Neoproterozoic arc terranes of the eastern Piedmont of South Carolina and Georgia and their...

7/27/2019 Neoproterozoic arc terranes of the eastern Piedmont of South Carolina and Georgia and their Alleghanian tectonothermal overprint

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Neoproterozoic Arc Terranes of the Ea s te r n Piedmont of South Car o lina andG eorgia , and Their Alleghanian Tectonothe r mal OverprintAllen J . Dennis ' and Donald T Secor; Jr. 2

I Depar tment of Biology and Geology, Unluerslty of Southarolina -Alken , Aiken , SC 29801 -6309

De portm ent oj GeologIca l Sciences , Unluerslty of Sout hCaro lina , Co lumbia , SC 29208

IntroductionII", rt'cognilion o f deformed Carboniferous granit

tlld IlIlhe as t rn Piedmont of the Carolinas (e.g. ," ,u,k., .'1 01 , 1980) ca ta lyzed field and laboratory

III,lil'S for 111


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SALUDASYNCLINORIUM

Klok.. bettupper a m p h J b o t ~ efacies ,Alleghanian-remobilized

Late Proterozoic (ca 615-620 Ma)volcanic arc rocks.

Virgilina sequence In NC-VA.PBF and ORB Ims

Belair bengreenschist facies ,

Lale Proterozoic (ca 615-620 Ma)vo lcan ic and volcaniclastic rocks .

Virgilina sequence In NC-VA.PBF and ORB Ims

Belvedere beltschist and grlEliss co t by

Carbonilerou sGranileville granite

Crackemeck MVC

DAB MICuppetgr oonschlst 10 amphibolite lacles

mal k: metalIOIcanic rock, ..Kiokee bel l and Belair be lt protolith

traniIoOCIOO bV obHqoo slip dexlrallhrustPBF MlC

amphibolite 10 9ranotne tacir.lmelalgneou$ rocks ..ersimmon

Fork Fm, ~ " '' ' ' ' : ' ' ' ' ' I~ ; v : ' ' '/J \I , very low grade

,_ ' .... :.J''--. 5 5 O = ~ : : : " - = F m..

' I . ~v , t k 7 ~ ~ " - _ ~ ~=" " " " " ' .m

K okee bell end 8el8. bell protolilh

- rro Yr - " ' ' ' : : ! : > ' ' : ? ~ ~ 9Age of Kiokee monazite in sill schist .. 308.1 j: 2 .1 Ma, ~ 7 ~ ~- S 9/Age 01 undelOfmed Clarks Hill granite '" 3 12.0 j: 3. 1 Ma, ~ I ' L~ : . . . J- ~ & . _ "6 q

Pray, 1993: implicatiOfls lor ' weak lower crust ' models ' ./ 1'\ 6 Te

Formation of Kiokee Amiform mustpostdate youngest folded Modoc zone

orthogneiss, i.e . ca. 300 Ma

03lhrust .Ascauga fault

aeromag lineament01 EPFS~ - -- -- - - ' - - - - - -

to km

\

: : ~ : !-

Figure 2. Interpr e tive c ross -section approximately along the Savan nah River from the Carolina slate belt to theTria ssic Dunbarton basin underlying the Sauannah River Site. Adapted from Denn is, 2002.

UnconI(lnT1ilybetween CrllCkemad< and DAB ..unconformity between Virgilina and Albemarle lOch

as doscnbEld by Ha rris and GIoV9r in AamS8lR. NC arlta .

Recent field and geochronological studies havesought to discern the character and history of notonly the low grade rocks south of the Mod oc zoneand Augusta fault, but also the protoliths of amphibolite and granulite facies rocks south of theModoc zone and beneath the coasta l plain cover tothe Dunbarton basin (Figures 1 and 2; e.g., Pray ,1993 , 1997 , Dennis e t 01. , 2004). One surprisingresult of these recent studies has been the widespread recognition of ca . 620-630 Ma protolithages south of the Modo c zone. Pray (1993) reported an upper intercept age for the Clarks Hillorthogne iss from five fractions of zircon of ca. 62 6Ma. Pray (1997) reported a revised (upper intercept) U -Pb age of the Clarks Hill orthogneiss o f61 6 22 Ma. Pray (1997) additionally reportedan upper intercept age of 62 4 35 Ma for theResseau 's Crossroads orthogneiss (in the Ucheeterrane) west of Lake Sinclair , GA. Dennis et 01.(2004) reported U-Pb zircon ages for DRB-1 metadiorite of the Deep Rock Metaigneous Comp lex of

61 9 3. 4 Ma and 626.1 4. 4 Ma for the PBF -7Metaplutonic Suite. These plutonic rocks form part

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Herelh;s IIncon!(lnT1ity Is reactiva ted as II Tr subbasin border 1 I1I1Ias shewn In langlomera te r lCOV9too lrom GeB ;!

of the crysta lline basement that underlies the U.S.Department of Energy (USDOE) Savannah Rive rSite , and the ages were all determined by "conventional " Th ermal Ionization Mass Spectrometry(TIMS). Heatherington and Mueller (2005) andMueller et 01. (2005) reported a SHRIMP-RG ageof 62 3 7 Ma for the Moffits Mill Schist in theUchee belt. While much work remains to be done ,preliminary data suggest that the Uchee terraneand Kiokee belt (and, by extens ion , terranes southof the Modoc zone in SC and adjacent GA) represent a Hyco, NC - equ ivalent basement emp lacedduring dextral -normal oblique slip a long the Modoczone. This basement was th en variably remobilizedin the Late Pennsylvanian as r eco rded by numerous4 Arj3 9Ar studies (e.g ., Mah e r e t 01. , 1994 ; Rodenet 01. , 2002). We hypothesize tha t the Modoc zonecrustal scale norm a l fault ma y have bee n localizedalong an ancient suture or terrane bo undary basedon a possibl e accreti onary prism - mantle wedgeorigin for th e Burks M ounta in ultrama fic igneous

complex.

