircon Raleigh West 1:24K Quadrangles (Stoddard et al., 2001; Blake date for the Falls Leucogneiss correlates with Stage III plu- and Stoddard, 2004; Blake, 2008). tonism in the Carolina and Charlotte terranes (Hibbard et al., One prominent pluton in the Raleigh Gneiss is the Falls Leu- 2002). The bulk of the Raleigh Gneiss appears to represent Neo- cogneiss. This leucogranitic orthogneiss forms a narrow, sheet- proterozoic to early Paleozoic, multiply intruded infrastructure like pluton 75 km long and up to 2.2 km wide along much of the to the Carolina Zone that was deformed, metamorphosed and length of the Crabtree terrane-Raleigh terrane boundary (NCGS, intruded by granitoids during the late Paleozoic Alleghanian 1985; Farrar, 1985a, 1985b; Horton et al., 1994). The pluton, orogeny. Limited isotopic dating tends to support this conten- which records a penetrative L-tectonite fabric and strong linear tion (Owens and Buchwaldt, 2009). We also conclude that the magnetic anomaly, is located primarily along the western margin Falls Leucogneiss is a deformed, metaplutonic member of the of the Raleigh Gneiss (Druhan et al., 1994; Horton et al., 1994). Raleigh Gneiss. Near Raleigh, the leucogneiss intrudes Raleigh Gneiss amphib- While the original affi nity of the Raleigh terrane remains olite layers (Blake et al., 2001). Although the leucogneiss was debatable, recent mapping indicates that the Nutbush Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 227

Creek–Lake Gordon fault system, deformed Alleghanian Suprastructural Carolina Terrane granitoids, and the Hylas fault actually separate it from the Goochland terrane (Sacks, 1999). No petrographic correla- The easternmost Carolina terrane is the westernmost and tion of granulite facies assemblages of the Virginia Gooch- structurally highest assemblage of supracrustal rocks that span land terrane has been established with those in the Raleigh the eastern-to-central Piedmont transition along the western Gneiss southwest of the Rolesville batholith and east of the fl ank of the Wake-Warren anticlinorium. The Triassic Deep Nutbush Creek–Lake Gordon fault system (Stoddard, 1989; River rift basin and associated normal-slip Jonesboro fault and see also Blake, 1986; Heller, 1996; Grimes, 2000; Robitaille, FCFZ separate these rocks from the main portion of the Carolina 2004). Mineral assemblages of the Raleigh Gneiss best cor- terrane in the central Piedmont (Fig. 1, 2, and 4; Secor et al., relate with an Alleghanian greenschist to mid-amphibolite 1983; Butler and Secor, 1991; Hibbard et al., 2002). In general, facies metamorphism (Russell et al., 1985). The migmatitic the easternmost Carolina terrane contains felsic to mafi c, and aspect and mafi c components of the Raleigh Gneiss southwest locally ultramafi c plutonic rocks, and felsic to mafi c volcanic and of the batholith also appear different from meta-igneous and volcaniclastic rocks now metamorphosed to the lower to upper metasedimentary lithologies northeast of the batholith. greenschist facies and chlorite-biotite-garnet zone (Farrar, 1985a, As a consequence of these fi ndings, we here propose 1985b; Stoddard et al., 1991). A prograde west-to-east gradient that high-grade metamorphic rocks lying between the Nut- in regional metamorphism across the easternmost Carolina ter- bush Creek–Lake Gordon fault system and Macon fault zone, rane increases metamorphic grade from the chlorite-biotite zone which have been heretofore depicted on most regional maps of the greenschist facies to the biotite-kyanite zone rocks of the as belonging to the Raleigh terrane, may actually constitute a amphibolite facies. This metamorphic gradient overprints earlier separate, eastern terrane, herein called the Warren terrane. The metamorphism. It also marks the Alleghanian metamorphic over- newly defi ned Warren terrane is considered to be distinct from print that defi nes the western fl ank of the Wake-Warren anticlino- its Raleigh terrane neighbor to the west (Fig. 2). In addition to rium, the western limit of the Nutbush Creek–Lake Gordon fault gneiss located north of the Rolesville batholith and east of the system, and the east-to-west transition from mid-to-upper crustal Nutbush Creek–Lake Gordon fault system (and previously des- rocks rock types and structures. It also corresponds to the eastern- ignated as part of the Raleigh Gneiss), this new terrane includes to-central Piedmont transition (Fig. 2). the Macon Formation of Farrar (1985a, 1985b) and various schist Field and petrographic relationships among the metamor- and gneiss units mapped by Sacks (1996a, 1996b, 1996c; see also phosed mafi c to felsic fl ows, tuffs, dikes, volcaniclastic rocks, and Stoddard et al., 2009, 2011). Lithologies include layered biotite, their subvolcanic plutons refl ect the exposure of multiple centers hornblende, and hornblende-biotite orthogneiss similar to parts of bimodal volcanism that are Neoproterozoic to early Paleozoic of the Raleigh Gneiss, but also include pelitic and white mica in age. The metamorphosed volcanic and plutonic rocks share quartzitic schist and other less common rock types. The Raleigh similarities in mineralogical and geochemical characteristics terrane is defi ned as the highly strained units of Raleigh Gneiss (Blake et al., 2001; Parnell et al., 2006a; Parnell, 2012). Although and Falls Leucogneiss that lie within the Nutbush Creek–Lake these rocks are exposed at different metamorphic grades due to Gordon fault system, east of the Crabtree terrane, and west of the folding and faulting, similarities in lithology, protoliths, and geo- Warren terrane. chemical signatures suggest links between volcanogenic rocks The justifi cation for defi ning a new Warren terrane is based of the easternmost Carolina terrane and those of the Falls Lake, on the (1) recognition of the regional signifi cance, along-strike Crabtree, Spring Hope, and the newly defi ned Raleigh and War- extent, and correlations among individual strands within the ren terranes (Stoddard et al., 1996). Easternmost Carolina terrane Nutbush Creek–Lake Gordon fault system, and (2) occurrence rocks appear to be generally correlative with metamorphosed of a considerable proportion of rocks having supracrustal ori- Neoproterozoic to Cambrian calc-alkaline volcanic, volcanicla- gin in this northeastern part of the eastern Piedmont north of the stic, and plutonic rocks in the Carolina terrane west of the Deep Rolesville batholith. Rock units having probable supracrustal River basin that are inferred to be the products of island-arc mag- protoliths include one- and two-mica schist, locally having gar- matism above a peri-Gondwanan, perhaps western Amazonia, net, chloritoid, sillimanite, kyanite, and rare staurolite or corun- subduction zone (Hibbard et al., 2002; Parnell et al., 2006a; Pol- dum as key index minerals. In addition, quartz-kyanite rock and lock and Hibbard, 2006; Pollock, 2007; Rhodes et al., 2011). quartz-sillimanite rock may be high-grade metamorphic equiva- At the northern termination of the Durham sub-basin south lents of aluminous, hydrothermally altered felsic metavolcanic of Oxford, eastern Piedmont rocks merge with similar-grade rocks such as pyrophyllite-bearing units of the Carolina Zone. rocks of the Virgilina sequence of the main Carolina terrane in Future mapping will also test whether metamorphic rocks north the central Piedmont (Glover and Sinha, 1973; Hadley, 1973; of the Rolesville batholith in the Warren terrane are lithologically Harris and Glover, 1988; Hibbard et al., 2002) across the FCFZ or tectonically separate from those in the southwestern portion of (Blake et al., 2007). Complex syn-depositional interlayering the Warren terrane adjacent to the southern end of the batholith of felsic and mafi c pyroclastic rocks, fl ows, and their volcani- (Fig. 2). We will examine rocks of the Warren terrane at Stops 1 clastic sedimentary equivalents are primarily exposed west of and 2 of the fi eld trip. the fi eld trip area in the central and western Lake Michie 1:24K 228 Blake et al.

Quadrangle. A suite of metamorphosed gabbro and calc-alkaline have a mixed fl ow and clastic sedimentary origin. This green- granitoids, including the informal Stem tonalite-granodiorite stone appears to be wall rock to both the Gibbs Creek and Tabbs pluton and Oxford granite plutons of this fi eld trip, intrudes and Creek complex metagranitoids. includes small and large enclaves of these metamorphosed vol- Traversing eastward and northeastward across the suite canic and sedimentary rocks. These plutons become the primary however, greenstone outcrops become very fi ne-crystalline rock types exposed from the eastern Lake Michie 1:24K Quad- metagabbro. Swarms of metagranitoid dikes invade both green- rangle, across the northern Stem 1:24K Quadrangle, and into the stone types and produce an array of enclave relationships. In Wilton and Oxford 1:24K Quadrangles (Fig. 4; Hadley, 1973, many outcrops, metagabbro enclaves and contacts between 1974; McConnell, 1974; McConnell and Glover, 1982; Harris the metagabbro and metagranitoid preserve rounded to lobate and Glover, 1988). shapes rather than angular boundaries; this may indicate a warm, North of Oxford, the Carolina terrane is essentially unbro- malleable material behavior for the mafi c plutons during felsic ken across the eastern-to-western Piedmont transition, although injection (Grimes, 2000). the northern tip point for the FCFZ (the westernmost of the two The Vance County pluton is a metamorphosed granodiorite major Mesozoic faults that bound the northeast border and sed- to trondhjemite batholith having a ca. 571 Ma zircon crystalli- imentary portion of the Triassic Durham sub-basin) has yet to zation age (LeHuray, 1989; Farrar, 1985a; Druhan et al., 1994). be found. High-strain crystalline rocks along strike of the FCFZ In the Henderson, Townsville, and Middleburg 1:24K Quadran- continue north from the Oxford 1:24K Quadrangle to at least the gles, it consists of medium- to coarse-crystalline, locally por- central Stovall 1:24K Quadrangle (Parnell, 2012). phyritic biotite ± hornblende tonalite, granodiorite, granite and In the north-central Grissom 1:24K Quadrangle, the FCFZ trondhjemite that commonly contains greenish saussuritized apparently terminates against the Jonesboro fault, which extends plagioclase and blue quartz. Enclaves of fi ner-crystalline foli- northeastward from the Triassic basin, further complicating the ated and unfoliated rocks are common. Westernmost exposures lithologic and structural transition from the eastern-to-central are less deformed, but toward the Nutbush Creek–Lake Gordon Piedmont. The Jonesboro fault coincides with the outcrop trace fault system to the east, outcrops of the Vance County pluton and overprints the western portion of the Nutbush Creek–Lake display increasing intensity of deformation that produced pro- Gordon fault system. There, the Jonesboro fault separates lower tomylonitic, mylonitic, ultramylonitic, and phyllonitic rocks. greenschist facies Carolina terrane metaplutonic rocks to the west The Tabbs Creek complex and Vance County pluton are in from their amphibolite facies Falls Lake, Crabtree, and Raleigh fault contact with the Crabtree and Raleigh terranes and with terrane equivalents to the east. deformed granitic rocks across the Nutbush Creek–Lake Gor- North of the truncation of the FCFZ against the Jonesboro don fault system adjacent to the North Carolina–Virginia state fault zone in the Wilton, Oxford, Kittrell, Henderson, Townsville, line (Druhan et al., 1994; Grimes et al., 1997; Grimes, 2000; and Middleburg 1:24K Quadrangles (Figs. 2, 3, and 4), metaplu- Blake et al., 2001). tonic rocks dominate the Carolina terrane. From south to north, the major plutonic bodies are the Gibbs Creek pluton, Tabbs Pennsylvanian-Permian Granitoid Rocks Creek complex, and the Vance County pluton, all of tonalitic to granodioritic bulk composition (Parker, 1963; Cook, 1963; Car- The Rolesville batholith is a large, composite granitoid penter, 1970; Hadley, 1973; Farrar, 1985a; Grimes, 2000; Parnell intrusion that lies generally along the hinge zone of the Wake- et al., 2006b; Stoddard et al., 2002; Blake et al., 2003a). The east- Warren anticlinorium, just east of the fi eld trip area (Figs. 1 and ern boundary of the Carolina terrane actually lies to the east of the 2). Field evidence indicates that plutons of the Rolesville batho- FCFZ along the western boundary of the Nutbush Creek–Lake lith injected during or after the peak of regional metamorphism, Gordon fault system. Between the FCFZ and Nutbush Creek– and very limited radiometric age-dates indicate that they crystal- Lake Gordon fault system, these Carolina terrane metaplutonic lized and cooled during the Pennsylvanian and Permian periods rocks are complexly dissected by a network of anastomosing, (Fullagar and Butler, 1979; Horton and Stern, 1994; Schneider ductile-brittle normal-slip fault zones. and Samson, 2001). The Gibbs Creek pluton, a metamorphosed porphyritic to Previous studies dealing with the Rolesville batholith include equigranular tonalite and granodiorite, contains many cm- to those of Parker (1968), Becker and Farrar (1977), Farrar (1985a, m-scale enclaves of greenstone, and foliated and folded amphib- 1985b), Speer (1994), Speer et al. (1994), and Speer and Hoff olite and granitoid, as well as four map-scale meta-ultramafi c (1997). Speer (1994) has demonstrated that, at least in the Raleigh bodies of serpentinite and talc + actinolite + chlorite rock up to 1:100K sheet, granitoid phases of the Rolesville batholith may several km long. Along its northern perimeter, the Gibbs Creek be distinguished, based upon petrographic features, enclaves, and pluton intrudes greenstone, metagabbro, and more dominant fi eld relationships. Mapping in the Henderson 1:100K sheet has metatonalite to metagranodiorite, collectively grouped as the been able to continue that approach, and has revealed a much Tabbs Creek complex (Grimes, 2000; Parnell et al., 2006b; Par- more extensive plutonic compositional range than heretofore rec- nell, 2012). Locally, greenstone in the complex preserves relict ognized for the batholith, indicated by the occurrence of small basaltic and conglomeratic textures suggesting portions may pods of granodiorite, quartz diorite, diorite, and gabbronorite Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 229

