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GEOLOGY OF THE WESTERN PART OF THE CAROLINA TERRANE IN NORTHWESTERN SOUTH CAROLINA mineral assemblages indicate pervasive metamorphism under amphibolite facies conditions. There is considerable evidence for ductile deformation. The last major event, emplacement of the swarm of pegmatites must have taken place while temperatures were still high. At this outcrop, we are probably looking at the midcrustal underpinnings of the Charlotte belt magmatic arc. The next three field trip stops are very close together (Fig. 8), and illustrate the coeval magmatism, deformation, and metamorphism that distinguished the Carolina terrane in the latest Precambrian through early Cambrian (Dennis and Wright, 1993, 1996). All the events recorded here occurred on the fringes of Gondwana. Dennis and Shervais (1995) and Dennis (1995) discuss these events in the context of a tectonic model presented by Nance and Murphy (1994). STOP 5: MAFIC METAVOLCANIC ROCKS OF CAROLINA TERRANE INTRUDED BY FOLI- ATED BIOTITE PORPHYRY GRANODIORITE, MCCLURE CREEK LOCATION The outcrops are located on McClure Creek approximately 200 m northwest of (behind) log home on Lancaster Road. Lancaster Road is off S-42-12, 0.5 mile north of the intersection of S-42-12 with S-42-23. (Fig. 9, Glenn Springs quadrangle) DESCRIPTION Here are observed mafic to intermediate metavolcanic rocks that are intruded by a biotite porphyry granodiorite. Volcanic rocks show porphyritic and amygdaloidal textures, and appear highly strained (Fig. 10). The contact with the granodiorite is gently dipping and near the water level in McClure Creek. The granodiorite is characterized by biotite clots that define a crude lineation and have dimensions approximately 2 cm x 1 cm x 2 mm. The granodiorite has a strong, almost gneissic fabric that parallels that in the mafic metavolcanic rock. Petrographic examination indicates that this is a composite planar fabric (so-called “S-C”) and that the granodiorite (and its country rock) have been ductilely sheared (Fig. 11). It is suggested here that the granodiorite is intruded into a locally significant dextral shear zone (of late Precambrian-early Cambrian age) based on the asymmetric tear-drop shape of the pluton and the sudden “hard-right” turn (at the map scale) of the foliation as it enters the pluton. Foliations strike northerly to north and slightly west. Dips are steep (>70°) and to the west. This is typical for rocks of the Carolina terrane in this area. The thin foliation 9
Allen J. Dennis and Others Fig. 10. Amygdaloidal greenstone on McClure Creek, Stop 5. Note subvertical foliation. Fig. 11. Photomicrograph of foliated biotite porphyry granodiorite, Stop 5. Note rounded plagioclase porphyryclast wrapped in biotite. Aggregates of biotite flakes elsewhere in this pluton define a composite planar fabric that is subvertical in orientation. Field of view approximately 25 mm. or cleavage observed mesoscopically on weathered rock surfaces is also typical. In thin section or on some fresh surfaces in hand specimen, it may be seen that the mafic metavolcanic rocks have been completely recrystallized with the growth of relatively coarse, idioblastic amphiboles, and finegrained, equant, polygonal grains making up the felsic phases. The origin of this recrystallization is obscure. Dennis and Shervais (1995) present geochemistry for an amphibolite at this site (their “McClure Porphyry”) that is an andesite. Dennis and Shervais (1995) report an ankaramite Fig. 12. Foliated xenolith in undeformed, unmetamorphosed diorite, Stop 6. Foliation orientation is at a high angle to the contact, and is consistent with orientations of foliation outside the pluton. Fig. 13. Equant mafic enclave within undeformed, unmetamorphosed diorite, Stop 6. 10
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PETROGRAPHIC AND GEOCHEMICAL STUDY
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