Thus, preliminary data suggest that it is possibleto interpret rocks south of the Modoc zone as correlative with Hyco -eqUivalent rocks (e.g. , Wortmanet 01. , 2000) that are well-expose d in the NorthCarolina s late belt. Relationships south of the Modoc zone along the Georgia-South Carolina borderand west into middle Georgia are comp licated byfaulting. Between the Carolina slate belt and theDunbarton basin along the Savannah River , at leastfour faults separate six metavolcanic terranes. Asdiscussed above , the Kioke e belt is framed to thenorth and south by the Modoc zone and the Au-gusta fault. The southern contact of the Belair beltis defined by an aeromagnetic lineament termedthe Ascauga fault by Dennis et 01. (2000 , 2004).South of the Ascauga fault is the Belveder e "belt ,"exposed only in rar e erosiona l windows throughCretaceous (7) - Teritary coastal plain sediments.This terrane is dominated by the undated Graniteville pluton, and the pluton's extent is determinedthrough gravity mapping and verified by well and

core data (DenniS et 01. , 2000 , 2004). While s illimanite schists have been recognized in the north -

~ I Soc/ty 0/ Am e rtca S!;; . Annual Meet!ng ~ Southeastern $ee tlon ~ Savannah. GeorgIa ~ 2007

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westernmost e ros iona l windows, south of thepluton very low grade me tavo lca nic rocks (Crackerneck Metavolcanic Co mplex) have been recov-ered; it is probabl e that ano the r Paleozoic mylonitezone separating high -grad e and low-grad e rocks iscut by the Graniteville , SC, plut on , but w e have notrecognized this. Dennis e t al. (2004) r ecognizedtwo basement terranes south of a large V-shaped

aeromagnetic lineament and identified th ese as theDeep Rock Metaigneous Complex and the PenBranch Metaigneous Complex. Th e large northeast-trending aeromagnetic lineament comprisesthe overturned Tinker Creek nappe limb withinthe Deep Rock Metaigneous Complex. Mylonitesrecovered from core penetrating this overturnednappe limb indicate hangingwall up and dextralmotion. Rocks within the wedge of the Y definedby the aeromagnetic lineament are lithologicallyidentical to the Deep Rock Metaigneous Complexbut fabri c elements (e.g. , fold axes) have been rotat ed steeply. Rocks of the Pen Branch Metaigneo us Co mp lex are emplaced above the Deep RockMeta igneo us Complex by a mylonite zone calledthe Four Mile Bran ch fault; a reactivation of thisstructure offs e ts Tertiary sediments. The Dunbarto n bas in border fault cuts the Four Mile Branchfault and Tinker Creek nappe limb at a high angie, and was itself reactivated by the Tertiary PenBranch fault (Snipes et aI., 1993). While we knowa g rea t deal about the basement structure fromthe co re we have studied, our knowledge is greatly

enh a nced by Bill Domoracki 's (1995) reprocessing of seismic lines. This work demonstrated thatstructures identified as the Ascauga fault , UpperThree Runs fault, and Tinker Creek nappe limbroot into a subhorizontal Augusta fault between 6-9 km depth.

It is likely that there are several assemblages of rocksin this area that are younger than the ca. 62 0 -63 0Ma package south of the Modoc zone. The Be-lair belt seems to have more geochemical similarities to rocks of the Carolina slate belt (Sh e rva is e t

a 1.,1996) than the basement terran es und e rlying

the Savannah River Site . Sh ervais et al. (1996)suggested a stronger affinity with the Richtex Formation than with the Persimmon Fork Formation.Stratigraphically there is little comparison betweenthe slate belt and the Belair b e lt. The possible identification of an Ediacaran fossil fragment (Maher etaI. , 1981; B. Bland , personal communication) recovered within the intermediate tuff and metasedi

mentary unit of the Belair belt (Maher , 1979) extends the possible equivalence with the Richtex.Pteridinium (Gibson et aI. , 1984) and Aspidella(Hibbard et aI., 2006) are reported from the RoydChurch and Cid Formations , respectively , of theAlbemarle Group. The Albemarle Group stratigraphy and lithology are broadly similar to the Richtexand Emory Formations of the South Carolina slatebelt. The Crackerneck Metavolcanic Complex beneath the Savannah River Site may be equivalentto the Persimmon Fork / Uwharrie Formations andLincolnton metadacite (DenniS et af ., 2004); it iscomprised of felsic to intermediate tuffs. We haveno isotopiC ages for the Crackerneck however. TheCrackerneck is of a significantly lower metamorphic grade than the Deep Rock/Pen Branch Me-taigneous Complexes , and does not contain fabricelements observed in the ca . 620-630 terranes.Dennis et af. (2004) suggested that the contact between the Crackerneck Metavolcanic Complex andDeep Rock Metaigneous Complex was equivalentto the angular unconformity between the Uwharrie Formation and underlying Virgilina sequence in

North Carolina (Harris and Glover, 1988).