within the western and perhaps deeper (?) portion of the batholith from the Ruin Creek gneiss and foliated felsic gneiss of the Crab- (Gaughan and Stoddard, 2003; Stoddard, 2011). tree terrane (Figs. 2 and 3). In the Wilton 1:24K Quadrangle, Several smaller Pennsylvanian and/or Permian granitic plu- the Jonesboro fault truncates a portion of the Nutbush Creek tons are present throughout the eastern Piedmont (Speer, 1994; fault zone. South of the Jonesboro fault in the Creedmoor and Horton et al., 1994). One of the largest of these, the Wise pluton, Bayleaf 1:24K Quadrangles, the western boundary of the Falls lies mainly in the unmapped Warrenton 1:24K Quadrangle, just Lake terrane with the easternmost Carolina terrane is a ductile to the east of the fi eld trip route. The Wise granite is a medium- normal-slip fault informally named the Upper Barton Creek fault crystalline, two-mica granite within the fi eld trip area and is zone (Horton et al., 2004). Down-dip-oriented fabric elements considered to be a late syn-kinematic to post-kinematic pluton of Permo(?)-Mesozoic fault zones (Hames et al., 2001) may (Farrar, 1985a, 1985b; Sacks, 1996a). Alleghanian dextral-slip overprint the ductile dextral elements of the Nutbush Creek fault deformation ascribed to the Nutbush Creek–Lake Gordon fault zone, but fi eld relationships are equivocal and additional map- system overprints granitoid rocks at the northern and northwest- ping is needed. ern margins of the Rolesville batholith across a corridor several From the Raleigh West 1:24K Quadrangle south to Harnett km in width. Undeformed granite crosscuts mylonitic granit- County where it has been mapped in detail, the Nutbush Creek oid gneiss, indicating that pulses of Pennsylvanian-Permian fault zone (formerly the Leesville fault zone) continues south- magma intruded both syn- and post-kinematically with respect to ward and separates greenschist-facies suprastructural rocks of Alleghanian deformation throughout the eastern Piedmont. the Cary sequence in the easternmost Carolina terrane from the Crabtree terrane to the east. The relocation and renaming of the Late Paleozoic Fault Zones Leesville fault zone to the Nutbush Creek fault zone is compatible with its mapped position between high grade and low grade The Alleghanian ductile dextral-slip fault zones crosscutting rocks north of the Jonesboro fault. The Nutbush Creek fault zone north-central North Carolina defi ne the individual high-strain ele- continues south to at least the south side of the Cape Fear River ments of the Eastern Piedmont fault system and include from east before it and the easternmost Carolina and Crabtree terranes are to west, the Gaston Dam, Hollister, Macon, and Middle Creek obscured by Coastal Plain sedimentary rock cover in the Mamers (?) fault zones on the eastern fl ank and within the hinge zone and Lillington 1:24K Quadrangles. of the Wake-Warren anticlinorium. On the western fl ank and in As such, in the Henderson 1:24K Quadrangle east of the its type locality within the Kerr Lake Recreation Area (Casade- Nutbush Creek fault zone, recent mapping indicates that the fault vall, 1977), the historically known Nutbush Creek fault zone is zone which has been previously identifi ed as the Nutbush Creek is defi ned as the dextral-slip fault zone that separates amphibolite- actually a different zone of high strain within the Nutbush Creek– facies infrastructural Raleigh terrane rocks to the east from the Lake Gordon fault system herein renamed the Neuse River fault greenschist-facies suprastructural Carolina terrane rocks to the zone (Fig. 2). From the northeastern Henderson 1:24K Quad- west. Reconnaissance mapping from the type locality of the Nut- rangle where they truncate against highly deformed Alleghanian bush Creek fault at the Virginia state line southward originally granitoids of the Rolesville batholith, the Crabtree terrane, Neuse designated the southern extension of the fault to be the zone of River fault zone, and a thin sliver of the redefi ned Raleigh terrane highest observed strain. including the Raleigh Gneiss and the Falls Leucogneiss continue However, NCGS STATEMAP results over the past 10 years southward to the Wilton 1:24K Quadrangle. have identifi ed other zones of high strain that were assigned vari- There, the Neuse River fault zone overprints the eastern por- ous fault names (e.g., Leesville fault zone). Our current mapping tion of the Crabtree terrane and the Alleghanian Wilton granite has necessitated some renaming of individual fault strands across pluton that intrudes it (Figs. 2, 3 and 4). The Wilton pluton in the eastern-to-central Piedmont transition to retain consistency turn, truncates the northern boundary between the Falls Lake in the original defi nition of fault strands based upon fi eld rela- and Crabtree terranes which is the dextral-slip Falls Lake fault tionships while maintaining the established terrane terminology. zone. This strand of the Nutbush Creek–Lake Gordon fault sys- Using recent mapping, the true southward extension of the Nut- tem continues southward from the Wilton pluton to the north- bush Creek fault zone from its type locality lies to the west of its ern Raleigh West 1:24K Quadrangle where it merges with the currently defi ned location (e.g., Stoddard et al., 1991; Druhan et newly redefi ned Nutbush Creek fault zone. It is likely that both al., 1994), on the western fl ank of the Wake-Warren anticlino- the Falls Lake and Nutbush Creek faults zones are overprinted by rium, as originally suggested by Farrar (1985a, 1985b). The the Upper Barton Creek normal-slip fault zone here. newly named terrane-bounding strands now include, from east to From the Pennsylvanian Wilton granite in the Wilton 1:24K west, the Lake Gordon, Neuse River, Falls Lake, and regionally Quadrangle south to the Lake Wheeler 1:24K Quadrangle in known Nutbush Creek fault zones (Fig. 2; Hatcher et al., 1977; southern Wake County, the Neuse River fault zone (former loca- Bobyarchick, 1981; Sacks 1999; Stoddard et al., 2009). tion of the Nutbush Creek) marks the boundary between the In the John H. Kerr Dam, Middleburg, Townsville, Hender- amphibolite-facies infrastructural Crabtree and Raleigh terranes. son, Kittrell, and Wilton 1:24K Quadrangles, the Nutbush Creek The L>S tectonite of the Falls Leucogneiss still characteristically fault zone separates metaplutonic rocks of the Carolina terrane marks the location of this high-strain terrane boundary along 230 Blake et al. most of its length. In the southern Lake Wheeler 1:24K quadran- and local full grabens along the Atlantic margin of North Amer- gle, the Neuse River fault zone joins with the Lake Gordon fault ica. The Deep River basin is the southernmost exposed of these zone and terminates the Raleigh terrane. South of this fault zone basins. During rifting, the basin fi lled with a variety of Trias- branch point, the Neuse River fault zone (former Nutbush Creek) sic clastic sediments, their depositional environments strongly continues southward as the dextral-slip fault zone separating the controlled by local basin tectonics. Alluvial fan complexes pro- infrastructural Crabtree terrane to the west from the suprastruc- graded westward into the basin from its topographically higher tural Spring Hope terrane to the east (Fig. 2). faulted margins. Sediment was transported north and south The Lake Gordon fault zone, originally defi ned by Hor- along the basin axis by meandering river systems and depos- ton et al. (1993a,1993b) and Butler and Horton (1995), trends ited in large alluvial plains. Fresh-water lakes formed in basin northeast-southwest through southern Virginia and lies parallel depocenters, accumulating deltaic (delta), lacustrine (lake), and to and east of the Nutbush Creek fault zone (Sacks, 1999). The paludal (swamp) deposits. deformed Pennsylvanian Buggs Island granitoid pluton sepa- The deposits of the Deep River basin were buried and lith- rates the two fault zones in the southern Piedmont of Virginia ifi ed, and are now recognized as the Chatham Group, part of the and defi nes a much narrower Nutbush Creek–Lake Gordon fault Newark Supergroup as defi ned by Olsen (1978), Luttrell (1989), system than in North Carolina. The Lake Gordon fault zone and Weems and Olsen (1997). The Chatham Group in the Deep continues into North Carolina and marks the boundary between River basin consists of varying amounts of conglomerate, sand- highly deformed Pennsylvanian-Permian granitoid plutons and stone, siltstone, claystone, shale, coal, and small amounts of amphibolite facies, infrastructural schist and gneiss of the newly limestone and chert. Bedding generally dips from west to east, named Warren terrane just south of the Virginia–North Carolina but local variations are common, especially near faults and state line. It continues south from the John H. Kerr Dam 1:24K dikes. Thus, the lowermost (oldest) strata typically occur on the Quadrangle separating individual deformed plutons of a larger, western side of the basin and the uppermost (youngest) strata composite Alleghanian Rolesville batholith. South of the Kittrell occur on the east. 1:24K Quadrangle to its branch point with the Neuse River fault The Deep River basin is a north- to northeast-trending half zone in the Lake Wheeler 1:24K Quadrangle, the Lake Gordon graben. The Jonesboro fault, a west-dipping high-angle normal fault zone separates the Raleigh and Warren terranes and helps fault, borders the basin on its east side (Campbell and Kim- defi ne the high strain character of the western fl ank of the Wake- ball, 1923). This fault separates the Triassic sedimentary rocks Warren anticlinorium (Fig. 2) from crystalline rocks of the western fl ank of the Wake-Warren Strands of the Nutbush Creek–Lake Gordon fault system, anticlinorium (Parker, 1979; North Carolina Geological Survey, as newly defi ned, appear to overlap along much of the length 1985; Blake et al., 2001). The total amount of displacement of the western fl ank of the Wake-Warren anticlinorium, thus along the fault is unknown, but a minimum estimate of 3.0– potentially constituting an along-strike zone of dextral-slip 4.5 km of dip-slip displacement is proposed, depending on loca- releasing offset. Kinematic indicators in rocks affected by these tion (Campbell and Kimball, 1923; Reinemund, 1955; Bain and faults record a progressive ductile strain history having transi- Harvey, 1977; Parker, 1979; Bain and Brown, 1980; Hoffman tional strike-slip and dip-slip components during the late Paleo- and Gallagher, 1989). Bain and Brown (1980) suggested the zoic and early Mesozoic, suggesting an evolution from crustal Jonesboro fault is actually a fault zone, characterized by “step- transpressional (contraction or shortening) to dextral simple faulting” along numerous individual faults. Rider blocks are shear strain, and then, perhaps to dextral transtension and fi nally inferred to occur between these faults. Clark (1998) observed to extension. The transtensional component may have enabled that the Jonesboro fault plane itself is extremely sharp, com- the injection of deformed and undeformed magmatic facies of the monly with a 1–3 m wide gouge zone of clay and foliated brec- Pennsylvanian-Permian Rolesville batholith and similar Allegha- cia in the footwall. nian orogeny plutons along the length of the Wake-Warren anti- Several intra-basinal faults, both synthetic and antithetic clinorium. The extensional component resulted from Triassic to the Jonesboro fault, are also recognized throughout the basin rifting and facilitated Jurassic diabase intrusions. (Wooten et al., 2001). Along the western margin of the basin, Tri- assic sedimentary rocks unconformably overlie Neoproterozoic Mesozoic Rift Basin and Magmatism and Cambrian metavolcanic and metasedimentary rocks of the Carolina terrane (Butler and Secor, 1991). Locally, minor faults Early Mesozoic rocks in the eastern Piedmont of North Car- also form the basin boundary along the western border. olina consist of two types: (1) Triassic sedimentary rocks of the From north to south, the Deep River basin is subdivided into Deep River rift basin, and (2) Early Jurassic diabase dikes and three smaller basins, the Durham, Sanford, and Wadesboro sub- sills intruding both the Triassic sedimentary rocks and the crys- basins, respectively. The boundaries of these smaller, component talline rocks of the western fl ank. sub-basins are undefi ned. The width of the Deep River basin dra- The Deep River basin formed as a result of late Paleozoic matically narrows at the Colon cross-structure, a basement high (?) to early Mesozoic rifting of the supercontinent Pangea (Fig. that separates the Durham sub-basin from the Sanford sub-basin 5). This rifting created a series of irregularly shaped half- grabens (Campbell and Kimball, 1923). Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 231

The Colon cross-structure is well constrained by fi eld map- Watson (1998) extended some of the lithofacies of Hoff- ping and seismic refl ection data. Analyses of these data suggest man and Gallagher (1989) into the central Durham sub-basin in it formed by differential subsidence of the Durham and Sanford the Green Level 1:24K Quadrangle. Clark (1998) also utilized sub-basins (Reinemund, 1955; Bain and Harvey, 1977; Dittmar, the lithofacies system in the southern Durham sub-basin in the 1979). Slightly different lithologies occur on either side of the Cary, New Hill, Apex, and Cokesbury 1:24K Quadrangles. Clark Colon cross-structure, suggesting it may have acted as a barrier found two lithofacies of Hoffman and Gallagher (1989), Trcs to sedimentation. A similar structure, the Pekin cross-structure, (sandstone) and Trcsc (pebbly sandstone), were so intermixed has been proposed between the Sanford and Wadesboro sub- in map pattern that he combined them into one mappable unit, basins. The existence of the Pekin cross-structure is speculative Trcs/sc (interbedded sandstone and pebbly sandstone). All other due to a thin veneer of Atlantic Coastal Plain sedimentary rocks map units are consistent with Hoffman and Gallagher (1989) and that blankets the area, as well as a lack of well constrained sub- Watson (1998). surface data. A complete description of the lithofacies of the Durham sub- Bain and Harvey (1977) proposed the fi rst map units internal basin, as well as the Sanford sub-basin to the south, can be found to the Durham sub-basin based on reconnaissance-level mapping. in Clark et al. (2001). The NCGS (1985) later consolidated these into four facies for the State Geologic Map. However, during detailed geologic mapping Early Jurassic Intrusive Rocks of the central Durham sub-basin (Southeast and Southwest Dur- ham 1:24K Quadrangles), Hoffman and Gallagher (1989) found Early Jurassic diabase intrusions occur throughout the North these facies, as defi ned, inadequate for describing the rocks in Carolina Piedmont, but are most concentrated in the Deep River their map area. They found that several of these facies could rift basin. These rocks belong to a large family of mafi c rocks be subdivided even further into more specifi c map units. They termed the eastern North America early Mesozoic mafi c prov- subsequently adopted the lithofacies system of nomenclature of ince (ENA province) and are interpreted to have resulted from Smoot et al. (1988) for consistency with other geologic mapping the breakup of Pangea in the early Mesozoic (Ragland, 1991). throughout the Newark Supergroup. The rocks typically occur as northwest-trending, steeply dipping As a result of their mapping, Hoffman and Gallagher (1989) to vertical, gray to bluish-black, slightly to severely weathered, identifi ed seven distinct lithofacies in the central Durham sub- fi ne- to medium-crystalline diabase. A second set of north-south basin. These lithofacies were grouped in three lithofacies asso- trending dikes exists in the central North Carolina Piedmont. ciations, labeled Lithofacies Association I (LA I), Lithofacies More rare are a few sill-like or lopolithic sheets exposed in the Association II (LA II), and Lithofacies Association III (LA Deep River basin north of Durham. III), in ascending stratigraphic order. Olsen (1997) proposed an All of the North Carolina dikes are mafi c in composition, unconformity may exist between LA I and LA II based on ver- except for a few felsic dikes in the extreme northeastern Piedmont tebrate fossil assemblages. An intertonguing relationship exists reported by Stoddard et al. (1986), Stoddard (1992), and Sacks between LA II and LA III. (1999). A thorough discussion of the dike petrology is provided In general, LA I contains interbedded sandstone and silt- by Ragland (1991). Previous K-Ar and Ar-Ar dating attempts stone and is interpreted as braided stream deposits. LA II also resulted in a wide range of ages between 160 and 203 Ma; contains interbedded sandstone and siltstone, but is interpreted however, recent 40Ar/39Ar work by Hames (2000, personal com- as a meandering fl uvial system surrounded by a vegetated fl ood- mun.) suggests an Early Jurassic age of 201 ± 5 Ma. plain. LA III contains poorly sorted sandstone, pebbly sandstone, Ebasco Services, Inc. (1975) conducted a detailed inves- and conglomerate. LA III is interpreted as alluvial fan complexes tigation of diabase dikes during construction of the Shearon characterized by broad, shallow channels having high sediment Harris nuclear power plant in southwestern Wake County. Sev- concentrations and locally, high-energy debris fl ows. eral of these dikes were observed to be laterally offset 0.5– The terminology used by Hoffman and Gallagher (1989) 4 m by the Harris fault, a south-dipping normal fault identifi ed for individual lithofacies (Smoot et al., 1988) names each during power plant construction. Ebasco Services, Inc. also individual lithofacies by combining its age, group, and lithol- conducted a magnetometer survey of a large (50-m-wide) dike ogy into one map unit abbreviation. The prefi xes for age (Tr = that crossed the Jonesboro fault. The resulting geologic map Triassic) and group (c = Chatham Group) are common to all suggested 300 m of right-lateral offset of the dike by the Jones- Triassic lithofacies in the Durham sub-basin. The remain- boro fault (Bain and Harvey, 1977). These fault-dike observa- der of the unit name is reserved for the dominant lithology tions are important in that they show Jurassic dikes offset by (i.e., si = siltstone, s = sandstone, sc = pebbly sandstone, c = presumably Triassic faults. If the Early Jurassic age by Hames conglomerate). Interbedded lithologies are separated by a et al. (2001) is correct, then tectonic activity (rifting) clearly slash, dominant lithology given fi rst (i.e., s/c = interbedded continued past the Early Jurassic. The minimum age for this sandstone and conglomerate). Similar lithofacies of differ- activity is unconstrained. ent lithofacies associations are notated by subscript numerals The only other rocks in the area are Late Cretaceous marine

(i.e., Trcs/si1 versus Trcs/si2). sediments of the Atlantic Coastal Plain that uncomformably 232 Blake et al.

overlie the Jonesboro fault. However, no attempts have been made Stop 1. Layered Mafi c Gneiss of the Warren Terrane to document fault offset at these locations. Snipes et al. (1993) Location: Abandoned sewer line excavations and roadway, north and Stieve and Stephenson (1995) studied a similar Triassic rift side of Fishing Creek, downstream from Manson-Axtell Road basin, the Dunbarton basin, along the South Carolina–Georgia bridge, extending ~300 m downstream to where the creek bends border. The Dunbarton is buried by ~350 m of Late Cretaceous to the right (south); southeastern corner of the quadrangle. and Tertiary Atlantic Coastal Plain sediments. Seismic refl ection Map: Middleburg 1:24K Quadrangle. and borehole data clearly show the basin-bounding normal fault, the Pen Branch fault, was reactivated during the Late Cretaceous Metamorphic rocks east of the Lake Gordon fault zone as a reverse fault, offsetting the Coastal Plain sedimentary units include a mix of gneiss and schist that have been considered by as much as 30 m. It is therefore possible that studies could to be parts of the Raleigh Gneiss by Farrar (1985a, 1985b) and reveal similar late Mesozoic–early Cenozoic tectonic activity other workers (Fig. 3). At Stop 1, rocks are exposed along Fish- along the Jonesboro fault in North Carolina. ing Creek and along a parallel roadway that was excavated for a sewer line during the early 1970s. The line runs to a small, FIELD TRIP STOPS and now defunct, wastewater treatment facility located about one km downstream from the bridge. The project was intended Purpose and Objective to serve the planned community of Soul City, brainchild of civil rights leader Floyd B. McKissick. Legislation enacted during The purpose of this two-day fi eld trip is to provide (1) a the administration of President Lyndon Johnson made federal regional geologic synopsis of a portion of the north-central assistance available that allowed the initial development of Soul North Carolina Piedmont, and (2) a tectonic overview of City and its infrastructure, but economic conditions and politics some of the interrelationships among lithologic, metamor- prevented the concept from achieving fruition (see Strain, 2004; phic, structural, and magmatic components of the transition Biles, 2005). The property is now privately owned. from Pangean amalgamation to its initial breakup within the Here we are in a unit consisting primarily of mesocratic to Carolina Zone (Figs. 1 and 2). We will focus on a corridor melanocratic, medium- to coarse-crystalline, typically layered of 1:24K quadrangles mapped along the Alleghanian Nutbush hornblende and hornblende-biotite gneiss (Figs. 6A, 6B). Clino- Creek–Lake Gordon fault system and the northern Durham pyroxene is common, generally as a later phase and locally part sub-basin of the Triassic Deep River rift basin. A regional of a mineral assemblage showing granoblastic texture. Some of overview of the fi eld trip stops is provided on two composite the orthogneiss in this unit is clearly metagabbroic, having large geologic maps of the Henderson, Townsville, Middleburg, and relict plagioclase phenocrysts and a color index of ~50; mylonitic North Carolina portion of the Kerr Dam 1:24K Quadrangles overprint in places yields a porphyroclastic texture from the relict for Day 1 (Fig. 3) and the Oxford, Wilton, Stem, Lake Michie, plagioclase phenocrysts. In addition to green hornblende, biotite, Creedmoor, and Bayleaf 1:24K Quadrangles for Day 2 (Fig. intermediate plagioclase, and clinopyroxene, epidote/clinozoisite 4). Mileages were determined using the ruler tool in Google and titanite are common mineral constituents (Fig. 6C). Middle Earth©. All stops are georeferenced using latitude and longi- to upper amphibolite facies conditions are inferred, locally over- tude coordinates (WGS84). printed by hornblende hornfels facies. No orthopyroxene has been observed, and in thin section, clinopyroxene appears to have DAY 1. CHARLOTTE TO KERR LAKE AND formed after hornblende, indicating that at least at this stop, the THE NUTBUSH CREEK FAULT ZONE rocks did not achieve the granulite facies (Fig. 6D). Other layered portions are suggestive of a metasedimentary Directions to Stop 1. Depart the Charlotte Convention component. For example, this unit is in contact to the west with Center, driving north on E. Stonewall St. Turn left (west) on fi ne- to medium-crystalline quartzofeldspathic gneiss. The unit S. Church St, and then merge right onto I-277 North. Drive also contains fi ne- to medium-crystalline felsic gneiss ± biotite, 0.5 mile and merge right onto I-77 North. Travel 4 miles and very rare diopside-rich calc-silicate hornfels or granofels ± north on I-77 to the interchange with I-85 East at Exit 13. microcline. A major unit of white mica schist is exposed to the Merge right onto I-85 North and travel 185 miles to Exit 223 west of the quartzofeldspathic gneiss. In the northern Middleburg at Manson-Drewry Road (CR 1237). Turn right (east) from the and southern John H. Kerr Dam 1:24K Quadrangles, stringers of off-ramp traveling 0.9 miles to Manson. Turn right (south) on the white mica schist are associated with the hornblende-biotite U.S. 1 and drive 0.5 miles to Kimball Road. Turn left (east) gneiss unit. We will examine a garnet sillimanite white mica onto Kimball Road (Manson-Axtell Road, CR 1100), cross schist exposure at Stop 2. Orientations of gneissic layering are the railroad tracks, and travel 2.1 miles to Fishing Creek and quite variable here, but typically strike to the west of north and park on the right just north of the bridge. Walk carefully past dip moderately to steeply west or southwest. Early isoclinal folds the riprap to exposures along an old sewer line that follows are locally visible, overprinted by upright open folds. the north bank of the creek. This is Stop 1 [latitude 36.39908°, Locally, sills and dikes of granite and pegmatite, possibly longitude −78.26567°]. related to the Pennsylvanian-Permian Wise pluton just to the east, Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 233 are abundant. As such, exposures in this unit strongly resemble 1.2 miles, passing through Ridgeway, North Carolina. Turn left the Raleigh Gneiss near Raleigh, which has been referred to as an (north) on St. Tammany Road (CR 1210) and drive 3.6 miles, “injection complex” adjacent to the Rolesville batholith (Parker, passing over I-85 at Oine, North Carolina. Turn left (west) on 1979). In fact, ~200 m downstream from the bridge at Stop 1, Martin Road (CR 1217), drive 1.1 miles and turn right (north) near where a small tributary enters Fishing Creek, granitic injec- on Russell Union Road (CR 1206). Drive 0.9 miles to the bridge tions become abundant. However, in many other exposures, such over Smith Creek. Park and follow the path to the right (down- as some of the more upstream outcrops here, there is much less stream) on the north side of the creek to exposures on a low ridge felsic plutonic material. Here, the rock is layered amphibolite or at the edge of the fl oodplain. Stop 2 [latitude 36.50374°, longi- metagabbroic orthogneiss, and may perhaps be representative of tude −78.25078°]. a larger meta-igneous component to the protolith for parts of the Warren terrane. Some of this material, especially metaplutonic Stop 2. Pelitic Schist of the Warren Terrane protoliths may have originated as mafi c substrate for part of the Location: Low ridge on north side of Smith Creek ~0.15 miles Carolina Zone. The type area for the Raleigh terrane contains downstream (east) from Russell Union Road Bridge, southeast- little if any schistose, metasedimentary rocks and does not have ern corner of quadrangle. protoliths that resemble these Warren terrane rocks. Map: John H. Kerr Dam 1:24K Quadrangle. Directions to Stop 2. Depart Stop 1 and continue north on Manson-Axtell Road ~0.6 miles to Soul City. Turn right A map unit of pelitic mica schist is mapped continuously (east) on Liberation Road (CR 1113) and drive 2.1 miles to the from the southern edge of the Middleburg 1:24K Quadran- T-intersection. Turn left (north) on Axtell-Ridgeway Road and drive gle and into the southeastern corner of the John H. Kerr Dam 1.9 miles to U.S. Highway 1/158. Turn right (northeast) and drive 1:24K Quadrangle (Fig. 3). It lies mainly to the west of the

