gb 1978.book - Carolina Geological Society

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DISTRIBUTION OF CRYSTALLINE ROCKS AND THEIR RELATIONSHIP TO THE BELAIR FAULT ZONE Figure 3. Aeromagnetic map from Daniels (1974) showing proposed zones near Augusta, Georgia. Fault zones are identified as: B, Belair fault zone of Hatcher and O’Connor (in press); H, Augusta fault of Hatcher and others (1977); D, fault of Prowell and O’Connor (in press); P, extension of Augusta fault from Prowell and O’Connor (in press). STRUCTURAL GEOLOGY The southeast-dipping en echelon reverse faults that constitute the Belair fault zone extend from Fort Gordon Military Reservation northward to the Savannah River (Fig. 1). At localities where the faulting has juxtaposed crystalline and sedimentary rocks, the fault plane consistently strikes N25° - 30° E and dips 50° SE, subparallel to the cleavage in the Belair belt phyllite. Where only crystalline rocks are involved in the faulting, the fault planes are much steeper (approximately 70° - 80°). Shear zones in the crystalline rocks are as much as 8 meters (26 ft.) wide and are easily recognized by the brittle fracturing of the hard strata. Gouge zones along which major movement has taken place, are commonly filled by as much as 15 cm (6 in.) Of chlorite. The relatively steep contact (45° - 75°) between the Belair belt phyllites and the Kiokee belt gneisses (the Augusta fault, Fig. 1) is cut by the Belair fault zone, and it serves as an excellent indicator of lateral displacement. Mapping of this regional structural boundary indicates a left lateral separation of 23 km (14 miles) along the Belair fault zone. Drill-hole data and field observations have verified that the Belair fault zone forms a sharp boundary between phyllites and gneisses for most of its known length (see Fig. 2). The two rock types are separated by a crush zone about 5 meters (17 ft.) wide or less. Because the mylonitic contact between the Belair and Kiokee belts probably formed during regional metamorphism approximately 350 million years ago (Kish and others, 1978), the brittle deformation resulting in lateral displacement along the Belair fault zone must have taken place subsequent to cooling of the crystalline rocks. Whether the lateral displacement occurred before or after the deposition of Coastal Plain strata is discussed elsewhere (Prowell and O’Connor, in press). CONCLUSIONS Geologic mapping shows that the Belair fault zone is a major structural feature at the margin of the Atlantic Coastal Plain. The fault zone is composed of at least eight en echelon reverse faults and is at least 24 km (15 miles) long. Vertical displacement of the erosional unconformity between the Coastal Plain sediments and crystalline rock has been at least 30 meters (100 ft.) since the late Cretaceous. Lateral displacement of the Augusta fault by the Belair faulting indi- 39
David C. Prowell cates a horizontal displacement of approximately 23 km (145 miles) since the cooling of the crystalline rocks in the Belair and Kiokee belts and the formation of the Augusta fault mylonite. The importance of the Belair fault zone to geologists mapping crystalline rocks in the southeastern United States is that it represents post-Paleozoic faulting that dramatically altered the distribution of crystalline rocks. It also proves that postmylonitization brittle deformation is of such magnitude that it should be of major concern to Piedmont geologists. REFERENCES CITED Crickmay, G. W., 1952, Geology of the crystalline rocks of Georgia: Georgia Geological Survey Bull. 58, 56 p. Daniels, D. L., 1974, Geologic interpretation of geophysical maps, central Savannah River area, South Carolina and Georgia: U.S. Geol. Survey Geophysical Investigations Map GP-893, 3 sheets, 10 p. text. Hatcher, R. D., Jr., Howell, D. E., and Talwani, P., 1977, Eastern Piedmont fault system: Speculation of its extent: Geology, v. 5, p. 630-640. Kish, Stephen, Fullagar, P. D., Snoke, A. W., and Secor, D. T., Jr., 1978, The Kiokee belt of South Carolina: Evidence for Late Paleozoic deformation and metamorphism in the southern Appalachian Piedmont (abs.): Geol. Soc. America Abstracts with Programs, v. 10, n. 4, p. 172-173. O’Connor, B. J., and Prowell, D. C., 1976, The geology of the Belair fault zone and basement rocks of the Augusta, Georgia area: Georgia Geol. Soc. Guidebook, n. 16, p. 21-32. Prowell, D. C., and O’Connor, B. J., in press, Belair fault zone: Evidence of Tertiary fault displacement in eastern Georgia: Geology. 40
Page 2 and 3: CAROLINA GEOLOGICAL SOCIETY FIELD T
Page 4 and 5: CONTENTS CAROLINA GEOLOGICAL SOCIET
Page 7 and 8: CAROLINA GEOLOGICAL SOCIETY Guidebo
Page 9 and 10: STRUCTURE OF WEST FLANK OF THE RALE
Page 13 and 14: GEOLOGIC RESEARCH IN THE RALEIGH BE
Page 15 and 16: Van Price, Jr. and R. Bruce Ferguso
Page 17 and 18: Van Price, Jr. and R. Bruce Ferguso
Page 21 and 22: MAGNETOMETER ANOMALIES IN THE HAILE
Page 23 and 24: MAGNETOMETER ANOMALIES IN THE HAILE
Page 25 and 26: Martha Carr TABLE 1. SUMMARY OF MES
Page 27 and 28: Martha Carr Columbia, South Carolin
Page 29 and 30: Alexander W. Ritchie and Wallace C.
Page 33 and 34: PETROLOGY OF THE GREENWOOD PLUTON p
Page 35 and 36: Harmon D. Maher Figure 1. Geologic
Page 37 and 38: Harmon D. Maher Augusta fault zone
Page 39: David C. Prowell Figure 2. Contour
Page 43 and 44: Stephen A. Kish Figure 1. Distribut
Page 45 and 46: DONALD T. SECOR, JR., AND ARTHUR W.
Page 67 and 68: FIELD TRIP ITINERARY Figure 17 - A.
Page 69 and 70: FIELD TRIP ITINERARY apparently was
Page 71 and 72: FIELD TRIP ITINERARY formed during
Page 73 and 74: FIELD TRIP ITINERARY dike (Fig. 20-
Page 75 and 76: FIELD TRIP ITINERARY 149. Butler, J

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