Overview of Field StopsThis trip allows participants to revisit several stopsfrom the 1987 Carolina Geological Society FieldTrip, with the addition of several stops that werenot part of that trip. The time is appropriate torevisit these stops in light of the accumulation ofmore recent geochemical and geochronologicalda ta from this area, and the completion of a comprehensive bedrock geologic study beneath theSavannah River Site (SRS). Specifically , we nowunderstand that rocks southeast of the Modoc zone

Geologlco l $oc le1v of Ame rI ca ~ Annua l Mee llng ~ Southto Sfern Ste llon ~ Saoonna h. Geo rg Ia ~ 2 0 0 7

comprise a variably remobilized ca. 620-630 Materrane , coeval with Virgilina district protolith ages(i.e ., the Hyco Formation) . This terrane was exhumed by dextral , normal slip along the Middle toLate Pennsylvanian Modoc zone. Within this largecrustal block , the low-grade Belair belt (also knownas the Augusta terrane , Maher et aI. , 1991) liesin the hangingwall of the Augusta fault. 4o Ar / 39 Ar

analyses indicate that mylonitization occured alongthe Augusta fault at ca. 274 Ma (Maher et aI. ,1994). As has been noted previously (e.g., Maher ,1979) , the Augusta fault is not coincident with theaeromagnetic lineament commonly labeled as theAugusta fault ; in fact , the aeromagnetic feature isthe Ascauga fault. Thus , the Belair belt is boundedby the Augusta and Ascauga faults. South of theAscauga fault lie high grade terranes underlying theUS DOE Savannah River Site. Detailed studies ofcontinuous core underlying the SRS demonstratethat the granulite facies Pen Branch MetaigneousComplex overthrusts the upper amphibolit e facies rocks of the Deep Rock M etaigneous Complex (Dennis et aI. , 2004). North of the Augustafault, rocks of the Burks Mountain ultramafic ig-neous complex may represent the deepest -seatedrocks of the ca. 620-630 Ma complex in the coreof the Kiokee antiform. The ca. 294.2 0 .9 Maundeformed , post-metamorphic Appling granite intrudes the Kiokee antiform (Heatherington,1998) ,

Three stops allow partiCipants to visit locations internal to the Modoc zone. The variably deformedorthogneiss sheets that are a primary characteristicof the Modoc zone along its length are exposed ona tributary of Stevens Creek , off SC highway 23.At Gundy Creek, the structural style of the Kiokeeantiform that deforms the oblique slip Modoc zoneis revealed. The 643A "button schist " locality (stop6) illustrates the late strike slip shear zones that reactivate the steeply dipping limbs of F3 folds, anddemonstrates the geometry of a composite planar fabric; it also offers a warning about their use

as shear strain gauges. The 643A dextral button11 3


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schist may have form ed precisely at the same timein the middle Permian as the Augusta fault zo ne,and may be an exce llen t examp le of regional sca lestra in parti tioning. Alternative ly, and as concluded by Maher et aJ. (1994) the uniform 4oAr/ 39Arwhole-rock and min e ra l plateau across the Kiokeeantiform (ca. 274 Ma) may simply indicat e that

there was no diffe rential r o tation about a horizontal axis since the time of deformation. In this case ,deformation record ed by the 643A button schistmay be older than the age of mylonitization on theAugusta fau lt.

Finally we visit a single outcrop of lower greensc hist facies Persimmon Fork Formation with anage of ca. 550 Ma at Parks Mill.

St o p 1 . Augusta fault at Martin Marietta Aggregates Quarry: Location: 33 32 ' 24.52 "N, 82 02 '17.78 "W. (Figures 3, 4 , and 5).

The purpose of this stop is to observe the Augustafau lt at its type locality. Th e southeast-dipping Au-gus ta fault juxtaposes greenschist facies metavolcanic rocks of the Belair belt in the hangingwallagainst amphibolite facies gneisses and schists ofthe Kiokee belt in th e footwa ll (Figure 2). Thus ,the Augusta fault truncates the Kiokee antiform.The northwes t qua rry benches preserve the K iokee belt schists and gneisses, and the southeastquarry benches preserve muscovite schist and anorthogneiss sheet. Augusta fault rocks are domi

nantly fine-grained quartzofe ldspathic mylonites.The mylonites are strongly fo li ated but are not we lllineated. Strain and rock type vary wide ly withinthe zone.

Reg iona l r elations imp ly that t he Augusta fault isa norma l fault. Maher (1987a) examined the var iab ly deformed granitic veins that cut across mylonitic layering and reports that the folding andshearing of these veins systematica lly indicate ahangingwall- down sense of movement. Maher etaJ. (1994) report an 4oAr j39Ar muscov ite age for

rocks from the Augusta fau lt zone at t his loca lity of274.7 0.6 Ma.

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Figure 3. Location map for Field Trip Stop 1, March 30 , 2007.

Figure 40 . Aer ial ph o tog raph 0/ tile Augus to Qua rry , circa 2003. Used with permi ssion oj Bill Lowish , Martin Mari e ttaAggregates .

GfoIogICo/ Socle ly of Ame rica _ Annual Meeting ~ Sou t heastern Sec l fon ~ 5ooonnoh. Georgia ~ 2007

,.