Figure 6. Outcrop and petrographic relationships at Stop 1. (A) Float block at Stop 1 showing thinly layered hornblende and hornblende-biotite gneiss with infolded ﬁ ne gneissic granitoid compositional layer. Hammer handle for scale. (B) Leu- cosome showing tight folding in maﬁ c gneiss at Stop 1. (C) Photomicrograph of hornblende-biotite orthogneiss from Stop 1. Hornblende+biotite-rich layer at lower right. Plane-polarized light, scale bar is 1 mm. (D) Photomicrograph of clinopyroxene-bearing hornblende metagabbro from the hornblende gneiss unit, about two km north of Stop 1. Pyroxene appears to have formed after hornblende, and is thus interpreted to be Alleghanian. Cross-polarized light. Scale bar is 1 mm. 234 Blake et al.

hornblende-biotite gneiss unit seen at Stop 1 and the intervening matic form along the foliation plane defi ned by white mica. One felsic gneiss unit, although there are some intercalations among unusual specimen, found as fl oat, consists of crenulated white these three lithologic units. The schist enters the southwestern mica schist with kyanite and fi brolitic sillimanite along the folia- portion of the Bracey 1:24K Quadrangle, where it was mapped tion, and porphyroblasts of corundum, one of which displays by Sacks (1996a) as part of his biotite gneiss unit. For most of pleochroic blue (var. sapphire) cores in thin section. its map length, the western margin of the schist carries a strong Farrar (1984, 1985a, 1985b) argued that sillimanite in the phyllonitic fabric and is in contact with granitoid mylonite. We schists of this area is Grenville in age (Mesoproterozoic), belong- interpret this contact as the eastern edge of the Lake Gordon fault ing to a granulite-grade assemblage overprinted by amphibolite zone and the Nutbush Creek–Lake Gordon fault system. assemblages of late Paleozoic age. It is possible that the prismatic The schist of this unit is typically medium-fi ne- to medium- sillimanite was the product of an early metamorphic event and crystalline, locally with large garnet porphyroblasts (to 1 cm); it is the fi brolitic variety may be the result of thermal overprint. The strongly foliated and locally strongly lineated. Common mineral later event is undoubtedly late Paleozoic in age; the age of the assemblages are white mica + sillimanite + garnet, white mica earlier event is unclear, but it also could be late Paleozoic. In thin + chlorite ± sillimanite ± garnet, white mica + biotite + garnet ± sections that we have examined which contain both kyanite and sillimanite ± kyanite ± chlorite ± tourmaline. Chlorite typically sillimanite, the sequence of their growth is ambiguous, except appears to be retrograde, and in some specimens occurs in clots for one specimen in which fi brolitic sillimanite appears to be the or sprays and may be pseudomorphic after an earlier porphyrob- later phase. Photomicrographs of samples from the pelitic schist lastic mineral. Sillimanite occurs most commonly in blocky pris- unit are shown in Figures 7A–7D.

Figure 7. Petrographic relationships in samples from the pelitic schist unit seen at Stop 2. (A and B) Photomicrographs of pelitic schist from outcrop in southern Middleburg 1:24K Quadrangle. Assemblage is white mica + garnet + biotite+ sillimanite+ chlorite. Sillimanite is prismatic and chlorite is retrograde, possibly pseudomorphic. Photo shows sillimanite prisms enclosed in white mica. (A) Plane-polarized light. (B) Cross-polarized light. Scale bar is 0.2 mm. (C and D) Photomicrographs from ﬂ oat sample within pelitic schist unit in south-central Middleburg 1:24K Quadrangle showing a large corundum porphyroblast, partially pseudomorphed by white mica. Assemblage includes blocky kyanite, possibly after prismatic sillimanite, plus later ﬁ brolitic sillimanite. (A) Plane-polarized light. (B) Cross-polarized light. Scale bar is 1 mm. Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 235

Directions to Stop 3. Depart Stop 2 and continue In addition, John M. Parker III (early 1960s?) wrote a short ~0.8 miles north on Russell Union Road (CR 1206) to the description of the zone entitled “Siliceous Belt north of Drewry” T-intersection with Burchette Road (CR 1218). Turn right in one of a series of blue pamphlets that were county-based geo- (north) and follow Burchette Road (CR 1218) 2.0 miles to logic fi eld guides for schoolteachers. Although Parker did not where it ends at Drewry–Virginia Line Road (CR 1200). Turn mention a fault, he did trace a silicifi ed zone for ~3.2 km near left (southwest) and drive ~1.0 mile on Drewry–Virginia Line the community of Drewry, North Carolina, located ~6.4 km Road (CR 1200) to Kimball Point Road (CR 1204) and turn south of Rose Hill. In the Kerr Dam and northern Middleburg right (west). Travel 0.9 miles to Boulder Boulevard. Turn right 1:24K Quadrangles, there are at least fi ve of these northeast- (north) and park at the end of Boulder Boulevard. Walk due striking silicifi ed cataclasite zones (Buford et al., 2007; Blake north to the lakeshore and proceed west along the shoreline et al., 2010). to the rocky bluff outcrops on the point at Stop 3 [latitude There are at least two approximately east-west–oriented 36.53833°, longitude −78.30834°]. silicifi ed cataclasite zones connected to the informal Rose Hill fault, and Stop 4 highlights the northern zone that trends along Stop 3. Late Paleozoic-Mesozoic(?) Brittle Deformation, the north-facing shoreline of Kimball Point. The second, southern Kimball Point, Kerr Lake State Recreation Area zone trends N80°E ~0.4 km northeast of the Rose Hill commu- Location: Kimball Point Road and north-facing Kerr Lake shore- nity within eastern coves of Dix Branch on Kerr Lake. Together, line just south of the North Carolina–Virginia state line. these three silicifi ed cataclasite zones are informally referred to Map: John H. Kerr Dam 1:24K Quadrangle. as the Rose Hill fault system. Rounding the shoreline to Stop 3, the north-facing ridgeline A common theme along the length of the Nutbush Creek– contains a wave-cut terrace of cobble and boulder debris, as well Lake Gordon fault system in North Carolina is the occurrence of as outcrops of vuggy quartz-epidote rock and silicifi ed cataclasite silicifi ed, and locally epidotized, cataclastic fault zones that are (Fig. 8B). Many chips and fl at rock pieces at the east end of the oriented subparallel or highly oblique to the regional metamor- outcrop are white mica biotite schist, which commonly occurs phic/mylonitic structural grain. These zones range from isolated, regionally as cm- to km-scale enclaves in the granitic mylonitic resistant linear outcrops to more complex networks of intercon- gneiss. Shoreline exposures west of the cataclasite are primar- nected, lattice-like faults that may be several m to km in length ily K-feldspar porphyroclastic, biotite-poor mylonitic granitic and have moderate to steep dips (e.g., Heller et al., 1998; Stod- gneiss. In between these two localities, in-place gneiss is cut by dard et al., 2002). cm-thick quartz veins and is highly epidotized, but continues This stop provides the opportunity to observe multiple ori- to preserve the mylonitic foliation (Fig. 8C). Along the terrace, entations of silicifi ed cataclasite that overprint regional mylonitic angularity of the debris is attributed to the highly fractured char- rocks (Fig. 3). Here, the surrounding rocks are part of a unit acter of the outcrops. informally called Pg1 that is a leucocratic (CI < 10–15), pink- Several obvious fault clasts of epidotized granite, contain- tan and white-gray-tan, dominantly fi ne- to medium-crystalline, ing relic lumps of K-feldspar and foliation and cut by quartz well foliated and lineated, biotite white mica granitic mylonitic veins, are apparent in some block outcrops. In addition to the gneiss. It is part of the suite of mylonitic granitoid gneisses that extreme fracturing, quartz-fi lled vugs in which crystals display occupy the space between fault zones of the Nutbush Creek– rhombohedral terminations stand out in some outcrops. Pre- Lake Gordon fault system and are likely Pennsylvanian-Permian liminary lineation measurements on crystal orientation in the in age and emplaced during the Alleghanian orogeny. In the hill- vugs show they are subparallel to the regional subhorizontal sides and shoreline at this stop, most of the mylonitic gneiss is stretch lineation in granitic mylonitic gneiss. At least one out- exposed as saprolite and the topographic relief is caused by the crop of quartz-fi lled vugs in silicifi ed cataclasite in the north- more resistant silicifi ed cataclasite. ern Middleburg 1:24K Quadrangle displays similar crystal- Oriented parallel to Boulder Road, a dominant ridge-like orientation relationships. boulder fi eld and outcrop fi n of silicifi ed cataclasite strikes While the origin of these silicifi ed cataclasite zones of N15°E, and contains readily apparent fractures striking the Rose Hill fault system is not yet clear, they are common N20°E and dipping 80°NW (200,80) (Fig. 8A). This fi n and structural features in the Nutbush Creek–Lake Gordon fault boulder ridge has been mapped from the community of Keats, system within and along the fault zone boundaries of indi- Virginia, at the North Carolina–Virginia line (located ~0.8 km vidual terranes. Multiple pulses of extension and dilational directly north of Stop 4) to the community of Rose Hill, North opening of fractures develop multiple east-west–oriented, Carolina, ~2.4 km south of Stop 4. It likely continues fur- cataclastic and silicifi ed zones (Fig. 8D). This north-south ther south as indicated by the shaded relief map derived from stretch component tends to be approximately parallel to the LiDAR digital elevation model for Warren County and by the regional, fi nite stretch component preserved as mineral lin- reconnaissance mapping of Bob Butler and Bob Druhan who eation and boudin structure in the mylonitic gneisses and coined the term “Rose Hill fault” (Bob Druhan, personal com- schist enclaves and compositional layering, leading to their mun., 2010). east-west orientation. Extension and dilational opening of 236 Blake et al.

fractures leading to the north-south–oriented silicifi ed zones Stop 4. Mylonitic Alleghanian(?) Granitoids and is roughly orthogonal to this stretch component and parallel Gneissic Enclaves, County Line Park, Kerr Lake to the regional foliation. Where locally preserved, slickenline State Recreation Area and vein fi ber orientations suggest down-dip displacement Location: Dix Creek, County Line Park Picnic Area, and its west- on the north-south zones. Similar zones of silicifi ed and epi- and north-facing Kerr Lake shorelines. dotized cataclasite defi ne the locations and trends of normal Map: John H. Kerr Dam 1:24K Quadrangle. faults related to rift development along the eastern margin of the Triassic Deep River rift basin including the bounding When the lake level is at or below normal, this stop pro- Jonesboro fault and FCFZ. vides spectacular views of ductile dextral strain of the Nutbush Directions to Stop 4. Depart Stop 3 and return ~0.9 miles Creek–Lake Gordon fault system. The rocks here were origi- on Kimball Point Road to Drewry–Virginia Line Road. Turn nally mapped as Neoproterozoic to Cambrian inequigranular right (south) and continue 2.2 miles to Buchanan Road (CR and megacrystic garnet-bearing biotite gneiss, interlayered with 1202). Turn right (west) and proceed 0.7 miles to County Line and gradational into mica schist and amphibolite, and containing Road. Turn right (north), travel 1.2 miles, and turn right (east) small masses of granitic rocks (NCGS, 1985). Butler and Druhan onto County Line Park Road at the T-intersection. Proceed (unpublished mapping) traversed the lakeshore and adjacent 1.1 miles to the end of the loop road. Walk to shoreline and series streams in both the Virginia and North Carolina portions of Kerr of lake level-dependent outcrops at Stop 4 [latitude 36.53232°, Dam 1:24K Quadrangle and mapped the point as layered gneiss longitude −78.3197°]. and schist of the Raleigh terrane. The notes on their fi eld sheets

Figure 8. Outcrop features at Stop 3. (A) Prominent ridge-like boulder fi eld and outcrop fi n of silicifi ed cataclasite that regionally trends N15°E and marks the position of the informally named Rose Hill fault. View south. (B) East-west– trending zone of silicifi ed cataclasite, vuggy quartz veins, local epidosite, and epidotized granitic gneiss mylonite that extends ~0.25 km west of this stop. View east. Hammer is 34 cm in length for scale. (C) Close-up of epidotized granitic mylonite gneiss enclaves in silicifi ed cataclasite that preserve a relic high-strain foliation and crosscutting, vuggy quartz veins. Pen is 11 cm in length for scale. (D) Multiple generations of fractures develop scale-variable, east-west–oriented cataclastic and silicifi ed zones. Hammer is 34 cm in length for scale. Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 237

describe biotite gneiss, granitic gneiss, amphibolite, and other the pre- or syn-kinematic magmatic phase. In some cases, the compositional layering. increase in schist enclave abundance seems to locally correspond Horton et al. (1993a) remapped the area, classifying County with some increase in biotite content of the granitic gneiss, per- Line Park Point as part of a unit of granitic gneiss lying south of haps suggestive of enclave digestion and biotite enrichment of the the Late Pennsylvanian Buggs Island granite. On their map, the granitic magma, but no clearcut relationships are yet recognized. unit constitutes a large Alleghanian orogeny granitic gneiss that In other compositional layers that also may be large enclaves is ﬂ anked by the Nutbush Creek fault zone to the west and the in granitic gneiss, hornblende ± biotite ± epidote ± retrograde Lake Gordon fault zone to the east in the south-central Virginia chlorite and plagioclase dominate the mineral assemblage of Piedmont (Horton et al., 1993a; Butler and Horton, 1995; Sacks, amphibolite, especially at the western point of the park (Fig. 9A). 1999; Virginia Division of Mineral Resources [VDMR], 1993). These layers, ranging from cm to m in width and length may con-

We have mapped these outcrops as part of the informal Pg1 sist entirely of melanocratic and leucocratic compositional layers unit, which is primarily foliated granitic mylonitic gneiss (Fig. that form internally coherent gneiss layers bounded by granitic 9). The unit as a whole tends to be leucocratic (CI < 10–15), pink- gneiss. Several large domains dominated by amphibolite rather tan and white-gray-tan, dominantly ﬁ ne- to medium-crystalline, than granitic gneiss are inferred to extend across to Kimball well foliated and lineated, white mica ± biotite granitic gneiss. Point, another amphibolite-rich locality in this unit. However, some domains vary in biotite and white mica content Other amphibolite layers have pegmatitic granitic gneiss (CI up to 25–35). These phyllosilicates join pink-white micro- seams intruded along strike of the foliation or are separated and cline, plagioclase, and quartz in the mineral assemblage. bounded by pegmatitic granitic gneiss into separate amphibolite Locally, biotite-white mica schist, which may contain ﬁ bro- layers; in each case, the granitic gneiss appears to be a later sill-like litic sillimanite, and thin felsic gneiss layers form compositional injection (Fig. 9B). In several places, these amphibolite and dioritic layering oriented parallel to the mylonitic foliation in granitic gneiss assemblages are reminiscent of Raleigh Gneiss exposures gneiss. These rocks appear to be enclaves incorporated into farther south in the Henderson and Raleigh 100K sheets.

Figure 9. Outcrop features at Stop 4. Pen is 11 cm in length for all views. Shear sense is tops-north to the right in Figures A–E. (A) Centimeter-to- meter-scale compositional layering, and pinch-and-swell and tension gash structures preserved within amphibolite that is encased by biotite-poor and biotite-rich granitic gneiss mylonite. (B) Sigma-type boudin structure and K-feldspar winged porphyroclasts of amphibolite and pegmatitic granitic mylonite gneiss displaying consistent tops-north, dextral asymmetry in the steeply west-dipping mylonitic foliation. (C) C–C′ shear band relationships developed in amphibolite layering between two phases of porphyroclastic K-feldspar biotite granitic gneiss mylonite. (D) Rootless isoclinals fold preserved in biotite granitic gneiss that is crosscut by biotite-poor granitic gneiss mylonite. (E) Truncation of biotite-rich granitic gneiss mylonite foliation by highly foliated granitic gneiss mylonite shows the progressive ductile strain history in Nutbush Creek–Lake Gordon fault system. (F) Mesoscale siliciﬁ ed fault zone oriented slightly oblique to granitic gneiss mylonite foliation that displays dip-slip fault polish and normal sense of slip of brittle fault. View to east. 238 Blake et al.