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Figure 4b . Aerial photograph oj the Augusta Quarry, circa 2003 . Used with permission ojBJI/

Lowlsh, Martin MariettaAggrega tes .

Figure 5. Martin Marletta Aggregates Quarry , Augus ta.GA

(left) orthogonal jointing within the mylonite , and (right) shearedgranitic ue/ns wIthin Augusta fault mylonite .

GeologIcal Soclely of America EiI5i Annual Meeting ~ Soulheoslern $eel/on ~ Saoonnah. GeorgIa ~ 2007

Chloritization and brittle faulting are widespreadthroughout the quarry , and a re thought to recordtransition from ductile to brittle cond itions lat e inthe Paleozoic movem ent history . Nearly orthogonal , nearly vertical joint sets cut the mylonitic foliation at steep ang les.

The brittle Belair fault offsets the Augusta fault my

lonites in a sinistral sense (Bramlettet

of. , 1982).The Belair fault offsets the basement -Cretaceousunconformity with reverse sense by as much as 30m.

It is important to note that , as previous ly mentioned , the trace of the Augusta fault is differentfrom the aeromagnetic lineament commonly identified as the Augusta fault on maps of the EasternPiedmont Fau lt System . This has been recognizedfor nearly 30 years (Maher , 1979) . Th e aeromagneti c lineament is identified as the Ascauga fault

in Denniset

of. (2004) and separates Belair beltrocks from the Granitevi lle granite and its countryrock (Figure 1). A single outcrop of this sillimanite-bearing country rock is expose d in an erosionalwindow through the coastal plain along AscaugaLake Road.

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Stop 2 . Belair belt in hangin g wall of Augus tafault: Loca tion: 33 31 ' 17 .2" N, 81 59 ' 58.8 "W.(Figure 3) .

At this s top , pa rticipants w ill obse rve g ree nschistfacies ma fi c me tavo lcanic rocks o f th e Bela ir be lt.Th e rocks here a re fine-gra ined interm ediate toma fi c metavo lca nic roc ks.

Roc ks of the Bela ir be lt are subdivided into fourunit s , and are, from stru ctura lly lowes t to highes tas fo ll ows: a s ilver ph yllitic meta tuff , a lowe r felsic metatuff , a n interm ediate co mp os ition m etatuffand metase dime ntary un it , and an upp er felsicmeta tuff and meta flow unit (Maher, 19 79). Th eseunits s trike northeas t, subpara llel to the A ugustafault , and ge nera lly dip less than 45 to the so utheast (Maher, 19 79). Th e !3ela ir be lt stra tigra phy isas thick as ca. 4 ,00 0 m (Mahe r, 1979) . Th e s ilverphyllite is truncate d b y t he A ugusta fau lt and rang-

es in thickness from 20 0 -1 ,00 0 m thick, and theupp e rm os t felSic metatuff i s 70 0 m thi ck; its uppe rconta ct i s neve r observe d . Thi s o utcro p is s itua tedin the interm ediate meta tuff unit ab ove the lowes tmuscovite schist unit .

Maher et 0 1. (198 1) descr ibed a poss ible tr ilobitefrag ment fro m th e inte rmed iate tuff unit n ea r thi sloca tion . More rece ntly Ben Bland (perso na l com-munic a tion to Dennis) suggeste d this foss il wasPte ridinium .

Shervais e t 0 1. (1996) rep o rted on th e geoc hemistry of th e Bela ir be lt, and co mp ared it to wha t th eyreported fo r the Persimm on Fork and Richtex Forma tio ns. Th ese roc ks a re more ma fi c than whathas been reported in mos t Pe rsimm on Fo rk Forma tion analyses , and is mo re thole iitic, with mu chlowe r K 2 0 (


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Stop 3. . ''1')('11111111" QII," ry , llllrkl. Mo unta inultramafic comp lex. I lio n: 3337' 06 .7" N8 212 ' 58 .3 "W. (Figur es 6 nd 7) .

Th e pur pose o f thi s s top is to observe km-sca lese rpentiniz ed olivine -orth opyroxe nite bloc ks in amigmatitic biotite amphi bo le g ne iss ma trix, so uthof th e Kiokee a ntif orm cres t.

Serp entinit e with a prot o lith primarily co mp ose dof o livine + ortho pyro xe ne (ha rzburgite) is c ut b ycoa rse ta lc + serp entin e ve ins. Se rpentin e derivedfrom orth op yroxe ne bastit es are quit e co mm on.Ch ro mite is prese nt as flatte ned gra ins poss iblydefining a tectonic fo liat ion in the se roc ks . Sackse t a/. (1989) d esc ribed th ese roc ks in great d eta il.Th e distinctive array o f hills visible to the so uth ofthe Clarks Hill dam is und erlain b y these mass ivese rpe ntinit es, w hich a re e nclo sed by fe lsic gneisses w ith d istin ctive rinds a long the ir contacts . Th ese rpe ntinit e co res a re e nclosed by fibrous talc-serpe ntine-act ino lite / tremo lite zones tha t ar e sur

rounded by ta lc schist or actino lite-c hlorite schistsadjacent to the qua rtzo feldspa thic g ne isse s (Sackse t a/. , 1989) . Loca lly t he se rpentinit e bodies aresilic ified. Amp hibo lites w ithin the ultr ama fic rocksof the Bu rks Mount a in co mpl ex are interpret ed t obe rod ing ites o r Ca -me taso ma tized ga bbro slb asa l ic dikes t hat intrud ed ultr ama fic rocks prio r toserpent iniza tion (Sac ks et a/. , 19 89) . Th ese roc ksalso conta in abundant epidote. Thi s interpr eta tionis dr iven by enriched CaO (18 -23% we ight %) andSr conte nts (70 0 -3 5 00 ppm) as d ete rmin ed byX-ray fluoresce nce. Th e "norm al" 12 -18 % Al

z0

3conte nt o f these rocks means that the e levatedCaO , S r conte nt of th ese roc ks cann ot be the resultof pla gioclase acc umu lation. Amphibo lites withinthe Burk s Mounta in co mpl ex that a re not found inco nta ct with the se rp entinit es a re interpr eted t o berela tively un a ltered m etagabbros.

Th e se rpentinit e massifs e xtend a long str ike aslong as 2 -5 km . Th e ultramafi c roc ks o f the BurksMounta in compl ex (BMC) may be trac ed over theKio kee an tiform crest and are exposed as a zone of

Geological Society 0/ America ~ Annual Meellng . . oulhfoJlrn Ste llan

Appffllg 7

Sava nnah . GeorgJa ~ 2007

Figure 6 . Localfon maps for FIeld Trip S lOPS 3 and 4.March 31, 2007.

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Figure 7a) Burks Mountain Serpentinite quarry view .

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talc schists. These occur along the Clark Hill la keshore near th e contac t of biotite -amphib ole g neissand migmatitic biotite amphibole gnei ss a long KegCreek and northeast along strike into South Carolina.

Sac ks et o/. (1989) offer two interpr etati ons forthe o rig in of the Burks Mountain ultramafi c com

plex. Th e interpretation depends critically on thenature o f flattened chromite grains in the serpentinized harzburgite. If the flatt ened chromite gra insformed in a mantle tectonite then th e BMC mayrepresent an op hiolite . If, inst ead, the flattenedchromite grains represent tectonic d eformation ofan ultramafic layered intru sion, the complex wouldbe interpreted to have formed in the mid to lowercontinenta l crust. Ol-Opx cumu lates can on ly format pres sures" 4-5 kb ; this is probably too deep forformation in the ocean ic crust.

If the Burks Mountain complex repre sents an oph iolitic fragment , it now occurs at th e boundary between a Neoproterozoic protolith ( ca. 62 0 Ma) agefor Kiokee belt gneisses and rocks to the southeastof the Modo c zone , and a latest Precambrian age(ca. 55 0 Ma) for Persimmon Fork slate belt ro cksnorthw es t of the Modoc zone. In North Caro lina,the boundary between ca. 62 0 Ma Hyco-AaronVirgilina rocks and ca. 55 0 Ma Uwharri e- AblemarIe Group rocks is an angular unconformity , at leastlocally (Harris and Glover , 1986) .

Figure 7b) orthopyroxene bastftes within serpentinite . In thinsect/on, orthopyroxene is rep/aced by serpentinite .

("ot'O/oylrol Soclr l)/ oj Am erIca _ Ann ua l Mee tIn g ~ Southea stern Sec rlo n ~ Sooonnah . GeorgIa ~ 2007


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Stop 4, Appling granite at Heggies Rock: Localion: 33 32' 35.37"N, 82 15' 22. 96"W. (Figures(, and 8).

AI this stop participants will observe a Permian(Irdnite intruded into the Kiokee belt.

TI\(> Appling granite is an undeformed post-metamorphic composite granitic pluton with equigranu

lar lind porphyritic facies (Nusbaum et a/., 1992)that IntnKiI'd Inlo the Kiokee belt ca. 294.2 0. 9Me (Heatherington, 1998). Most of the exposedIXMnt 01 the Appling granite is the porphyritic faeIII, and locally the abundant K-feldspar phenoCI1/III (. 35"") lire aligned In a crude flow foliation.NuIbaum f!t 0/. (1992) suggest that the mafic enclaves within the Appling granite formed either asautoliths or from a co-mingled mafic magma. Theycite compositionally identical biotites and feldsparsfrom the mafic enclaves and porphyritic facies asevidence against a xenolith/country rock origin,but also note distinctly different oxygen isotopicIlgnatures of biotite, quartz and feldspar mineralI6lpamtes from mafic enclaves and the porphyriticIlIdl's. I ililmalply these isotopic data led Nusbaum,,/ ,,/. 11992) to conclude that trachybasalt or highK h"",1t co-mingling with a granitic melt was aIIIor" likely origin. They argue that the enclavesformed by metamorphism of initially anhydrousI""fie inclusions. Heatherington (1998) reportsrN d of 0. 5 and an initial 87Sr/86S r of .70385 at2 ( ) ~Ma. These data further suggest derivation of

tl ... Appling granite from non-radiogenic crustor

111"1111" (Heatherington, 1998)