Compositional layers are variably stretched in the dominant different pluton (perhaps even an extension of the Buggs Island) plane of mylonitic foliation, commonly forming pinch and swell remains to be determined through detailed mapping. structure while others terminate as elongate asymmetric boudins, Directions to Stop 5. Depart Stop 4 and return to the especially in amphibolite as noted by Butler and Druhan (unpub- T-intersection between County Line Park Road and County Line lished mapping). Boudin stretch directions are coincident with Road. Turn right (west) onto County Line Road. Proceed 0.6 miles the dominant northeast-trending subhorizontal mineral lineation, and park along the road. Walk north to the rocky Kerr Lake shore- making it a stretching lineation. Due to compositional strain par- line and Stop 5 [latitude 36.52248°, longitude −78.3301°]. titioning, other layers form scale-variable sets of asymmetric fi sh- like structures. Steeply dipping fi ns of foliation also display this Stop 5. Jurassic “Devil’s Backbone” Diabase, County Line top-north asymmetric sweep. These features allow S- surfaces, Park, Kerr Lake State Recreation Area and C- and C′-shear surfaces to be readily identifi ed and mea- Location: Western portion of County Line Park and east-facing sured (Fig. 9C). Also, sigma-type winged K-feldspar porphyro- Kerr Lake shoreline. clasts are fl attened and rotated and contribute to the composite Map: John H. Kerr Dam 1:24K Quadrangle. S-C surfaces and C–C′ surfaces. Finally, in still other layers, varieties of granitic gneiss Assuming the lake is not too high, here we see an extensive produce the compositional variations. In addition to changes linear boulder fi eld along the lakeshore exposing a coarse-crys- in white mica ± biotite content, these layers may vary in talline, two-pyroxene, granophyre- and locally quartz-bearing (1) original magmatic crystal sizes, (2) degree of penetration of diabase, texturally and mineralogically distinct from the more strain that also leads to changes in bulk crystal sizes and forma- common olivine diabase. This dike has been mapped from cen- tion of rootless isoclinal fold hinges (Fig. 9D), (3) quantity and tral Johnston County north for a distance greater than 120 km, size of K-feldspar porphyroclast development, (4) number of crossing the state line into Virginia. In the southern part of its thin, cm-scale mesocratic versus leucocratic mineral domains outcrop area near Flowers, North Carolina, the dike trends about that appear to represent relic wallrock(?) layering versus leu- N15°W, curving to a N-S direction near Rolesville, and then to cocratic dike and sill injections of later intrusive granitoid, and approximately N10°E north of Henderson. The dike appears to fi nally, (5) amount of white- to white-pink and red-pink pegma- be between 32 and 40 m in width. Field evidence and magnetic titic granite and granitic gneiss injections, again as either dikes modeling suggests that it dips eastward 75–80° near Middleburg. or sills. While these relationships are apparent at County Line This dike is particularly well exposed due to large semi- Park, in outcrops to the north at Kimball Point and the point continuous bouldery outcrops (Fig. 10A), including a number west of Keats, Virginia, pegmatitic granitic gneiss dominates of spots where a stream crosses it, and the entire width of the the granitic gneiss, forming m-high, and m-scale elongate fi ns dike may be sampled. There is also a close relationship to geo- that preserve multiple and consistent dextral sigma-type por- morphology, with the dike trending parallel to stream courses in phyroclast relationships. some cases, and in others the dike trends along ridge-tops. In the In fact, the predominance of dextral kinematic indicators sig- Kittrell 1:24K Quadrangle, just north of the Tar River, an elderly nifi cantly contributes to the overall strain character and grain of man told one of us all about the dike without knowing any geol- these outcrops and the granitic gneiss unit as a whole. Overprint ogy. He said he reckoned you could walk on those boulders all of protomylonitic, mylonitic and ultramylonitic fabric elements the way up to Henderson, and he even knew where the dike obscures many contact relationships. Highly transposed, subpar- crosses several roads on the way. He said “Folks around here call allel granitic mineral assemblages and foliation appear to have that ‘The Devils Backbone’.” developed during pre-full magmatic crystallization and crystal- Where mapped, the dike intrudes granitoid country rocks plastic deformation. Truncation of foliation by other highly foli- of the Rolesville batholith and older metamorphic rocks of the ated granitoids highlights the progressive strain history in this Spring Hope and newly defi ned Warren terranes. The dike also fault system (Fig. 9E). intrudes rocks that have been ductilely deformed within the Nut- The abundance of planar C-C′ relationships combined with bush Creek–Lake Gordon fault system, but the diabase shows silicifi ed fractures oriented both subparallel and highly oblique to no evidence of ductile deformation. In several places, the dike S-C foliation (Fig. 9F) suggests that these outcrops experienced is transected by brittle faults at a high angle, and at one loca- extension similar to Stop 3. Because of their along-strike position in the southwestern Middleburg 1:24K Quadrangle, the tion in the Nutbush Creek–Lake Gordon fault system, these rocks dike is clearly cut and offset along a north-dipping normal fault. may be the high strain equivalent of granitoid rocks at optional Petrographic characteristics include a generally coarser crystal Stop 8 lying within this large area of granitoid injections into size than most olivine diabase and a low-Ca pyroxene in addi- fault zones. Again, we interpret this mixing of granite textures tion to an augitic, high-Ca pyroxene (Fig. 10B). Plagioclase and fabric elements to indicate that magma intruded repeatedly occurs commonly as rectangular laths, but also locally as large in pulses, during and following the time of shear strain displace- blocky phenocrysts (Fig. 10C). The diabase locally contains a ments. Whether this northwestern region of the “Rolesville fi ne granophyric intergrowth of alkali feldspar and quartz (Fig. batholith” really belongs to that intrusive phase, or constitutes a 10D). The two-pyroxene diabase is quartz normative and shows Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 239

many other indications of being somewhat more evolved than the Stop 6. Deformed Pennsylvanian Granitoids, more common olivine diabase variety. Silica, Ti, alkali elements, Lake Gordon Shear Zone Rb, Zr, Th, and U are higher in the quartz-normative dike than in Location: Top wall of stone quarry 1.1 km northwest of E.O. olivine diabase, while Mg and transition metal elements are in Young Elementary School in Middleburg. lower concentrations than in olivine diabase. Map: Middleburg 1:24K Quadrangle. Directions to Stop 6. Depart stop and return to the T- intersection between County Line Park Road and County Line Here we visit an excellent exposure in an abandoned quarry Road. Turn right (south) onto County Line Road and drive 1.2 miles of strongly deformed protomylonitic to mylonitic granitic rock to Buchanan Road (CR 1202). Turn left (east), driving 0.7 miles (Fig. 3) referred to as Middleburg gneiss by Parker (undated, back to Drewry–Virginia Line Road (CR 1200), which to the south likely early 1960s). This is one of several small inactive quar- is called Jacksontown Road (CR 1369). Turn right (south) and ries in the vicinity of Middleburg (Ronald Stainback, personal travel 6.8 miles to the T-intersection with Jackson-Royster Road commun., 2011); most of them are now backﬁ lled. Known as the (CR 1400). Turn right (west) on Jackson-Royster Road and pro- Carroll Quarry, it produced dimension stone as long ago as 1899 ceed 1.2 miles to Flemingtown Road (CR 1371). Turn left (south) that was used for curbing and blocks in Norfolk and Portsmouth, and proceed 0.9 miles to East Spain–Middleburg Road. Turn left Virginia (Watson and Laney, 1906). The quarry may have also (east) and drive 0.3 miles to the sharp bend in the road and park. been used during construction of I-85. Walk south across the stream, uphill, and into the woods ~0.1 mile The rock is medium-crystalline porphyroclastic biotite to Stop 6 [latitude 36.40243°, longitude −78.33972°]. granite with a color index of ~10. The rock is less gneissic than

Figure 10. Outcrop features at Stop 5. (A) Lakeshore boulder ﬁ eld exposure of diabase dike looking south along strike. Trains of such boulders gives this dike the local nickname “Devil’s Backbone.” Figures B–D show some petrographic features from dike samples in the Henderson 1:24K Quadrangle. (B) Photomicrograph under crossed polars, showing relatively coarse crystal size and texture of a sample of two-pyroxene diabase. (C) Large plagioclase phenocrysts are

commonly strongly zoned, with the core very calcic at An90 (anorthite) and the rim in the An50–70 (labradorite) range. Cross-polarized light. (D) A granophyric intergrowth of alkali feldspar and quartz is another diagnostic feature of this diabase. Cross-polarized light. Scale bars are 1 mm and 0.5 mm, respectively. 240 Blake et al.

many granitoids to the east, and overall appears relatively homo- a steeply east-dipping foliation, and a late brittle fault trending geneous and more penetratively deformed (Figs. 11A, 11B). It approximately east-west cuts the granitic rocks. carries a strong biotite foliation, fl attened and locally ribboned At the latitude of Middleburg, a large region (“sea”) of feldspars; these foliations are near-vertical and strike N10°E to granitic rocks, most very strongly deformed, lies within the N15°E. Rare winged porphyroclasts and a stretch lineation indi- Nutbush Creek–Lake Gordon fault system, from the edge of cate subhorizontal dextral shear strain. We map this exposure the Carolina terrane on the west, to the edge of the Warren ter- near an unnamed fault zone. rane on the east. Modest petrographic differences have led us to A thin section shows alkali feldspar porphyroclasts having divide them into three parallel map-units, but the distinctions cores of relic Carlsbad-twinned perthitic orthoclase mantled by are not major. In the John H. Kerr Dam 1:24K Quadrangle, fi ner microcline derived from the outer portions of the original Horton et al. (1993a) mapped a pre-Alleghanian granitic gneiss phenocrysts (Fig. 11C). With Q:A:P of ~30:60:10, this rock unit between the two mylonite zones, whereas we map granitic is a syenogranite using the IUGS classifi cation. In addition to rocks, presumably late Paleozoic, in the same area, on strike the aligned dark brown biotite, the rock contains signifi cant and to the south of where Horton et al. (1993a) showed the unoriented post-kinematic white mica. Allanite is a distinctive Buggs Island pluton ending. Furthermore, we see no defi nite accessory phase present in this granite; it has also been found break in the deformation fabric elements across this zone of in deformed granite at the western edge of the Vicksboro 1:24K granitoids. Whether the granite located at Stop 6 belongs to the Quadrangle, ~10 km to the south and approximately along composite Rolesville batholith, Buggs Island pluton, or neither, strike. Between these two locations, in the northwest corner of remains to be seen. Continued mapping, petrographic analysis, the Vicksboro 1:24K Quadrangle, the Greystone Quarry, oper- geochemical, and geochronological study will be necessary to ated by Vulcan Materials, exposes protomylonitic to mylonitic make that determination. granite, leucogranite, and pegmatite, with some gneissic variet- Directions to Stop 7. Depart Stop 6 and return to Fleming- ies and enclaves and selvages of biotite gneiss. Foliation defi ned town Road (CR 1371) and turn right (north). Proceed 1.0 mile by oriented biotite and by gneissic layering is variable but aver- and turn left (west) on Anderson Creek Road (CR 1374). ages nearly north-south; there is also a subhorizontal mineral Travel 1.7 miles to the T-intersection with Satterwhite Point stretching lineation. Also at the quarry, late chlorite fi lms defi ne Road (CR 1319). Turn left (south) and proceed ~1.4 miles to

Figure 11. Outcrop and petrographic features at Stop 6. Shear sense is tops-north to the right in Figures A and B. (A) Outcrop showing granitoid mylonite. Rock is a biotite syenogranite with prominent alkali feldspar porphyroclasts deformed into ribbons. Surface is nearly horizontal, top of the photo is toward the west. (B) Another area of Stop 6 exposure showing large winged feldspar porphyroclast indicating dextral shear. Top of photo is to the west; hammer is 32 cm long. (C) Photomicrograph from outcrop at Stop 6. Porphyroclasts have Carlsbad- twinned perthitic orthoclase in their cores, mantled by recrystallized matrix containing microcline. Rock contains Q:A:P of ~30:60:10, 8% biotite, 5% white mica, and carries signiﬁ cant allanite as the main accessory mineral. Cross-polarized light. Scale bar is 1 mm. Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 241

Nutbush Road (CR 1308). Turn right (west) and drive 3.0 miles leucocratic dikes and larger intrusive porphyritic quartz tonalite to its intersection with NC 39. Turn right (north) and proceed (CI < 5) stocks as observed at the point just west of the boat ramp 9.3 miles to the Y-intersection with Rock Spring Church Road (Figs. 12A, 12B). The Vance County pluton also preserves xeno- (SR 1356). Bear to the right and drive 3 miles to Reverend Hen- liths of both mesocratic and leucocratic plutonic and volcanic derson Road. Turn right (east) and proceed 1.5 miles into Hen- rocks, which in a high-strain state contribute to the white mica derson Point Park and take the fi rst left (north) inside the park. phyllonite and crystalline and cryptocrystalline felsic mylonite This road leads to a boat ramp on the west side of Kerr Lake, and ultramylonite structures at this point. 0.3 miles past the left turn. Walk east to the western shoreline We also map this point as part of a signifi cant zone of green- of Nutbush Creek, Kerr Lake and Stop 7 [latitude 36.5371°, schist facies phyllonite and mylonite that corresponds with the longitude −78.34171°]. eastern boundary of the northern Carolina terrane in the north- central North Carolina Piedmont. It extends from the state line Stop 7. Phyllonite and Mylonite of the Carolina Terrane, south to Satterwhite Point State Recreation Area on Kerr Lake Nutbush Creek Fault Zone, Henderson Point Park, in the Middleburg 1:24K Quadrangle. South of that point, the Kerr Lake State Recreation Area phyllonite becomes a less prominent rock type in the Towns- Location: East-facing shoreline of Nutbush Creek and Kerr Lake ville 1:24K Quadrangle in favor of felsic mylonite from the from a point just west of the boat ramp around to the northern north-central portion of the Henderson 1:24K Quadrangle to the point of the park. Wilton 1:24K Quadrangle where it is truncated by the Triassic Map: John H. Kerr Dam 1:24K Quadrangle. Jonesboro fault. The rocks at Henderson Point display scale-variable dextral When the lake is at or below normal levels, this stop pro- planar and linear kinematic indicators that are characteristic of vides spectacular views of ductile dextral strain of the Nutbush this high-strain zone. Planar indicators range from mm to m in Creek–Lake Gordon fault system. The rocks here were originally length, width, and height in a heterogeneous mix of highly trans- recognized by Parker (1963, 1968, 1978) as a unique strip of posed, rotated, and attenuated, northeast-striking and steeply phyllite along the eastern boundary of the Vance County pluton, west-dipping compositional layers. Layering produces a scale- a tonalite to granodiorite pluton in the Carolina terrane (Fig. 3). variable, ductile fl uxion structure as originally described by Casadevall (1977) reinterpreted the phyllite as fault zone phyl- Druhan et al. (1994). Phyllonite “fi ns” are predominantly a mix- lonite and mylonite, noting the correlation between a regional ture of phyllosilicate minerals and quartz that vary in their ratio of northeast-southwest-oriented, linear aeromagnetic anomaly and chlorite to white mica. This change leads to medium green-gray the topographic lineament produced by Nutbush Creek along mesocratic and silver-gray leucocratic, laminated color variations Kerr Lake Recreation Area. in outcrop (Figs. 12C, 12D). Fractures, some silicifi ed, overprint Subsequently, these rocks were described as a linear-tending most outcrops, having orientations that are either subparallel with zone of Neoproterozoic to Cambrian phyllite and schist con- or highly oblique to layering and regional high strain foliation taining minor biotite and pyrite, and noted for being associated (Fig. 12C). with fault zone phyllonite and sheared metasedimentary and In more chlorite-rich layers, chemical weathering may be metavolcanic rocks (NCGS, 1985). Butler and Druhan (unpub- so extreme that asymmetric Fe-oxide and Fe-hydroxide saprolite lished mapping) also noted the spectacular structures at this stop, layers highlight the phacoidal-shaped disks (fi sh structures) in while Druhan (1983) and Druhan et al. (1994) carefully mapped white mica-rich layers. Some composite white mica fi sh struc- this phyllonite/mylonite zone and then a zone of regionally high tures are 0.5–1 m in length and litter the beaches as phacoid- strain from the North Carolina–Virginia state line southward. shaped disks. Other compositional layers contain phacoidal They provided a regional synopsis of the structural character and “schools” of cm-scale chlorite fi sh structures that are consis- regional extent of the ductile dextral Nutbush Creek fault zone, tently displaced in a tops-north, dextral asymmetry as S-C–style, now a strand within the Nutbush Creek–Lake Gordon fault sys- reverse-sense crenulations between more leucocratic ledges. tem, along the western fl ank of the Wake-Warren anticlinorium Centimeter-scale quartz ribbons display similar asymmetric in the North Carolina eastern Piedmont. geometries interspersed within the phyllosilicate fi sh. Normal- The compositional origin of these high strain layers is not sense crenulations also bound smaller-scale schools of fi sh struc- clear. As suggested by Druhan et al. (1994) and clearly mapped in tures, and in some exposures join as cm- to m-scale C–C′ shear the Kerr Dam and Middleburg 1:24K Quadrangles, some layer- band surfaces that are synthetic to the overall dextral shear sense ing represents highly deformed portions of the greenschist facies of this phyllonite zone. Vance County pluton of Neoproterozoic age (LeHuray, 1989; In contrast, fi ne-crystalline leucocratic phyllonite, mylonite, Druhan et al., 1994). The pluton is a metamorphosed medium- to or ultramylonite are composed of a mixture of quartz and feldspar coarse-crystalline granodiorite and tonalite (CI ~45), which in and variable amounts of white mica. These felsic ultramylonitic a high-strain state contributes to the production of many of the zones will form individual cryptocrystalline compositional layers white mica + chlorite phyllonite exposures. It also displays mul- in the phyllonite fl uxion structure, and larger domains of highly tiple crosscutting phases of mesocratic, leucocratic, and holo- foliated, composite S-C fabric elements. Their higher competence 242 Blake et al.