The Appling granite is one of several major undeformed Alleghanian plutons intruding the Kiokeebelt. Others are the Sparta, GA, the Meriwether(Pray. 1997; Clarks Hill granite of Pray, 1993), andthe Columbia granites. Pray (1993, 1997) reportstwo U-Pb zircon ages for the Sparta granite: 307.1 2. 0 Ma (average of two 237UP06Pb ages, 1993)and 30 9 3 Ma (personal communication, J.E.Wright, 1997). The two ages are identical within

the error limits, an d are younger than that reportedGeoiogi((ll Societ\! of America 0 ' ~ Annual Meeting ~ _ ' - -Sou/heus""" ,."" I I " "

by Pray (1993, 1997) for the Meriwether granite.The Meriwether granite yields U-Pb zircon ages of312.0 3.1 Ma (average of three 237Upo6Pb ages,1993) and 31 2 4 Ma (personal communication,J.E. Wright, 1997). Thus, the Appling granite is theyoungest known Alleghanian granite in the Kiokeebelt, and one of the youngest if not the youngest inthe southern Appalachian Piedmont. [The Siloam

granite which had a very young Rb-Sr age (Jonesand Walker, 1973), was dated by the U-Pb zirconmethod by Samson (2001) and yielded an age of30 4 + 3.5/-2.3; Pray (1997) cites a 30 7 4 Maage (personal communication, J.E. Wright) for theSiloam.] Pray (1997) reports a U-Pb zircon age forthe Columbia, SC, granites; these date to 30 8 3Ma (personal communication, J.E. Wright).

The Graniteville, SC, granite does not intrude theKiokee belt, but does intrude the composite ca.620-630 Ma terrane south of the Modoc zone.

There is no age reported for the Graniteville granite.

SOl'Clnnan. Georgia ~ - " , = '2007

Notes

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Figure 8. aJ Large mafic enclave w ithin Appling granite at Heggies Rock (above). b) Typical exposure view (below),

Stop 5. Gundy Creek parasitic fold relationshipsas a mod el for the Kiokee antiform structure. Locat ion : 3342' 21.7"N 8208' 54.1"W. (Figures9 a nd 10).

At this stop , participants will observe structuresthat inform regional scale crosssections of theeaste rnmost Piedmont of South Carolina and ad jacent Georgia.

This large outcrop was mapped by Scott Mcintyr ein the summer of 1986 for an undergraduate thesis at the University of Nebraska-Omaha (Maher ,1987b). This outcrop clearly shows the structuralstyle of the Kiokee antiform that folds the Modoczone. Outcrop scale structures show that we are onthe northwest , overturned or steep ly dipping limbof the D3 Kiokee antiform. Th ere is no me soscop icaxial planar cleavag e that accompanie s this fo lding. Thinly lamin ated Modoc zone paragneissesare folded about subhorizontal axes with steep lySE dipping axial surfaces. It is clear that what appear to be near isoclinal fold limb s on horizontalpavement surfaces are in fact an artifact of thesegently plunging axes. Folds with steeply plungingaxes with consistent dextral or clockwise rotationsense or asymmetry (reverse slip crenu lations , orRSC of Dennis and Secor, 1987 a, 1990) that d eforms steeply dipping D3 limbs represent D4 dextral strike slip deformation in this area (Dennis etaI., 1987).

Beneath the bridge that is near this stop, abundantshear bands (or normal sense crenulations, NSCof Dennis and Secor, 1987a , 1990) contain blacktourmaline prisms. These tourmaline need les arenot common but have been noted elsewhere in theModoc zone, and are associated with the paragneisseses near orthogneiss sheets. Presumably thevolume of water necessary to ca rry the amount ofboron (B) represented here greatly aided the plasticdeformation in this area as we ll as facilitating material transfer; additionally the amount of B may have

reduced the viscosity of felsic orthogneiss sheets

120 a.ologlool Soc le fy of Ame rica ~ Annual Meeting ~ Southeastern Sec llon ~ Savannah . GeorgIa ~ 2007

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Figure 9. Locatfon maps for Fi e ld Trip Stops 5 -6, March 3 1, 2007.

a nd assisted th e ir ascent through the crust. Mah ere t oJ. (1994) report ed an 4oAr/ 39 Ar muscovit e plateau age from this site of 277.7 0. 4 Ma.

Because orthogneiss sheets are folded by F3 fo ldsof th e Kiokee antiform. northw es t verging f oldingand transport must p os t-date orthogneiss em p lacement a nd Modo c zo ne shearing.

Geolog lcol Socle ly 0/ Am erica ~ Ann ual Meeti ng _ Sou lhmtll! rn 5 110" Sava nnah . Georg ia ~ 2007

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Figure 10 . a) Shallowl y plunging outcrop scale folding on the steeply dipping Ifmb of the Klokee antiform at Gundy Creek .Scale Is 120 cm . Folded Layering is Ifghtly tra ced (aboue) . b) Pa uement view of mesoscopic dextral folding D 4 (verti cal axialsurfa ce s) within pora gnelss at Gund y Creek . Pen cap point s north (abo v:e ).

Stop 6 . Button Sc hist o ff Forest Service Road64 3A. Location: 33 42 ' 13.9 "N 82 10 ' 58 .1 "W.(Figures 9 and 11) .

Here, participants will observe stra in partition ingat ca. 27 4 Ma between the Augusta fault and a latedextral strike -slip reactivation o f the Modoc zone(lrmo shea r zone).

In the Clarks Hill area, subvert ica l portions of theKio kee antiform, with fo lia tion st rikes o f ca. 065we re prefer e ntially reactivated as dextral strik e slipshea r zones. Th e re a re three map scale zones ofthi s reactivation in this area: th ey are , from n orthto sou th , the Northern Clarks Hill, Ridge Road ,a nd Gundy Creek zones (Dennis et 01., 1987).Th e o utcr ops o ff Forest Service Road 643A , SC ,an d Ridge Road on the lakeshore in GA ar e e xcept ional expos ures o f shear bands form ing in micaceous rocks . Dennis and Secor ( 1987a) ca lledthese st ructur es normal slip crenulations t o e mphasize their comp lementary relationship to stru cturesthat fo rm when th e pre -existing slipping foliationmak es an acute ang le to the slip d irectio n (i.e.,reve rse s lip cremJiations). Th ese ou tcrops s howvery clea rly the re lat io nship between a pre -ex istingslipping foliation a nd crenulations f or med duringshearing (Dennis and Secor , 19 8 7 a, b ; Dennis e ta/. , 1987). Sp e cifica lly, because fo lia tio n surfacesa re microscopi ca lly penetrat ive a nd crenulationsurfa ces are pe netrativ e on ly to the mesoscopic

sca le , slip o n foliation surfaces rota tes c ren ulat ionsurfaces , but c ren ula tion slip on ly t rans lates foliation . Thu s in foliated shear ed metape lites , with increasing s hea r stra in , the a ngle between fo lia tiona nd normal slip cre nulat ions does not decrease ,inst ead it increases. Converse ly, with increasingshea r stra in th e ang le between ax ial surfaces ofreverse slip cre nulat ions and pre-existing foliationbecomes smalle r and the fo lds become increas inglyapp resse d and intrafolial. Th e re a re numerous loca tions here where single quartz veins hav e beeno ffset by normal slip crenula tions and can be used

as strain gauges to determine th e magnitude of slip

122 O>Ioglral Socle tv 0/ AmerIca !$iiia! Annual MeetIng ~ So u theaste rn Section ~ Saoonnah. GeorgIa ~ 2007

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along cr enula tion . D nni s e t al. (198 7) used theserelationships to es lim t e y a lo ng c renulation to be,,2. More rec e ntly, these ou tcrops a nd the buttonschist at Gundy Cr ee k we re Inte rpr eted by Prayet al. (1997) to be exa m ples o f co nverge nt shear.Such a zone forms betwee n rigid bloc ks which donot rotate relative to one a nother, a nd th e shearbands (C ') form as a st eady stat e fabric e le ment

parallel to the relative ve locity vec to r be twee n thetwo converging walls.

Regionally, these late shear z o nes ar e int erestingbecause they may have been active at the sametime that norma l motion occurr ed along th e Augusta fault. Maher et al. (1994) report ed a ,oAr/39 Ar whole-rock phyllite plateau age from this siteof 274.4 1.0 Ma. In fact ,oAr/ 39Ar plateaus uniform ly yield nearly id.en tica l Permian coo ling agesacross the Kiokee foliation arch in the SavannahRiver area (Maher ' et aI. , 1994), and act ual mo

tion along these late dextral shear zones could haveoccurred ear lier. The Ar data suggest that a moreconservative interpretation may be that there hasbeen no differential motion about a horizontal axisin this area since ca . 27 4 Ma. Because these shearzones on ly occur on the steeply dipping limb s ofthe regional F3 fold , they limit th e you ngest possible age for F3 fo lding . Augusta normal faultingand Irm o shearing represent the young est ductileor possible Alleghanian Appalachian events in thisarea, and postda te crusta l shorte ning followingModoc zone oblique normal dextral slip by 20 -30Ma. They ma y represent a terminal Pangean assemb ly event in this area.

GeologIcal Socle tv of A me r Ica _ A nn u al Meelfn g .. . o u f h~ J /.. rn 5, lon

Figure 11 . Button schist pavement surfa ce oJf Forest ServI ce Road 643A, at th e Inter section of west e rn power line , andBuzza rd C reek .

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Stop 8. Stevens Creek at Plum Branch. Location:3351 ' 11.9"N 82 13 ' 34 .7 "W. (Figures 13 and14) .

Here, participants can observe the lithologies andstructural style of the ca. 55 0 Ma Persimmon ForkFormation of the Carolina slate belt.

North of th e Modoc zone , there is a dramati c de

crease in grade and ductile deformation and conco mitant preservation of primary structures. Rockso f th e Carolina slate terrane include , broadly, andes itic volcanic and epiclastic rocks. These rocksrang e in age from 55 0 Ma to Middle Cambrian.Middle Cambr ian roc ks co ntaining a diverse peri -

o ndwanan fauna (Asbill Pond Formation ; Samso n e t 01. , 1990; Secor and Snoke , 2002) occurabove an angu lar unconformity (Dennis et 01. ,1993 ; Dennis and Wright , 1997) . The siltstonesand sandsto nes beneath the angular unconformity(the Emory Formation of Secor and Snoke , 2002)a re gradat ional into the Persimmon Fork Formation (ca . 550 Ma ; e.g., Dallmeyer et 01. , 1986 ;Barke r e t 01. , 1999; Ayuso et 01. , 2005). It isthese roc ks of the Persimmon Fork Formation thatare obse rved here at Parks Mill. Thus , the angula r unco nformity preserves evidence in the easte rn Piedmont of an orogenic event at about theCa mbrian -Precambrian boundary that occurredon the periphery of Gondwana (e.g., Hibbard andSamso n, 1995 , Dennis and Wright, 1997 , Barkere t 01. , 1999). The angular unconformity is folded ,

and that fo lding is cut by a ca. 41 5 Ma pluton.Loca lly there is 4oArj39Ar evidence for a c1eavage-forming event at ca. 45 5 Ma (Noel et 01 ., 1988 ;Offield e t 01. , 1995) in the North Carolina andSouth Carolina slate belt. Furthermore paleomagnetic data indicate accretion of Carolina to Laurentia with a shared pole by Late Ordovician time(Noel e t 01. , 1988 , Vick et 01., 1987) . It is possible to see folding of bedding , or at least clast -richlayers at Parks Mill; observations of the wea theredpavement surface make clear that a cleavag e isfo lded here. It is not clear whether th ese fabric e l-

Geologlcol Socle ly 0/ Ame rica ~ Annual Meellng _ Sou/MoJ " rn s. c llar!