Figure 12. Outcrop features from Stop 7 at Henderson Point. (A) Boulders of unfoliated blue quartz hornblende biotite tonalite from the Vance County pluton in the Carolina terrane. Outcrop west of the Nutbush Creek fault zone in the western portions of Henderson Point along Kerr Lake. MacIntyre(†) and Cutler are 75 cm in length for scale. (B) Highly foliated, fractured and silicifi ed leucocratic tonalite-granodiorite of the Vance County pluton at the eastern boundary of the Carolina terrane along the western edge of the Nutbush Creek fault zone. Outcrop demonstrates the ductile-brittle deformation character of the western boundary of the Nutbush Creek fault zone. Hammer is 28 cm in length for scale. (C, D) Composite tops-north S-C surfaces in foliated leucocratic tonalite-granodiorite of the Vance County pluton at the western boundary of the Nutbush Creek fault zone and Nutbush Creek–Lake Gordon fault system. Schools of cm-scale felsic white mica phacoids (fi sh structures) in phyllonite all consistently displaced in a tops-north, dextral asymmetry as S-C–style planar fabric elements. View down and west in (C) and (D). Pen is 11 cm in length for scale. also allows them commonly to be disharmonically and tightly to left (west) at the next light in front of Maria Parham Medical isoclinally folded, having hinges that may plunge steeply down Center. Bear left (west and south) past the center and proceed dip, or moderately and shallowly to the northeast in accordance 0.1 miles onto the I-85 service road known as Market Street and with the subhorizontal to moderate northeast-plunging mineral then into the Sleep Inn parking lot at 18 Market Street, Hender- lineation. In numerous exposures along this zone, cm- to m-scale son, North Carolina. asymmetric isoclinal folds have highly attenuated and/or thrust- Directions to Optional Stop 8. Depart Henderson Point Park faulted eastern limbs leading consistently to tops-north hanging and return to NC 39. Turn left (south) and travel 13.5 miles to wall displacements. In other exposures, felsic layers form asym- the I-85 interchange. Proceed 2.1 miles through Henderson on metric, competent boudins in a more phyllonitic matrix, stretched NC 39 (Andrews Ave) to the interchange with U.S. 1 Bypass subparallel to the dominant mineral lineation. South. Turn right (south) onto U.S. 1 and merge onto the south- End of Day 1. Depart Henderson Point Park and return to bound bypass. Drive 4.5 miles to Cobble Way in the Cobble- NC 39. Turn left (south) and proceed 13.5 miles to Hender- stone subdivision. Turn left at Cobble Way, then take a left at the son, North Carolina, and the I-85 South interchange. Turn left T-intersection onto North Cobble Creek Drive, then a right onto (north) and downhill onto the curved on-ramp and drive 2 miles Stonehedge Drive. Proceed to the end of the cul-de-sac straight south to Exit 212 at Ruin Creek Road. Turn right (north) at the ahead. Park and walk to the pavement exposure. Stop 8 [latitude traffi c light at the top of the off-ramp and then turn immediately 36.26334°, longitude −78.4142°]. Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 243

Stop 8. Late Paleozoic Granitoids on the Western Flank of even an extension of the Buggs Island) remains to be seen. At the Wake-Warren Anticlinorium previous stops, we examined the equivalents of these granitic Location: Cobblestone subdivision, located in southeast Hen- rocks having different and higher degrees of shear strain. derson between U.S. Highway 1 Business and U.S. Highway 1 Directions to the Sleep Inn from Optional Stop 8. Return to Bypass, ~0.5 km west of Gill, North Carolina. U.S. 1 and turn right (north). Proceed 0.6 miles to the off-ramp Map: Henderson 1:24K Quadrangle. to U.S. 1 Business (Raleigh Road). Turn left (north) on U.S. 1 and proceed 2 miles to the T-intersection with Belmont Drive/ As portrayed on the State Geologic Map of North Carolina Old Country Home Road and turn left (west). Drive 1.4 miles to (NCGS, 1985), the Rolesville batholith extends for some 100 km the new traffi c light at the T-intersection with the new Dr. Martin along the generally north-south trend of the Wake-Warren anti- Luther King, Jr. Bypass. Turn right (north) and continue 3.6 miles clinorium, and for 20–30 km across that trend. The batholith to the Ruin Creek I-85 exit. Cross over the interstate and turn left actually consists of a number of mutually intrusive individual at the light in front of Maria Parham Medical Center. Bear left plutons that may be distinguished, with some diffi culty, on the (west and south) past the center and proceed 0.1 miles onto the basis of texture, mineralogy, and enclave characteristics (Speer, I-85 service road known as Market Street and then into the Sleep 1994). Some other named late Paleozoic intrusive granitic bod- Inn parking lot at 18 Market Street, Henderson, North Carolina. ies in the region are in contact with the Rolesville (e.g., Castalia and Gupton) and may belong to the batholith; other bodies (e.g., DAY 2. HENDERSON TO THE DEEP RIVER TRIASSIC Wise, Wyatt, Lake Benson) are separated from the batholith by BASIN AND THEN CHARLOTTE metamorphic country rocks. Mapping along the northwestern margin of the batholith Directions to Stop 9. Depart the Sleep Inn and proceed to has shown that much of the granitic rock is deformed, and some the on-ramp for I-85 South. Drive 6 miles south to Exit 206 and of it is strongly deformed (Fig. 3). Whereas much of the granite merge right at the top of the off-ramp onto U.S. 158 West. Travel mapped in the Louisburg 1:24K Quadrangle, near the heart of the 0.5 miles and turn right (west) at the traffi c light onto U.S. 158 batholith, is equigranular to very slightly feldspar-phyric (either Bypass and drive past the Revlon factory ~0.7 miles just across alkali feldspar or plagioclase may be the phenocryst phase), gran- the crest of this broad hill. Park on the right (north) side of the itoid rocks to the west and northwest tend to be gneissic, and road, cross, and walk south into the woods to Stop 9 [latitude locally protomylonitic to mylonitic. Toward the west and south 36.32174°, longitude −78.55862°]. of Henderson, gneissic varieties of granite gradually merge with Raleigh Gneiss of the Raleigh terrane. Stop 9. Ductile Mylonite Gneiss and Brittle Silicifi ed The state geologic map shows the northern termination of Cataclasite in Metagranite, Fishing Creek Fault Zone the Rolesville batholith in the center of the Middleburg 1:24K (a.k.a. The Revlon Outcrop), Oxford, North Carolina Quadrangle, with a large tract of biotite gneiss and schist extend- Location: Small ravine tributary to Coon Creek on its west-facing ing to the Virginia line (NCGS, 1985). Mapping in Virginia (Hor- fl oodplain bluffs just north of the Revlon factory. ton et al., 1993a; VDMR, 1993) depicts the southern termination Map: Oxford 1:24K Quadrangle. of the late Paleozoic Buggs Island pluton just north of the border. Where these maps show metamorphic country rock between One of the major tectonic events affecting the Carolina Zone these large plutons, we have instead mapped mainly strongly involves early Mesozoic rifting of the Pangean supercontinent deformed granitoid rocks, locally containing sizable country rock (Olsen et al., 1991; Stoddard et al., 1991; Hibbard et al., 2002). enclaves. We ascribe much of the strain fabric in these rocks to The formation of the Triassic Deep River rift basin between the effects of the Nutbush Creek–Lake Gordon fault system. the eastern and central Piedmont records this episode of crustal Here at Stop 8 we see an exposure of granite that displays extension and continental breakup (Clark et al., 2001, 2011). Its an older, locally protomylonitic foliation, showing the effects of development and the petrology of bounding crystalline rocks and major fl attening and sparse indications of dextral shear. Subpar- basin sedimentary rocks are the focus of the second day of the allel to this major fabric, which strikes about N10°E, are sills fi eld trip. and dikes of weakly to strongly foliated granite that lack strong From south to north, the Wadesboro, Sanford, and Durham evidence of mylonitization. Still other portions of this outcrop, sub-basins are formal subdivisions of this irregularly shaped, and nearby roadcuts on the U.S. Highway 1 Bypass, are appar- half-graben rift basin (Figs. 2, 4, and 5). The ductile-brittle Jones- ently undeformed, exhibiting equigranular, medium- to coarse- boro normal fault forms the eastern boundary of the Wadesboro, crystalline textures. Figures 13A–13C shows some of these fea- Sanford, and southern portion of the Durham sub-basins (Olsen tures in outcrop. We interpret this mixing of granite textures and et al., 1991; Clark et al., 2001, 2011). The Fishing Creek fault fabric elements to indicate that magma intruded repeatedly in zone (FCFZ) forms the eastern boundary of the northern Durham pulses, during and following the time of fault motion. Whether sub-basin. These half-graben sub-basins structurally separate the this northwestern region of the “Rolesville” really belongs to the easternmost Carolina terrane consisting of the Cary sequence Rolesville batholith, or constitutes a different pluton (perhaps and its associated metagranitoid plutons in the eastern Piedmont 244 Blake et al. from the Virgilina and Albemarle sequences and their associated ( CZdito). Similar rock compositions, close unit contacts, and metagranitoid plutons in the main portion of the Carolina terrane transitional structural boundaries provide the basis for these in the central Piedmont (Farrar, 1985b; Harris and Glover, 1988; correlations (Hadley, 1973, 1974; Farrar, 1985b; Parnell et al., Blake et al., 2001; Hibbard et al., 2002). 2006b; Parnell, 2012). Historically, the mapped occurrences of Triassic clastic Entering into the woods here, random fl oat blocks of the rocks have been used to mark the areal extent of the Deep River meta-intrusive suite mark the underlying unit. Stocks of gran- rift basin (NCGS, 1985). However, recent mapping by Parnell ite, leucogranite, granodiorite, tonalite, and trondhjemite are the et al. (2006b) and Parnell (2012) indicate that basin-bounding rock types that primarily comprise this heterogeneous lithodeme. ductile-brittle fault structures extend past the northernmost Rock samples range in color from pale pink or tan to light gray mapped occurrences of Triassic sedimentary rocks as the FCFZ and white on fresh surfaces, and yield dark brown to red-brown continues northward. LiDAR data shows a strong topographic colors on weathered surfaces. Compositions range from leuco- lineament along Coon Creek in the central portion of the Oxford cratic (CI = 10–15) to locally hololeucocratic (CI = 5–10). They 1:24K Quadrangle. This lineament supports the mapping data that are phaneritic and medium- to coarse-crystalline. K-feldspar underlying structures control topography and that ductile-brittle phenocrysts locally range up to 10 mm in diameter in granitic phyllonite and cataclasite continue north of the last mapped Tri- compositions. Locally, fi nely crystalline microdiorite enclaves assic clastic sedimentary rock outcrops. are randomly distributed in the plutons As such, the informally named FCFZ forms the structural The foliated equivalent of the intrusive granitoid unit occurs boundary for the north portion of the Durham sub-basin. In the in outcrop just to the north of this stop. It is leucocratic (CI ~ 10), region surrounding this stop, three tectonite units defi ne the pale green and pink to green-gray and consists of chlorite-white FCFZ northward along Coon Creek and into the Stovall 1:24K mica phyllonite and protomylonite. These rock types defi ne the Quadrangle just to the north. From south to north, schist, phyl- FCFZ along Coon Creek. East of the FCFZ, several subparallel lonite, and mylonite ( CZphc), foliated felsic meta-intrusive suite anastomosing shear zones in granite range from approximately ( CZgrf), and foliated chlorite-biotite metagranodiorite ( CZfgd) several m-wide up to a half a km-wide. This unit also includes are interpreted as deformed equivalents of plutonic protoliths of silicifi ed varieties found in and adjacent to domains of brittle granite ( CZg), intrusive granitoid ( CZgr), and diorite-tonalite deformation in and near the FCFZ. It has a pale pink and green,

Figure 13. (A) Medium-crystalline, protomylonitic biotite granite cut by dike of ﬁ ne foliated granite. Pictured surface is horizontal, top of photo is toward the east. Strike of foliation is about N10°E. Hammer is 32 cm long. (B) Close-up view of protomylonitic biotite granite at Stop 8 showing prominent alkali feldspar porphyroclasts showing indication of dextral shear. Pictured surface is horizontal, top of photo is toward the east. (C) Close-up view of a different area of the pavement exposure at Stop 8. This medium-crystalline biotite granite to leucogranite is only weakly foliated, if at all, dem- onstrating that pulses of granitic magma intruded over a period of time, including post-kinematically. Pictured surface is horizontal, top of photo is toward the east. Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 245

to green-gray color on fresh surfaces and a brown-gray color on lonite. These rocks have composite S-C high strain foliations weathered surfaces. Locally, domains of epidotized rock exist in that overprint a relict phaneritic texture. Typically, S-C fabric this unit, forming large boulders and resistant outcrops within the development is more prevalent in phyllonitic portions of the unit FCFZ for much of its length. where abundant chlorite and lesser white mica occur. Alignment Moving down the ravine, large outcrops of silicifi ed rock of white mica, biotite, quartz ribbons, and minor chlorite defi ne are part of a linear ridge of multiply fractured and silicifi ed cata- the dominant gneissic foliation S1C. Plagioclase and K-feldspar clasite defi ning the western margin of the FCFZ. Greenish gray σ-type porphyroclasts display wings of white mica, dynamically to gray-white clasts are very angular, consisting of both silici- recrystallized quartz, and small amounts of plagioclase. These fi ed non-foliated granitoids (Fig. 14A) and foliated phyllonite wings form a monoclinic mortar microstructure that suggests a and protomylonite equivalents of this unit (Fig. 14B) that range tops-down-to-the-west sense of displacement in oriented thin from mm-to-m in diameter. Locally, vuggy xenomorphic to idio- sections (Fig. 14C). morphic quartz occurs in open void spaces between angular rock The west-dipping alignment of chlorite, white mica, and bio- clasts or produces drusy coatings on the cataclastic fragments. tite also defi nes an S1S schistosity oriented oblique to S1C, especially At the bottom of the ravine and in many creek bottoms along adjacent to porphyroclasts of plagioclase and K-feldspar porphy- the FCFZ, there are light green-gray to dark green subvertically roclasts. S1S is not readily observed at the mesoscale; however, at oriented phacoidal folia that protrude up from the creek bottom the microscale, the dominant and more evolved fabric element is in a manner analogous to shark fi ns. These rocks include chlo- the penetrative metamorphic mineral foliation, S1C, which over- rite schist, chlorite white mica phyllonite, and felsic protomy- prints the S1S foliation and defl ects it into a tops-down-to-the-west

Figure 14. Structural features from Stop 9 at the Revlon Outcrop. (A) Outcrop photograph of silicifi ed cataclasite containing non-foliated clasts of metagranite ( CZgr). Scale bar is ~10 cm. (B) Outcrop photograph showing foliated phyllonite clasts ( CZphc) contained within silicifi ed cataclasite. Pencil is 14 cm for scale. (C) Photomicrograph of winged sigma- type porphyroclast of plagioclase in foliated metagranite ( CZgrf). Sense of displacement is down-dip to the west. View is to the south, but rotated 90° to the left. Magnifi cation 2.5×. Field of view 9 mm. (D) Photomicrograph of composite S-C fabric element development in CZphc. Sense of displacement is down-dip to the west. View is to the south, but rotated 90° to the left. Cross-polarized light. Magnifi cation 5×. Field of view is 4 mm. 246 Blake et al.

parallelism with the S1C (Fig. 14D). A penetrative mineral align- the similarities between the two lithodemes. In the vicinity of the

ment lineation, L1, formed from the long axis of quartz ribbons and ﬁ eld trip stop, the west-side-down offset of the FCFZ appears

aggregates or ﬁ lms of platy white mica and chlorite lies in the S1C sufﬁ cient to establish separate lithodemes based on variations in

surface. L1 typically has a dip-slip to oblique, down-dip orientation. composition, texture, and outcrop pattern. Locally, brittle deformation dominates silica-rich domains where Detailed and reconnaissance-level mapping by Parnell quartz defi nes a stair-stepped vein-fi ber lineation and more minor (2012) has determined that basin-bounding structures of the slickenlines aligned parallel to the ductile L1 lineation. FCFZ extend a minimum distance of 10 km past the northern- Based upon similar fi eld relationships, compositions, and most occurrence of Late Triassic clastic sedimentary rocks (Fig. positions along the eastern and western side of the FCFZ, granit- 15) and are most likely represented by the foliated felsic meta- oid rocks observed on opposite sides of this extensional structure intrusive suite ( CZgrf). Because these structures continue north- may represent different structural levels within the same plutonic ward and extend out of the study area, a tip point for the FCFZ body. Distinguishing between them across the FCFZ becomes structure was not determined in his study. Furthermore, Parnell more diffi cult in the northern mapped limits of this structure. (2012) indicates that the termination of these sedimentary rocks The apparent west-side-down offset of the FCFZ progressively does not necessarily mark the northern termination of the struc- becomes less signifi cant northward from Oxford and may explain tural and sedimentary basin at its time of formation. The current

Figure 15. Shaded relief map developed from LiDAR digital elevation data for the Oxford 1:24K Quadrangle showing topographic lineaments that occur along the Coon Creek to Fishing Creek drainage basin. These linear features follow ductile-brittle, normal-slip fault strands of the FCFZ that overprint Carolina terrane rocks. Bold black lines mark the brittle portion of the FCFZ. Other ductile-brittle, normal-slip shear zones in the quadrangle that overprint Carolina terrane rocks are shown in darker gray- scale. Currently mapped Triassic clastic sedimentary rocks ornamented with a stippled clastic pattern. All other rocks in lighter gray. Area north of the horizontal black line crossing the quadrangle mapped by Parnell (2012). Area to south included in Parnell et al. (2006b). Modiﬁ ed from Parnell (2012). Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 247 basin shape, mapped based upon present occurrences of Triassic This stop is mapped as part of the Trcc lithofacies that is in clastic sedimentary rocks, may potentially be a lower structural contact with the Trcs/c lithofacies of Lithofacies Association III level of the basin, compared to the basin at the time of formation described by Hoffman and Gallagher (1989), Clark (1998), and and sedimentary deposition. Clark et al. (2001, 2011). Trcc lithofacies is primarily an irregu- The continuation of these structures suggests that the Tri- larly bedded, poorly sorted, clast-supported to matrix-supported, assic Deep River basin may have been larger during the time boulder to cobble conglomerate. It typically has a micaceous of formation, and perhaps clastic sedimentary rock extended matrix of orange-red gravelly sandstone and reddish-brown silt- farther northward and westward. The continuation of the FCFZ stone. Trcs consists of reddish-brown to dark brown, irregularly structures implies that the extent of the presently mapped basin may be a smaller erosional remnant of a larger basin. However, due to the present inability to establish a tip point for these structures, only a minimum basin size can be determined based upon the nature of the structures that deﬁ ne the FCFZ and the minimum distance they extend northward from Triassic clastic sedimentary rocks. Directions to Stop 10. Turn around and proceed back to I-85 South on U.S. 158. Merge onto I-85 south and travel 2 miles south to the interchange with NC 96 at Exit 204. At the top of the off-ramp turn right (south) and proceed 1.2 miles on NC 96 to the Y-intersection with Fairport Road (CR 1609). Turn left (south), drive 0.6 miles and park on the right side of the road. Outcrops are exposed in the north-facing slopes of the roadside creek. Stop 10 [latitude 36.27269°, longitude −78.57129°].

Stop 10. Polymictic Conglomerate Marking the Northernmost Exposures of Triassic Sedimentary Rocks of the Durham Sub-Basin along the Fishing Creek Fault Zone Location: Western tributary to Coon Creek and its north-facing ﬂ oodplain bluffs along Fairport Road. Map: Oxford 1:24K Quadrangle.