FIgure 14 . oj Overview of Carolina s late belt Pe rsImmon Fork Formation , Parks Mill , field trIp stop 8.

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Figure 14 . b) Tight folding of 50,,51, near vertical axia lplanes, va ria ble plunges, pavement surface .

ements are related to th e angular unco nformi ty(ca. 54 2 Ma age), the folding o f th e angu lar unco nformity (Late Ordovician) , or bot h.

South of t he Modoc zone , in the Kiokee belt , Belair be lt, and the subs urface te rrane s unde rlying th eDOE Savannah River Sit e , there is little or no evidence of these oroge nic eve nts at the CambrianPrecam brian bound ary or in the Ordovi cian. Th ereis sca nt evidence for th e S ilurian magm a tic eve ntdiscussed b y Samson and Seco r (2000) or Denni s(2006), notwith standing the ca. 421 Ma Lake Mur

ray gneiss in the Kiokee

be lt [containing xenocrystic z ircons o f ca. 44 4 and ca. 48 9 Ma age , possibly

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Figure 14 c) Vertical joint surface show in g folded 50,,51 , n .b . lapillV breccia clas ts.

reco rding recycling during the Ordovician eve nt(Samson and Secor , 2001)]. and the ca 3 78 Maage reported for the Springfield gran ite by Speer(1982). Wh ether this is the resu lt of a comp lete rese tting o f iso topic clocks by the Alleghanian eve ntin the o lder terran e , juxtaposition o f terranes withdistinct tecto noth erma l histori es by dextral normalob lique mo tion along the Modoc zone, shu ffling o fa single co mp os ite terran e by the Modoc zone , ormuch la ter (Alleghanian ?) a cc re tion of the o lder terrane dur ing climac tic Gondwa nan-Laur entian co llision is unclea r. A 620 -6 30 Ma terrane is clear lythe baseme nt to the ca . 55 0 M a sequence in North

Carolina (Harris and Glove r, 19 88). That thi s basement ma y be fault ed (along the Modoc zone) intoits current position , and that the fault juxtaposesport ions of a co mp os ite terrane with uniqu e tectonotherma l histori es may be the s impl est ex planation of the observed relat ions hips (compare toSt e ltenp ohl , 2005) . It is possible that the Modoczo ne, the locus of subcru sta l lith osp heric delamina tion interpr e ted by Sacks and Secor (1990 a,b)may b e localized along an ea rlie r plate bou ndary orsuture as suggested by mantl e tecto nites preservedwithin the Burks Mountain Igneo us Co mplex.

Gtologlcoi Socle ly of Am e rI ca S! S Ann ual Meeting ~ So u theastern Sec tion ~ Souonnoh . Georgia ~ 2007

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Hi bbard , J. , McMenamin , M. , Pollock , J. , Weaver, P , Tacker,R C. , Miller, BV , Samson , S.D. , and Secor , D.T ., 2006 ,Significa nce of a new Ediacaran foss il find in the Carolina terra neo f No rth Car o lina: Geologica l Soc iety o f America Abstracts withProg ra ms , v. p.

Hibba rd , J. P , and Samson , S.D. , 1995 , Orogenesis exot ic tothe iape tan cycle in the southern Appalachians , in Hibbard ,J. P . van Staal , c.R. , and Cawood, PA : Association of CanadaSpec ial Paper 41 , p. 191 -205 .

GeologI cal Soc le ly of Am e rI ca ~ Annual M eeJlng _ SolltlltO. t ,m Sec ti on ~ Saoonn ah . Georgia ~ 2007

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Sa mson , S. L. , Palmer , A R , Robiso n , R A , and Secor, D T,Jr ., 1990 , Biogeograph ical significance of Cambrian trilobitesfrom the Caro lina S late belt: Geological Society o f AmericaBulletin , v. !O2 , p. 1459 -1470.

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Secor, D T , and S noke , A.W., 2002 , GeologiC map of theBatesburg and Emory 7.5 ' Quad rangles , Lex ington and Richlandco unti es with ex planato ry notes: Geo logical Soc iety o f AmericaMap and Chart Series , MCH-09 1.

Secor , D.T. , J r., Snoke, A.W., Bramlett, K.W., Costello , a.p. , andKimbre ll , a. P., 1986a , Character of the Alleghanian orogeny inthe southern Appalachians: Part I. Alleghanian deformation inthe easte rn Piedmont of South Carolina: Geological Soc iety ofAmerica Bulletin , v. 97 , p. 131 9- 132 8 .

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Neoproterozoic arc terranes of the eastern Piedmont of South Carolina and Georgia and their...

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