Along the right or south side of the highway and across the roadside ditch serving this tributary to Coon Creek, a stretch of nearly continuous outcrop of Triassic polymictic conglomerate and feldspathic sandstone mark the most accessible and approximately northern limit of sedimentary rocks of the rift basin exposed along the FCFZ (Fig. 4). The last outcrops of coarse conglomerate and interlayered coarse conglomerate and sandstone within the basin have been mapped by Rick Wooten of the Figure 16. Outcrop features from Stop 10. (A) Late Triassic NCGS (initially located on one of Bob Butler’s unpublished fi eld polymictic conglomerate of Lithofacies Association III marking the most accessible and approximately northern limit of sheets) just to the north of this outcrop across the open fi eld, as sedimentary rocks of the rift basin exposed along the Fishing well as a small patch just south of I-85 in the Coon Creek drain- Creek fault zone. Clasts are variable from slightly sub-rounded age basin (Parnell et al., 2006b). No Triassic sedimentary rock to well-rounded pebbles and cobbles that are ~1–20 cm in di- was encountered in mapping north of I-85 (Parnell, 2012). ameter and range from polymineralic granitoids to monominer- The easternmost exposure provides the best example of alic vein quartz. Small beds and lenses of characteristically red- brown, fi ner feldspathic arenite and mudstone are preserved in the coarse clastic nature of this rock unit (Figs. 16A, 16B). The the matrix as well, and have an attitude of approximately N20°E coarse conglomerate is mostly reddish-brown, typical of Triassic and a 10–20° dip to the southeast. The arkosic mineralogy of the sedimentary outcrops, containing a mixture of clast types in mas- feldspathic arenite here and in outcrops between here and Stop sive and chaotically bedded horizons having coarse sandstone to 11 is similar to the metaplutonic rocks of the Carolina terrane gravely sandstone matrix. Some small beds and lenses of fi ner of the central Piedmont. (B) More massively bedded polymictic conglomerate at the east end of the outcrop. A number of the sandstone and mudstone are preserved in the matrix as well, and larger clasts are reminiscent of the weathered intrusive granitoids have an attitude of approximately N20°E and a 10–20° dip to surrounding the Oxford area just to the north at the last fi eld trip the southeast (020,10–20), typical of the strata that dip toward stop. Bedding and clast relationships suggest an ~10 m thick, the east side of the Durham sub-basin (Clark et al., 2001, 2011). coarsening-upward succession for the outcrop from west to east. 248 Blake et al. bedded to massive, poorly to moderately sorted, medium- to and turn left (south) on the highway. Either walk or drive to the coarse-grained, muddy lithic arkosic to pebbly sandstone. fi rst broad dirt driveway on the left (east) side of the road just To the south along the Jonesboro fault, units of Trcc are south of the long stretch of timber that is oriented parallel to the interpreted to be alluvial fan and/or bajada complexes. They are NC 96. Park in the driveway and walk ~0.1 miles eastward to thought to have been generated by progressive dip-slip displace- the outcrops on the left (north) side of the gravel driveway. Stop ment combined with erosion and canyon dissection through the 11A [latitude 36.23795°, longitude −78.57964°] and Stop 11B signifi cant topographic gradient and fault scarp marking the east [latitude 36.23328°, longitude −78.58364°]. side of the Durham sub-basin in the Carolina and Falls Lake terranes. The alluvial fans adjacent to the Jonesboro fault are Stop 11. (A) Quartz Diorite-Tonalite Protomylonite and inferred to have prograded westward from the mouths of crys- Chlorite-White Mica Phyllonite in the West-Dipping talline rock canyons into deepening alluvial depocenters in the Fishing Creek Fault Zone; (B) Disharmonic Folding of Durham sub-basin rift valley (Blake et al., 2001; Clark et al., Chlorite–White Mica Phyllonite of the Fishing Creek 2001, 2011). Fault Zone and the Eastern Contact of the Triassic At this stop, a number of the larger clasts are reminiscent of Durham Sub-Basin the weathered intrusive granitoids surrounding the Oxford area Location: Western tributary to Fishing Creek and northwest- just to the north at the last fi eld trip stop. The arkosic mineral- facing fl oodplain bluffs adjacent to NC 96. ogy of the feldspathic arenite here and in outcrops between here Map: Wilton 1:24K Quadrangle. and Stop 11 is similar to the metaplutonic rocks of the Carolina terrane of the central Piedmont exposed just to the west of the Along the length of the FCFZ as initially described for Stop Durham sub-basin in the Stem 1:24K Quadrangle. Consequently, 9, the development of both ductile and brittle structures marks these outcrops of Lithofacies Association III appear to have been the northeastern border of the Durham sub-basin. At this stop derived from the west or northwest side of the sub-basin. Bed- and in outcrops exposed fairly continuously downstream south- ding and clast relationships suggest an ~10-m-thick, coarsening- ward to the Tar River, the composite fabric element relation- upward succession for the outcrop from west to east. ships and mineralization associated with anastomosing strands The relatively smaller clast size and potential nearby source of this basin-bounding fault zone are well preserved. Reaching area may indicate that conglomerate, sandstone, and siltstone up to a km in width east of basin sedimentary rock exposures, units collectively were deposited in a mixed alluvial fan, debris most of the FCFZ is comprised of phyllite, schist, and gneiss that fl ow and sandy, braided stream environment. They appear to have are actually shear zone phyllonite, protomylonite, and mylonite. derived from and were deposited directly onto metaplutonic, The fault zone rock type depends upon the metagranitoid pro- metavolcanic, and metasedimentary rocks that bound the western tolith type, which ranges from gabbro-diorite to tonalite-trond- border of the sub-basin (Hoffman and Gallagher, 1989; Clark et hjemite and granodiorite-granite. The modal amount and degree al., 2001, 2011; Blake et al., 2003a, 2009). There, the proximal of recrystallization of chlorite versus white mica also infl uences Carolina terrane source rocks of the central Piedmont and the the rock type produced along this structure. Downstream, large half-graben geometry of the Durham sub-basin is more read- hydrothermal, fi ne-crystalline domains of epidotization and ily apparent. The sedimentary-crystalline contact is a regional quartz silicifi cation stand out as large unfoliated bluff outcrops nonconformity that extends from the Oxford region southward within the FCFZ. through at least the Durham–Chapel Hill region. Only locally do Specifi cally at this stop and Stop 11B, gray-green chlorite– fracture zones in crystalline rocks and minor post-depositional(?) white mica phyllonite and protomylonitic gneiss are well exposed faults form the basin boundary along the western border of the as steeply west-dipping outcrops of tens of cm-to-m-scale folia- sub-basin (Clark et al., 2001, 2011; Blake et al., 2009). The litho- tion fi ns (Fig. 17). The surrounding rocks have been mapped as logic character of the sedimentary rocks forming this nonconfor- the foliated equivalents of the tonalite of Gibbs Creek, informally mity in the northwestern portion of the Durham sub-basin is the known as the Gibbs Creek pluton. In fact, much of the southern topic of Stop 14. portion of the wedge-shaped block between the FCFZ and Nut- Directions to Stop 11. Return to NC 96 and turn left (south). bush Creek fault zone to the east (Figs. 2 and 4), as described at Travel 3.4 miles south on NC 96 past the crossroads of Clay and Stop 9, is underlain by this pluton, its foliated equivalent, and its look for a small utility service road on the right (west) side of the northern and eastern border zone, the Tabbs Creek complex (Far- highway. Turn into the circular drive around the substation and rar, 1985b; Grimes, 2000; Blake et al., 2003a; Robitaille, 2004). park. Walk south along NC 96 0.1 miles to the second grassy In hand sample, the Gibbs Creek pluton is a gray-green, lane into the woods to the left (east) side of the highway. Proceed fi ne- to medium-crystalline, unfoliated hornblende biotite tonal- along it to the crest of the hill ~0.25 miles into a clearing, then ite and locally granodiorite. Chlorite, white mica, and epidote turn immediately left (north) and enter into the woods from the recrystallization of the primary igneous minerals marks the clearing. A faint trail will lead down the right side of the ravine greenschist facies metamorphic overprint. Within the pluton, to the rocky, knife edge outcrops lining the southern cutbank of enclaves of microdiorite, foliated amphibolite, meta-ultramafi c Fishing Creek. If the creek is in fl ood stage, walk back to NC 96 rocks, and foliated metagranitoid crop out in random locations Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 249

(Blake et al., 2003a; Robitaille, 2004). The occurrence of micro- shear zone (Figs. 17A–17D). The dominant and more evolved diorite enclaves is a common theme among metamorphosed fabric element is the penetrative metamorphic mineral foliation,

plutons exposed in this portion of the northeastern Carolina ter- S1C. It overprints S1S and deﬂ ects it into a tops-down-to-the-west ′ rane and they may be derived from co-magmatic plutonic bodies. parallelism with S1C, similar to C extensional shear bands. When Diorite-gabbro bodies are exposed just to the northwest in the the spacing between these two foliations reaches cm-scale, large Lake Michie, Stem, and Oxford 1:24K Quadrangles. The foliated down-dip “ﬁ sh-like” phacoids of protomylonite are developed.

metagranitoid enclaves appear to be an early deformed equiva- A penetrative mineral aggregate lineation, L1, is preserved lent of the tonalite that chieﬂ y comprises the Gibbs Creek pluton. from the long axis of quartz ribbons and aggregates or ﬁ lms of

In contrast, the origins of smaller foliated amphibolite enclaves platy chlorite and lesser white mica. L1 develops on the compos-

and four large pods of serpentinite, soapstone and talc-actinolite ite S1S–S1C surfaces. It typically has a dip-slip to oblique, down- schist, and actinolite rock are more problematic. A geochemical dip-to-the-south orientation. Locally, brittle deformation domi- analysis obtained from an amphibolite enclave from the Gibbs nates silica-rich domains where quartz defi nes a stair-stepped Creek pluton has an ocean-fl oor MORB signature and is dis- vein-fi ber lineation and more minor slickenlines aligned parallel

cussed further by Robitaille (2004). The enclaves may represent to the ductile metamorphic L1 lineation. On the chlorite foliation some form of oceanic substrate sampled by this calc-alkaline surface, some vein ﬁ bers display an up-dip sense of slip, indicat- pluton during the magmatic construction of the Carolina Zone ing a reverse component of fault displacement, while shallow- island-arc crustal section. dipping, brittle fault surfaces display a normal sense of vein-ﬁ ber Deformed examples of the Gibbs Creek pluton and associ- growth. Differential, late ductile to brittle dip-slip adjustments ated metagranitoids at this stop and Stop 11B become phyllonite accommodated some FCFZ displacements.

and porphyroclastic protomylonite and mylonite that develop a At Stop 11B, the ﬁ sh-like phacoids, dominant S1S–S1C shear

moderately to steeply west dipping, composite planar-linear fab- foliations, and L1 lineation are also well preserved, but deviate ric striking approximately N10–25°E (010–025). Chlorite, white from the regional trend. In the ditch cut and adjacent small knob,

mica, and biotite again deﬁ ne an S1S schistosity oriented oblique easily observed with Google Earth©, the phyllonite foliation to an S1C, especially adjacent to porphyroclasts of large blue- swings in an arcuate shape from a northeast strike to west-north-

quartz and plagioclase porphyroclasts. At the mesoscale S1S pri- west strike with moderate dips to the southwest. In the ditch, a marily has the shallower dip of the two foliations in this dip-slip few 5–10 cm wavelength multilayer folds of the foliations can

Figure 17. Outcrop and petrographic relationships at Stop 11. Shear sense is tops-down to the right in Figures A–D. (A, B) Gray-green chlorite- white mica phyllonite and protomylonitic gneiss characteristic of the Fishing Creek fault zone exposed at Stop 11A as steeply to moderately dipping, tens of cm-to-m-scale chlorite, white mica, and biotite foliation ﬁ ns. Relict plagioclase and blue quartz porphyroclasts of the tonalite of

Gibbs Creek are preserved between the folia. Composite planar-linear fabric oriented approximately N10–25°E deﬁ ne an S1S schistosity oriented oblique to an S1C. S1S has the shallower dip in this tops-down-west, normal-slip shear zone. Steeper foliation is S1C. (C, D) Oriented photomicrographs of phyllonite showing the shallower S1S and steeper S1C foliations and down-dip extensional recrystallization microstructures on oppos- ing sides of porphyroclasts. Darker areas are chlorite pressure shadows on feldspar and opaque minerals. Views to the south. Magniﬁ cation of

photomicrographs is 1.25× and width of views are 1.7 cm. (E, F) Fish-like phacoids of S1S-S1C shear foliations preserved at Stop 11B. Multilayer folds have 5–10 cm wavelengths, open to tight chevron interlimb angles, northwest-striking and upright to steep-dipping axial surfaces, and gently, northwest-southeast–plunging hinges. The abundant phacoidal ﬁ ns, fracturing, and plentiful quartz veining attest to the brittle overprint on the ductile phyllonite. 250 Blake et al.

be observed (Fig. 17E). Changes in interlimb fold style may be ridges. They are best exposed just northeast of where this fault observed down the length of individual fold hinges. Because of is in contact with the southern tip point of the FCFZ (Fig. 4).

the deviations in foliation orientations, L1 also fl uctuates from the The Jonesboro fault comprises perhaps the most obvious map- northwest to southwest trends and variable plunges. The outcrop scale brittle structure in pre-Mesozoic rocks in the eastern to cen- is also highly and variably fractured (Fig. 17F). Quartz-chlorite tral Piedmont transition. These ridges, highlighted at Mayfi eld tension gashes and vein fi ll permeate the exposure as well. Mountain, were originally described by Carpenter (1970) and The deviation in shear foliation orientation from the regional then Heller et al. (1998), Grimes (2000), Blake et al. (2003a), trend and the highly fractured character of the phyllonite here is and Robitaille (2004). Each mapped a siliceous zone along this interpreted to be caused by rigid-block rotation and transitional- regional ridge line for a distance of ~8 km. Carpenter (1970) also tensile fracturing during late-stage brittle failure immediately mapped a short siliceous zone along the FCFZ just north of its adjacent to the fault contact. Just to the west of this exposure juncture with the Jonesboro fault. Because the Jonesboro fault is and north of the culvert to the north-fl owing stream, the actual the basin-bounding structure on the east side of the Durham sub- contact between weathered phyllonite and sandstone and pebbly basin, it has generally been assumed to be the fault bounding the sandstone is knife-edged and may be depositional or structural. entire length of Triassic sedimentary rock outcrops. This portion of crystalline rocks forms a small, disoriented rider However, mapping in the crystalline rocks east and north of block in the FCFZ on the eastern border of the Durham sub- the Durham sub-basin indicates that the Jonesboro fault contin- basin. Similar geometries have been observed to the south along ues on a N50°E trend out of the basin, crosscutting older crystal- the Jonesboro fault in the Raleigh-Cary region (Bartholomew et line rocks of the Crabtree terrane (Heller et al., 1998; Grimes, al., 1994; Blake and Clark, 2000; Clark et al., 2001, 2011). 2000; Blake and Stoddard, 2004). This structural relationship Numerous anastomosing shear zones crop out in the wedge- then makes the FCFZ become the basin-bounding fault for Tri- shaped region east of the FCFZ. Similar to this stop, those shear assic clastic sedimentary rocks along the northeastern portion zones record tops-down-to-the-west sense of displacement of of the Durham sub-basin. Grimes (2000) and Robitaille (2004) composite planar elements, and dip-slip to slightly oblique-to- demonstrated that the brittle fault here extends for at least two the-south mineral lineation and vein fi bers. A small population of km to another northeast-trending ridge (Fig. 4), locally referred subhorizontal lineations exists when structural data from Parnell to as “Little Egypt Mountain.” Just beyond that point, the fault et al. (2006b), Robitaille (2004), and Parnell (2012) are analyzed. Figure 18 shows an interpreted 3-D view of these shear zones lying east of the Durham sub-basin and FCFZ along the northern portion of this rift basin. Directions to Stop 12. Return to NC 96 and continue south. Travel 5.9 miles to the T-intersection with Philo White Road (CR 1623) on the left (east) side of NC 96. Turn left (east) and drive 1.8 miles to the Y-intersection with CR 1630. Merge right onto CR 1630 and proceed 0.3 miles to the intersection with Flat Rock Road (CR 1629). Turn right (south) and travel 1.9 miles to the base of Mayfi eld Mountain and the driveway to the Stroth- ers’ property on the left (north) side of Flat Rock Road marked by the sign. Drive up the gravel road leading to the top of May- fi eld Mountain and park on the right-hand side of the driveway between the large, black eagle sculptures. Walk 0.1 miles north to the outcrops at the ridge crest. Stop 12 [latitude 36.14427°, longitude −78.53809°].

Stop 12. Silicifi ed and Fractured Cataclasite along the Jonesboro Normal Fault Zone and a Panorama of the Rift-Related Horst-and-Half-Graben System of the Figure 18. Three-dimensional block diagram showing interpreted North-Central North Carolina Piedmont structural characteristics of the northern Durham sub-basin and the Location: Heights of Mayfi eld Mountain and its west-facing Fishing Creek fault zone (FCFZ) within the Oxford 1:24K Quadran- rocky bluffs on the Strothers’ property. gle. Lightest gray shading represents the extent of undeformed Caro- Map: Wilton 1:24K Quadrangle. lina terrane meta-igneous rocks; medium gray shading highlights tops- down-west, ductile-brittle protomylonite and phyllonite zones east of the FCFZ; stippled shading represents the current exposures of Trias- In southeastern Granville County, the brittle normal- sic clastic sedimentary rocks of the Durham sub-basin. They do not slip character of the Jonesboro fault is well exposed along a correspond with the mapped trace of the normal-slip FCFZ highlighted northeast-oriented string of silicifi ed and fractured cataclasite in darkest gray. Modifi ed from Parnell (2012). Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 251 approaches the N10–15°E orientation of the Nutbush Creek fault crystals. In thin section, fractures cut large quartz crystals, while zone (Heller et al., 1998). That Alleghanian dextral-slip fault brecciated quartz occurs with recrystallized quartz as the matrix zone and its ductile-brittle and petrologic relationships were the between larger unfractured and fractured silicifi ed quartz clasts. focus of our Day 1 trip stops. While no vestiges of the host rock to the silicifi cation event can At its top and fl anks, multiply fractured and silicifi ed cata- be identifi ed along the top of the mountain, at lower elevations to clasite underlie Mayfi eld Mountain (Figs. 19A–19C). The rocky the west, brecciated, cataclastic and silicifi ed clasts of Carolina ledges here are massive milky quartz. Subvertically oriented terrane greenstone have been identifi ed (Robitaille, 2004). fractures appear to fall into two main clusters, averaging about Mesozoic and younger(?) brittle faults are more widespread N23°E and N15°W, and highlight the tabular nature of the out- in the Piedmont than the impression conveyed on published crops. A minor group of fractures strike nearly east-west. The geologic maps. Garihan and his co-workers have documented fracture orientation is roughly parallel to the FCFZ, and also an impressive family of faults in the western Piedmont of South similar to trends of diabase dikes in the region. Carolina and North Carolina since the early 1990s (e.g., Gari- Commonly, fracture-fi lled vugs and cavities in outcrop and han et al., 1993). Heller (1996) and Heller et al. (1998) doc- especially fl oat are lined with radiating syntaxial quartz crystals. ument a network of brittle faults in the Lake Wheeler 1:24K These vuggy and locally drusy cavities may also contain the out- Quadrangle south of Raleigh within the Nutbush Creek–Lake lines of silicifi ed breccia clasts in the vug walls (Fig. 19D). Much Gordon fault system. The most extensive of these faults trends of the soil here is littered with small milky quartz pieces and small about N70°W and has been mapped eastward through the Lake

Figure 19. Outcrop and petrographic relationships at Mayfi eld Mountain and Stop 12. (A, B) Brittle normal-slip character of the Jonesboro fault is visible along northeast-oriented silicifi ed and fractured cataclasite rocky ledges. Subvertically oriented transitional-tensile fractures highlight the tabular nature of the outcrop and ridgeline. Tyler Stewart, University of North Carolina Wilmington geology undergraduate student, kneeling for scale in (A). Kenny Robitaille and Brian O Shaughnessy, UNCW geology students, standing for scale on the ridgeline of Mayfi eld Mountain just north of Stop 12 in (B). (C, D) Multiply fractured and silicifi ed cataclasite domains on the western slopes of Mayfi eld Mountain, and mineral-fi lled vugs and cavities in outcrop and especially fl oat at the top of the ridgeline lined with radiating syntaxial quartz crystals. Vuggy and locally drusy cavities may also contain the outlines of silicifi ed breccia clasts in the vug walls. Hammer head is 12 cm wide in (C). View to the east. Hand samples in (D) are ~5 cm in width; tips of fi ngers in lower left. 252 Blake et al.

Wheeler and into the Garner 1:24K Quadrangle for ~12 km cataclastic blocks of foliated felsic Little Creek gneiss of the (Heller et al., 1998). Crabtree terrane mark the apparent northern tip point for the Reconnaissance mapping by McDaniel (1980) in the north- Jonesboro fault. ern portion of the eastern Piedmont showed numerous occur- The Wilton pluton is a Pennsylvanian-Permian granite rences of “quartz breccia” and other presumably brittle features, that intrudes both the Falls Lake and Crabtree terranes (Car- suggesting the presence of other regional brittle faults. Since that penter, 1970; Stoddard et al., 1991; Blake et al., 2003a, 2003b; work, numerous silicifi ed cataclasite and silica-rich ridges and Robitaille, 2004). It is exposed in the fault block to the east. It extensional strike-parallel and strike-normal faults have been forms part of the amphibolite facies horst block to the green- mapped along the length of the Nutbush Creek–Lake Gordon schist facies half-graben block to the west underlain by the fault system (Phillips et al., 2002; Stoddard et al., 2002; Buford et Gibbs Creek pluton. A small quarry across the road from the al., 2007; Blake et al. 2010), including Stop 3 yesterday. In many Strothers’ driveway exposes an undeformed portion of this plu- places, these brittle faults and possibly extensional crack-fi ll are ton. Carpenter (1970) observed brecciated granite in at least also expressed topographically by these relatively sharp, but dis- one locality along its western margin. Along its eastern margin continuous ridges. Silicifi ed breccia and microbreccia are com- ~2 km to the east, the granite records a subhorizontal stretch mon along such faults, but usually the only evidence is rugged lineation. This L-tectonite marks the western boundary and outcrops of milky quartz, syntaxial quartz veins, or linear arrays strain gradient into the renamed Neuse River fault zone. This of vein quartz, silicifi ed cataclasite and locally vuggy quartz structure extends southward as the Falls Lake fault between the fl oat. Cataclasite in the Lake Wheeler region contains clasts of Falls Lake terrane to the west and the Crabtree terrane to the country rock also interpreted to be derived from a level above the east (Stoddard et al., 1986, 1991, 1994). present erosion surface (Heller, 1996). Slickenlines and fi bers are In older models of the Piedmont, the Jonesboro fault would observed locally (Heller et al., 1998). mark the boundary between the Raleigh metamorphic belt and Looking north and west from Stop 12, the topographic the Carolina slate belt along the western fl ank of the Wake- expression and horst-half graben geometry of the northern ter- Warren anticlinorium. Recent mapping supports the concept that minus of the Durham sub-basin is evident. To the very far west, this fault is a fundamental lithologic break and metamorphic dis- prominent ridges of the Carolina terrane in the central Piedmont continuity between an infrastructural block to its east and a series are visible along the skyline in the Stem and Lake Michie 1:24K of suprastructural blocks to its west (Robitaille, 2004; Parnell, Quadrangles, the location of our next two stops. The most promi- 2012; Blake and Stoddard, 2004). Older maps and fi eld guides nent conical peak is Bowling Mountain near Tallyho. Weathering have proposed that the supracrustal block was perhaps a green- resistant pyrophyllite- and silica-enriched hydrothermal depos- schist facies equivalent of the infrastructural Falls Lake terrane its within metamorphosed dacitic metavolcanic rocks of the to its south. This hypothesis was based on the similarity in con- Hyco Formation underlie that peak (Sexauer, 1983; Rhodes and tact relationships among metamorphosed mafi c and ultramafi c Blake, current unpublished STATEMAP mapping). These 630– enclaves and pods in matrix. Thus, Stoddard et al. (1997) origi- 615 Ma Virgilina sequence pyroclastic and volcanogenic sedi- nally proposed that the Jonesboro fault juxtaposed two different mentary rocks underlie most of the region in the western distance. crustal and structural levels of the same terrane, perhaps the Falls Lithodemes of post–613 Ma metamorphosed calc-alkaline intru- Lake terrane. sions as viewed at Stop 9 underlie the region in the northwestern Leaving Mayfi eld Mountain, the fi eld trip heads westward distance. These metamorphosed plutons form a belt of magma- on NC 56 over Falls Lake terrane schist, gneiss and meta- tism that extends northeastward past the Oxford region and then ultramafi c rocks, a bluff slope of silicifi ed cataclasite mark- to Kerr Lake as the 571 Ma Vance County tonalite-granodiorite ing the Jonesboro fault, and then the Gibbs Creek pluton and pluton emphasized yesterday at Stop 7. associated mafi c and meta-ultramafi c enclaves (Fig. 4). Another The depression between those far peaks and the north- slope break marks the FCFZ, and sequentially westward across south ridge in the near distance is occupied by Triassic rift- the Durham sub-basin, units of Lithofacies Association III and related clastic sedimentary rocks and is the Durham sub-basin. then II are crossed all the way to the Butner-Stem region. There, We will travel across this basin to the next two stops. The horst the Jurassic Butner diabase sill underlies much of the town of block to the sub-basin half-graben lies along this near distance Butner (NCGS, 1985; Gottfried et al., 1991) and rounded boul- north-south ridge just west of Mayfi eld Mountain. The green- der debris lines many of the local roads. The Sunrock Group’s schist facies Gibbs Creek pluton and its plethora of metamor- Butner quarry of diabase “trap rock” is located on the outskirts phosed mafi c and ultramafi c enclaves underlie it. This region is of southeastern Butner. Some samples removed from that the wedge-shaped block located between the FCFZ on the far quarry indicate coarse crystal accumulation in the interior of the west side of this ridge and the Jonesboro fault–Nutbush Creek Butner sill including 5–10-cm-long prismatic clinopyroxene fault zone between this stop and Stop 7 yesterday (Figs. 2, 3, 4, crystals. In most outcrops, the melanocratic diabase is medium and 18). The Jonesboro fault continues to the north of Mayfi eld crystalline containing up to 3–4 mm tabular subidiomorphic Mountain as a cataclastic structure for at least 25 km to Red plagioclase prisms, xenomorphic intergranular clinopyroxene Bud Creek in the central Henderson 1:24K Quadrangle. There, and opaque minerals including pyrite, and very minor olivine. Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 253

Locally, some diabase is fi nely aphyric, especially on the rims Stem pluton (Fig. 20A). Moving east away from the lake, of sills or some small dikes. south-side slope outcrops and cobble fl oat becomes progres- Directions to Stop 13. Return on the gravel driveway to Flat sively foliated and fractured into a non-penetrative ductile- Rock Road and turn left (east). Travel 1.0 mile to the T-inter- brittle fault zone. The creek cuts obliquely across this fault section with Grove Hill Road (CR 1625). Turn right (south) zone for ~0.25 km. Upstream, undeformed tonalite becomes and drive 0.4 miles to the intersection with NC 56. Turn right the dominant rock and appears to mark the eastern boundary (west) and drive 9.3 miles straight through the crossroads of of this structure. Wilton, downtown Creedmoor and NC 50 to the T-intersection In between its two boundaries, discrete steeply to sub- with U.S. 15. Turn left (south) at the traffi c light onto NC 56/ vertically east- and west-dipping planar shear zones of com- U.S. 15 and then immediately right (west) at the next traf- posite white mica-chlorite foliation, subparallel fractures, and fi c light, staying on NC 56. Continue 2.6 miles westward on crosscutting fractures overprint tonalite of the Stem pluton NC 56 to the town of Butner, North Carolina, and the I-85 cor- (Fig. 20B). In some exposures, discrete planes of recrystal- ridor. Proceed 0.6 miles across I-85 and past the Asian King lized white mica and chlorite along with tensional fractures restaurant on the right to the traffi c light at S. 33rd Street. Turn subdivide the tonalite into large fi n-like phacoidal shapes as right (north) and proceed 2.1 miles to the intersection with But- they anastomose through the rock (Fig. 20C). Strikes of these ner Road/Old 75 Hwy (CR 1004). Turn right (north) and drive surfaces vary from N15°W to N15°E. In other outcrops, the 1.2 miles to the left (west) turn with Barham Eason Road and phyllosilicate planes become fi nely spaced, and anastomose to Camp Eason Murdoch. If the yellow gate to Camp Eason Mur- form lenticular to wedge-shaped domains of recrystallized and doch is closed, walk 0.5 miles west down the road, and just relic quartz-feldspar, basically a gneissic protomylonitic struc- before the facility and its gate, turn immediately right (north) ture analogous to the FCFZ rocks observed at Stops 9 and 11. and walk into the woods and toward the steep bank of the creek. These wedge shapes are elongated in both the strike-slip and Stop 13 [between latitude 36.17906 °, longitude −78.76353° dip-slip direction, further highlighting the composite nature of and latitude 36.17951°, longitude −78.76082°]. the steep foliations. As microdiorite enclaves are encountered locally, they Stop 13. Ductile-Brittle Fabric Elements and Faulting in become dark green white mica-chlorite phyllonite. When the the Neoproterozoic(?) Stem Tonalite-Granodiorite Pluton strain in the pluton and enclaves is penetrative, these zones will along the Western Boundary of the Triassic Durham erode as subvertically oriented fi ns protruding up from the creek Sub-Basin at Lake Butner bottom. The prominent foliation surfaces also contain a felsic rod Location: Eastern tributary to Lake Butner off Barham Eason and white mica-chlorite aggregate mineral lineation. Oriented Road below Camp Eason Barham, formally Murdoch. with dip-slip and oblique-slip plunges, the mineral alignment Map: Lake Michie 1:24K Quadrangle. appears to be a stretch lineation in these anastomosing shear zones. Transitional-tensile fracture surfaces may also record this Underlying much of the stop here and to the east in the Stem lineation as vein fi bers of white mica-chlorite, felsic rods, and 1:24K Quadrangle, metamorphosed tonalite and granodiorite of Fe-oxide-hydroxide coatings. the Stem pluton is leucocratic (CI < 10), light tan gray-white, blu- Preliminary analysis indicates that the shear-sense popula- ish gray-white, or pinkish-white depending upon weathering and tion is tops-down in both east- and west-dipping surfaces in this amount of primary biotite, hornblende, or metamorphic chlorite, zone and similar zones regionally. Local populations of up-dip and then K-feldspar content. White-tan plagioclase and blue-gray vein-fi ber shear sense similar to that at the FCFZ may be encoun- quartz are dominant phenocrysts. Porphyritic outcrops containing tered. In addition, fractures and crosscutting veins may be lined plagioclase, blue quartz, and large pink K-feldspar phenocrysts with quartz prisms or multiple layers of wall-lining quartz miner- defi ne magmatic domains of granodiorite in the tonalite. Dikes alization in a crack-seal, syntaxial growth pattern (Fig. 20D). The of trondhjemite, monzonite and granodiorite locally crosscut the fault zone also appears to serve as a conduit for a Jurassic diabase tonalite. All plutonic types appear to contribute signifi cantly to dike. The dike has been mapped for at least 3 km north and south the arkosic composition of sandstone that nonconformably over- of Stop 13 at an acute angle to this structure. lies them ~1 km just to the east in the Durham sub-basin. This This fault zone extends ~2 km northeast from the Lake relationship is the topic of Stop 14A. In addition, cm-to-m-scale Michie into the Stem 1:24K Quadrangle. There, it continues enclaves of greenstone, either very fi ne-crystalline microdiorite for at least another 4 km before apparently reaching a tip point or andesite, are conspicuous throughout the pluton. This relation- nestled in between a series of northeast-trending, ductile- brittle ship appears in many of the 613–571 Ma Carolina terrane calc- fault zones. Within both the Stem and Lake Michie 1:24K alkaline plutons exposed from here eastward to its eastern terrane Quadrangles, a series of these ductile-brittle fault zones having boundary at the Nutbush Creek fault zone. an en echelon distribution are beginning to be recognized on At the west end of this series of stream bluffs along this the northwestern side of the half-graben marking the Durham unnamed tributary just before it deepens into Lake Butner, sub-basin. They typically have high-angle dips and are N15°W- undeformed hillside outcrops belong to the informally named N15-30°E–trending. They contain both subvertically to steeply 254 Blake et al.

Figure 20. Outcrop relationships at Stop 13. (A) Fault zone protolith of medium- to coarse-crystalline, hypidiomorphic to xenomorphic granular tonalite of the Stem pluton containing conspicuous porphyritic blue quartz phenocrysts up to 2–4 mm in diameter. Pen is 11 cm in length for scale. (B, C) steeply to subvertically east- and west-dipping discrete planar shear zones of composite white mica-chlorite foliation, subparallel fractures, and crosscutting fractures overprinting Stem pluton tonalite. Relic phenocrysts preserved to produce a felsic porphyroclastic plagioclase-quartz gneiss protomylonite. Pen and pencil are 11 and 16 cm in length, respectively, for scale in (B) and (C). View to the northeast in (B). (D) fractures and crosscutting veins lined with quartz prisms or multiple layers of wall-lining quartz mineralization overprinting the protomylonitic foliation in a tonalite gneiss in a crack-seal, syntaxial growth pattern. Float sample is ~7 cm in width.

east- or west-dipping composite shear foliation-fracture surfaces, dacite unit, especially across the top of Bowling Mountain. There as well as overprinting silicifi ed cataclastic structures and vari- pyrophyllite phyllonite is exposed. The fault zone from this stop ably mineralized zones. has been traced at least as far north as these faults just east of In the Stem pluton, and diorite and granodiorite of the Bowling Mountain. The origin of these ductile-brittle fault zones Butner stock to the west just across Lake Butner, along-strike is not yet clear and they have the potential to be younger struc- domains of silicifi cation, epidotization, and sulfi de, primarily tures, perhaps related to Taconic, Alleghanian, or more likely, pyrite, mineralization overprint the northeast-striking phyllonite Permo-Mesozoic extensional deformation. and protomylonitic to mylonitic composite foliation and down- Directions to Stop 14. Return to Butner Road/Old 75 Hwy dip lineation of white mica, quartz ribbons, plagioclase, and and proceed south for 1.6 miles to the T-intersection with Range orthoclase. Locally, highly altered, stained and leached outcrops Road on the right (north). Pass Range Road and drive another of pyrite, Fe-oxide-hydroxide, and silica mark these zones. Fur- 0.3 miles, crossing Knap of Reeds Creek, and park in the small ther to the west, composite facies of trondhjemite, granodiorite, gravel/grass driveway on the right (north) side of the highway and granite of the 613–614 Ma Moriah pluton may be foliated or and on the east side of the NCSU Umstead Agricultural Field non-foliated. Both types display some silicifi cation or signifi cant Research Unit. Walk 0.1 miles back (east) to Knap of Reeds sericite-silica and leaching overprint. Creek and proceed upstream to the rocky bluffs on the left Other outcrops additionally display heavy Fe-oxide- (west) side of the creek and Stop 14A [latitude 36.15684°, lon- hydroxide staining. Recently, another series of these fault zones gitude −78.77468°]. has been discovered. They have a northeast strike in the north- Then, walk 0.1 miles west past the 3 abandoned houses of eastern Lake Michie 1:24K Quadrangle (Rhodes et al., 2012). the Umstead Facility to the north-oriented, grass-covered access They crosscut the northeastern border zone of the Moriah pluton, road on the east side of the Umstead Facility. Proceed up the large bodies of microdiorite, and the country rock Hyco Forma- grass road to the 2 large rock blocks and then turn immediately tion dacite lavas and tuffs unit (Zdlt) exposed east of the pluton. left (west). Proceed downstream to the outcrops on the right cut- They also affect the hydrothermally altered equivalent of this bank and Stop 14B [latitude 36.15531°, longitude −78.78218°]. Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 255

Stop 14. (A) Bluff-Scale Alluvial Fan Crossbeds in Triassic is lithic arkosic sandstone. Individual grains and clasts straddle Pebbly Arkosic Sandstone of Lithofacies II, Durham Sub- the sand-to-gravel-sized transition, having lengths up to 2–4 mm. Basin of the Triassic Deep River Rift Basin; (B) Cutbank Randomly scattered and small-scale domainal accumulations of of Triassic Sedimentary Breccia of Metamorphosed Hyco angular to subrounded monomineralic quartz pebbles are also Formation Microdacite-Diorite in Mudstone Matrix preserved within this coarse-grained matrix. They are reminis- Location: (A) Prominent west-facing rocky bluffs on Knap cent of some of the quartz veins and tension gashes overprint- of Reeds Creek in the northwest quadrant of the intersection ing meta-intrusive rocks just to the west such as the Stem and between Range Road and Butner Road, and (B) Hillside and cut- Moriah plutons and Lake Butner stock (McConnell and Glover, back outcrops on southeast facing cutbacks of an unnamed creek 1982; Blake et al., 2009). The coarse grain size and composition and the Umstead Facility and North Carolina State Game Lands of the matrix would also be indicative of the coarse crystal size access road. and composition of its source region rocks, also likely to be these Map: Lake Michie 1:24K Quadrangle. metamorphosed granitoid rocks. While there is a distinct pink coloration to some of the feld- When hiking to Stop 14A and Knap of Reeds Creek, turn spars, it is not clear whether all such hues are due to the actual right (southeast) and look across Old 75 Highway at the broad color of orthoclase feldspar or a secondary mineral overprint. The lobate topography upon which the large agricultural barns of term “pinking” is commonly used to describe secondary recrys- the Umstead facility are built. This broad hill is the remnant of a tallization and alteration of plagioclase feldspar to K-feldspar or shallowly east-southeast–dipping slope of arkosic sandstone. It perhaps other minerals due to hydrothermal geochemical diffu- is tentatively ascribed to the sandstone with interbedded siltstone sion, fl uid migration, and cation exchange (e.g., Bartholomew unit (Trcs/si2) of Lithofacies Association II (Hoffman and Gal- et al., 2009; Dennis, 2010). “Pinking” of feldspar is common in lagher, 1989; Clark et al., 2001, 2011) that is mapped in much of eastern Piedmont granitoid rocks of North and South Carolina the Durham sub-basin here. This sandstone lobe thickens back to and Virginia. Alleghanian plutons display a strong hydrother- the west where it unconformably overlies metamorphosed Caro- mal overprint of feldspar “pinking,” especially along or adjacent lina terrane metavolcanic and metavolcanogenic sedimentary to the borders of the Mesozoic rift basins. The Pennsylvanian- rocks of the Hyco Formation (Fig. 4). Enter into the woods on the Permian Lilesville granite pluton, which is exposed adjacent to left (west) side of Knap of Reeds Creek and walk the fl at upper the Triassic Wadesboro sub-basin in the southern portion of the slope in the tree line that appears to be an old road. Walk along Deep River rift basin, and the Pennsylvanian-Permian Petersburg this fl at area upstream to a narrow, V-shaped cut in the steep bank granite, which lies along the eastern fl ank of the Richmond rift and descend to the stream. basin, both record strong, late-stage overprinting “pink” events. The small rocky slope at the creek is weathered arkosic In these arkosic sandstone samples, there are clearly small, sandstone similar to the lobe across the road. Turning left (north- pink grains that display Carlsbad twining. However, domains west), an east-dipping layer of Triassic mudstone is exposed in of white-tan plagioclase transition into domains of “pinking” the brush that lines the steep creek bank. It is primarily reddish- and many are coated with Fe-hydroxide mineralization, mak- maroon in color, but is variegated in pale green colors at a high ing visual estimates of mineral percentages a challenging task. angle to the thinly laminated bedding planes. The mottled col- In fact, along the noncomformity, the proximity and mineralogy oring suggests that paleobioturbation is now recorded as Fe- of the source rocks combined with indurating silica-clay min- oxidized regions surrounded by pale green, greenish-blue, or eral cement makes sandstone outcrops resistant to erosion. When gray reduced Fe-domains within the mudstone. Walking just combined with the “pinking” mineralization, sandstone can be upstream from the mudstone, a 6–7-m-high, subvertically ori- confused with equigranular granitoids in small pavement out- ented cutbank and a 3–4-m-wide and fl at, lobate stream outcrop crops that lack larger identifying pebbles right along the noncon- of arkosic sandstone are well exposed. Along much of the length formity contact. Some form of “pinking” is evident in the matrix of this nonconformity in the Lake Michie and Stem 1:24K to the arkosic sandstone at this stop. It contributes to the overall Quadrangles, arkosic sandstone is the consistent pediment rock pink coloration of the steep cutbank bluff. Perhaps the local asso- type deposited upon variable crystalline basement rock types. It ciation of diabase sills and meteoric waters contributed to a weak also appears to be the dominant rock type along the northwest- hydrothermal “pink” overprint of this arkosic sandstone. ern border of the Durham sub-basin. In any case, large-scale stratifi cation of the pink-white arkosic Here, the sandstone is coarse grained, poorly sorted and sandstone is a well preserved sedimentary structure here. Bound- poorly rounded. It is pinkish-gray, light gray or light tan in color. ing surfaces of individual crossbeds reach sizes of 2–3 m. They The matrix assemblage includes blue-gray quartz, white-tan may have their foreset and bottomset beds lined with individual plagioclase, minor K-feldspar, white mica, and biotite. Cleav- and accumulations of pebble-sized clasts in this subvertically ori- age surfaces on both feldspar types and conchoidal fracture of ented, 2-D bluff view. Accumulations of pebbles in the large, fl at blue-gray quartz are clearly preserved in single minerals. Some stream outcrop may be adding to a 3-D record of this sedimentary matrix clasts are actually metagranitoid rock fragments con- structure on shallow east-dipping foreset and bottomset surfaces. taining one or more of these minerals so that in part this unit These crossbeds appear to be large, subaqueous dune structures 256 Blake et al. possibly deposited in a mixed alluvial fan, debris fl ow and sandy, primarily angular to subrounded and are randomly distributed in braided stream environment. Paleocurrent directions derived from a red-brown mudstone matrix. Many of the clasts are metamor- the crossbeds and the N20–40°E (020–040) strike and shallow east phosed diorite or its highly silicifi ed and epidotized equivalent. dip of beds suggests that the sediments were derived from the west Some clasts are rounded vein quartz. side of the Durham sub-basin (Figs. 21A, 21B). Just upstream metamorphosed, locally fractured, and then Just upstream to the north, just below the lowermost set of foliated plutonic rocks of the Butner stock crop out. They are crossbeds in this arkosic sandstone layer, a thick layer of maroon mesocratic to melanocratic (CI = 40–70), greenish-gray to micaceous mudstone to fi ne muddy sandstone is exposed. grayish-green to green, fi ne- to medium-crystalline diorite, The orientation of thicker bedding laminations and fi ssility in microdiorite and quartz diorite. Textures range from equigranular thinly bedded layers, as well as the disconformable sandstone- to porphyritic. Hypidiomorphic to xenomorphic granular plagio- mudstone contact, further attest to the shallow east dips of the clase and hornblende phenocrysts range up to 1–3 mm in tabular sedimentary rocks here. This mudstone can be traced around the length. Plagioclase crystals are highly saussuritized and to a lesser bend of Knapp of Reeds Creek to a small south-fl owing tributary. degree sericitized. Some crystals display evidence of epidote- There, the mudstone appears to disconformably overlie sedimen- enriched Ca-rich cores and sericite-enriched Na-rich rims at both tary breccia. Clasts that range from several mm to 10s of cm are the meso- and microscales. Hornblende may be recrystallized to

Figure 21. Outcrop relationships at Stops 14A and 14B. (A, B) Large-scale stratifi cation of pink-white feldspathic arenite well preserved as the dominant sedimentary structure at Stop 14A. Bounding surfaces of individual crossbeds reach sizes of 2–3 m. Upstream, just below the lowermost set of crossbeds in this feldspathic arenite layer, a thick layer of maroon micaceous mudstone to fi ne muddy sandstone is exposed. Location is interpreted to be part of Lithofacies Association II. Paleocurrent directions derived from the crossbeds and the N20–40°E (020–040) strike and shallowly east-dipping beds suggests that the sediments were derived from the west side of the Durham sub-basin. Todd LaMaskin, University of North Carolina Wilmington geology professor, is 1.8 m tall for scale. Both views to the southwest. (C) Intermixed Triassic sedimentary breccia and conglomerate of Lithofacies Association III at Stop 14B. Clasts range from several cm to over 50 cm in length. Clasts are chiefl y metamorphosed aphanitic and weakly porphyritic hornblende and plagioclase dacite underlying the stream bluff and land immediately to the north of the creek. Hammer is 28 cm in length. View to the southwest. Alleghanian Nutbush Creek fault zone and Deep River Triassic basin 257

chlorite, epidote, and actinolite+opaque minerals. Locally, some tary rock types and environments. Deposition appears to include, outcrops contain 5%–10% quartz, classifying them as a quartz from west-to-east into the sub-basin, pediment and then a tran- diorite. Where foliated, chlorite and white mica highlight the sitional and laterally changing gravel- to sand-sized alluvial overprinting composite phyllonite foliation-fracture. fan, debris or braided stream, and/or intermittent stream system, Now return to the north-northwest–oriented, grass-covered including subaqueous dune deposits. access road on the east side of the Umstead facility. Continue As currently mapped, these outcrops in the Lake Michie and southwest down Old 75 Highway 0.2 miles to the grassy access Stem 1:24K Quadrangles have been grouped with the region-

lane on your right (north). It will be located immediately across ally, and northern sub-basin–dominant Trcs/si2 unit of Lithofa- the road from the lobate sandstone hillside and the large barns cies Association II (Hoffman and Gallagher, 1989; Clark et al., and offi ces of the Umstead Agricultural Facility on the south 2001, 2011; Blake et al., 2009). This unit contains sandstone with side of the road. Turn immediately right (north) and walk up interbedded siltstone. The sedimentary sequence distribution is this grassy lane. It is clearly marked as the unimproved road on attributed to lateral point bar aggradation within a meandering the Lake Michie 1:24K Quadrangle. Travel ~0.25 miles until fl uvial system. Vegetated fl oodplains are interpreted to have sur- you encounter several very large blocks of aphanitic gray-green rounded this depositional environment. Abundant K-feldspar and metadacite on the left (west) side of the lane. Turn immediately white mica and the coarse- to very coarse-grain size indicate a left (west) and cross the small fl oodplain to the unnamed south- proximal granitic source area. fl owing tributary to Knap of Reeds Creek and Stop 14B. In the south-central Lake Michie 1:24K Quadrangle just

Along the western cutbank of this stream, intermixed Trias- southwest of this stop, the Trcs/si2 unit is in contact with the sic sedimentary breccia and conglomerate are well exposed (Fig. Trcs/si1 unit of Lithofacies Association I (Hoffman and Galla- 21C). Clasts range from several cm to 30 cm in length. Some gher, 1989; Clark et al., 2001, 2011; Blake et al., 2009). This clasts are over 50 cm in length. The larger clasts primarily have unit contains sandstone with interbedded siltstone as well. The angular to subangular shapes. Smaller clasts tend to be more sub- sandstone sequences are interpreted to represent sandy braided rounded to rounded or oblate in shape as if tumbled and trans- streams, perhaps in an alluvial fl oodplain environment. Thick ported farther. These clasts are chiefl y the metadacite encoun- sequences of heavily bioturbated siltstone surround these braided tered on the grassy lane. It underlies the stream bluff and land streams. Their interlayering is interpreted to indicate channel immediately to the north of this creek. Many clasts are mesocratic avulsion on a muddy fl oodplain, perhaps as these braided alluvial (CI ≈ 30–40), gray-green, aphanitic and weakly porphyritic horn- fan streams prograded eastward. blende and plagioclase dacite, indicating a proximal source area. Along the northwestern border of the Durham sub-basin, Hornblende and plagioclase phenocrysts are not ubiquitous in similarities in sedimentary facies characteristics, lateral interlay- metadacite and some blocks and local outcrops are micro-quartz ering of sediment supply and alluvial-fl uvial depositional envi- diorite based upon mineralogy and texture observed in thin sec- ronment blurs the ability to make a sharp distinction between tion. Oblate clasts are foliated and represent deformed equiva- these two lithofacies association units. Because these sedimen- lents of metadacite and mixed volcanogenic sedimentary and tary similarities can be traced northeast to their termination pyroclastic rocks. One of the northwest-striking, ductile-brittle against the FCFZ, evident at Stop 11B, much of the very north- fault zones oriented parallel to the sub-basin border is exposed ern portion of the Durham sub-basin is underlain by sedimen- ~0.5–1.0 km north of this location. tary rocks formed in highly similar depositional environments. Stops 14A and 14B provide a localized cross section through In these units, basal layers of coarse sedimentary conglomerate some of the sedimentary sequences and depositional environ- and breccia are also a signifi cant component along the border ments that mark the western border of the Durham sub-basin. nonconformity (Parnell et al., 2006b). The sub-basin geometry, Arkosic sandstone underlain by mudstone and sedimentary con- structure, and sedimentary characteristics highlight the central glomerate and breccia are mapped discontinuously along this Piedmont and northeastern Carolina terrane, and their underlying contact to its northern termination at the FCFZ (Parnell et al., calc-alkaline metagranitoids as a principal source area and rock 2006b; Blake et al., 2009). types for the infl ux of clastic material into this growing rift basin. Similar to the east side of the sub-basin, an alluvial fan Mapping here is compatible with earlier interpretations of basin depositional environment is proposed for this portion of the growth and lithofacies association development in the northern western border of the Durham sub-basin. Depositional sequence portion of the Durham sub-basin and the Triassic Deep River rift geometry and rock types are consistent with an abundant sup- basin in general (Hoffman, 1994; Hoffman and Gallagher, 1989; ply of proximal and distal gravels and sands of metamorphosed Olsen et al., 1991; Clark et al., 2001, 2011). and locally foliated intrusive, extrusive and sedimentary origin. End of Day 2. Return to vehicles on Butner Road/Old 75 Neoproterozoic to Cambrian Carolina terrane rocks to the west Hwy and proceed north for 0.7 miles back to the T-intersection are the inferred source for these sediments. East-dipping sedi- with 33rd Street. Turn right (east) on 33rd Street and then imme- mentary beds and local paleocurrent directions from sedimentary diately right (south) on Central Avenue. Proceed east along crossbeds distributed along the western border of the Durham Central Avenue 1.2 miles to the stop sign at Veazey Road. Turn sub-basin indicate an eastward prograding sequence of sedimen- left (east), continuing to follow Central Avenue straight through 258 Blake et al. downtown Butner. There are several rest facilities and conve- Bartholomew, M.J., Fleischmann, K.H., and Wilson, J.R., 1994, Structural fea- nience stores in Butner. Drive 1.8 miles to the east side of But- tures associated with the Jonesboro fault where it crosses U.S. Highway 70, Wake County, North Carolina, in Stoddard, E.F., and Blake, D.E., eds., ner and the interchange with I-85 South at Exit 189. Merge right Field Trip Guidebook for the 1994 Carolina Geological Society annual down the on-ramp and travel 151 miles to Exit 38 and I-77 South. meeting, p. 69–74. Follow the traffi c fl ow and signs for I-77 South. Merge onto I-77 Bartholomew, M.J., Evans, M.A., Rich, F.J., Brodie, B.M., and Heath, R.D., 2009, Rifting and drifting in South Carolina: Fracture history in Allegha- South and travel 4 miles to Exit 9 and I-277. Follow the signs for nian granites and Coastal Plain strata, Field Trip Guidebook for the 2009 I-277 and U.S. 74 East and proceed 1.2 miles to South College Carolina Geological Society annual meeting, Columbia, South Carolina. Street. Merge right and onto the off ramp. Then travel east on Becker, S.W., and Farrar, S.S., 1977, The Rolesville batholith, in Costain, J.K., Glover, L., III, and Sinha, A.K., eds., Evaluation and Targeting South College Street to the Charlotte Convention Center and the of Geothermal Energy Resources in the Southeastern United States: end of the fi eld trip. U.S. Department of Commerce National Technical Information Service VPI&SU-5103-3, p. A53–A77. Biles, R., 2005, The rise and fall of Soul City: Planning, Politics, and ACKNOWLEDGMENTS race in recent America: Journal of Planning History, v. 4, p. 52–72, doi:10.1177/1538513204269993. We want to thank the landowners for access to their prop- Blake, D.E., 1986, The geology of the Grissom area, Franklin, Granville, and Wake Counties, North Carolina: A structural and metamorphic analysis erty for the fi eld trip stops. These include: Mr. and Mrs. Strother, [M.S. thesis]: Raleigh, North Carolina State University, 300 p. Mr. Troy Preddy, Mr. Ronald Stainback, Mr. and Mrs. William Blake, D.E., 2008, Geologic map of the Raleigh West 7.5-minute quadrangle, Landen, Mr. and Mrs. David Holliday, Mr. Stephen Bailey, Mr. Wake County, North Carolina: North Carolina Geological Survey Geo- logic Map Series 15, scale 1:24,000. and Mrs. Charles Ellis, Ms. Mattie Bell, Mr. Bob Junk, Mr. Leon- Blake, D.E., and Clark, T., 2000, Geologic map of the Cary 7.5-minute Quad- ard Hite, and Ms. Shirley Royster, as well as the staff of Kerr rangle, Wake County, North Carolina: North Carolina DENR Geological Survey Open File Report 2000-2, 1:24,000-scale map, in color. Lake State Recreational Area, especially Charles W. Shelton, Blake, D.E., and Stoddard, E.F., 2004, Manuscript geologic map of the Hender- Park Ranger III. son 7.5-minute Quadrangle, Vance County, North Carolina: North Caro- The northern portion of the area covered by the trip was pre- lina Geological Survey, scale 1:24,000, in color. Blake, D.E., Clark, T.W., and Heller, M.J., 2001, A temporal view of terranes viously mapped by Bob Druhan and the late Bob Butler, as part and structures in the eastern North Carolina Piedmont, in Hoffman, C.W., of their study of crystalline rocks along the Nutbush Creek fault ed., Field Trip Guidebook, Geological Society of America Southeastern zone. The portion of their study lying within the John H. Kerr Section, v. 50, p. 149–180. (This paper is available as item 2012333 in the GSA Data Repository at http://www.geosociety.org/pubs/ft2012.htm, or Dam Quadrangle was incorporated in the USGS South Boston on request from [email protected].) 30′ × 60′ preliminary geologic map (Horton et al., 1993a). We Blake, D.E., Robitaille, K.R., Phillips, C., Witanachchi, C., Wooten, R.M., thank Bob Druhan and Wright Horton for sharing their data with Grimes, W., Pesicek, J.D., and Grosser, B.D., 2003a, Manuscript geologic map of the Wilton 7.5-minute Quadrangle, Vance County, North Carolina: us. The southern portion of the fi eld trip area was mapped by North Carolina Geological Survey, scale 1:24,000, in color. John Cook (1963), P. Albert Carpenter (1970), and Jarvis Had- Blake, D.E., Phillips, C.M., and O Shaughnessy, T.B, Clark, T.W., 2003b, ley (1973, 1974), and then Stewart Farrar (1985b) and Bill Hoff- Manuscript geologic map of the Grissom 7.5-minute quadrangle, North Carolina: North Carolina Geological Survey, scale 1:24,000. man and Patricia Gallagher (1989). More recently, Rick Wooten Blake, D.E., Wooten, R.M., Parnell, D.B., Robitaille, K.R., and Pesicek, J.D., and David Parnell (Parnell et al., 2006b) and Kenny Robitaille 2007, Ductile-brittle extensional deformation along the northern Deep (2004) mapped in the Oxford-Wilton area for the North Carolina River rift basin termination in the northeastern North Carolina Piedmont: Geological Society of America Abstracts with Programs, v. 39, no. 2, Geological Survey, while Horton et al. (1992, 1994) provided p. 12–13. additional mapping coverage in the Creedmoor-Bayleaf area. We Blake, D.E., Schronce, A.G., Smith, B.C., and Kendall, J.M., 2009, Manuscript geo- thank them all for fi eld discussions concerning the geology of the logic map of the Stem 7.5-minute Quadrangle, Granville County, North Caro- lina: North Carolina Geological Survey, scale 1:24,000, in color. fi eld trip area. We would also like to acknowledge Ben Grosser, Blake, D.E., Buford, C.L., Schronce, A.G., and Hill, D.T., 2010, Geologic map Chris Buford, Adam Schronce, Tucker Hill, Brett Smith, Jacob of the North Carolina portion of the John H. Kerr Dam 7.5-minute quad- Kendall, Dan Rhodes, and Robby Morrow, UNCW graduate and rangle, Warren and Vance Counties, North Carolina: North Carolina Geo- logical Survey Open-fi le Report 2010-01, scale 1:24,000, in color. undergraduate students, and Sarah Reising Beers, NCSU under- Bobyarchick, A.R., 1981, The Eastern Piedmont fault system and its relation- graduate student, for assisting in our original mapping efforts. ship to Alleghanian tectonics in the southern Appalachians: The Journal Geologic mapping activities were funded in part by the USGS of Geology, v. 89, p. 335–347, doi:10.1086/628595. Bobyarchick, A.R., 1988, Location and geometry of Alleghanian dispersal-related National Cooperative Geologic Mapping Program, under the strike-slip faults in the southern Appalachians: Geology, v. 16, p. 915–919, STATEMAP and EDMAP programs. Michael Medina, North doi:10.1130/0091-7613(1988)016<0915:LAGOAD>2.3.CO;2. Buford, C.L., Blake, D.E., and Stoddard, E.F., 2007, Manuscript geologic map of Carolina Geological Survey drafted the base maps for the indi- the Middleburg 7.5-minute Quadrangle, Vance and Warren Counties, North vidual fi eld trip stops. Carolina: North Carolina Geological Survey, scale 1:24,000, in color. Butler, J.R., and Horton, J.W., Jr., 1995, The Buggs Island granite pluton, emplacement related to right-lateral faulting in the eastern Piedmont, Vir- REFERENCES CITED ginia and North Carolina: Geological Society of America Abstracts with Programs, v. 27, no. 2, p. 39. Bain, G.L., and Harvey, B.W., 1977, Field guide to the geology of the Durham Butler, J.R., and Secor, D.T., Jr., 1991, The central Piedmont, in Horton, J.W., Triassic basin: Carolina Geological Society Field Trip Guidebook, 41 p. 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