THIN THRUST SHEETS OF THE NEWBERRY, SC REGION AND THEIR GRAVITY ANOMALIES

Several major Late Paleozoic high-angle dextral strike-slip ductile shear zones and thrusts mark the boundary area between the Inner Piedmont terrane and the Carolina terrane near Newberry, SC. The relationship between the shear zones and the thrusts remains a problem of geometry and sequence. Gravity data have been collected in nineteen 7.5' quadrangles in an attempt to clarify the geometry. Within these quadrangles, the Lowndesville, Buzzards Roost, and Chappells shear zones have clear gravity expression. However, subtle to no gravity anomalies are associated with the Cross Anchor and Indian Creek thrusts. Since the Cross Anchor thrust sheet (Carolina terrane) is very thin, some gravity anomalies due to density contrasts within the thrust sheet are obscured by masses lying beneath the sheet. Within this thin sheet, the southern part of the Bald Rock batholith has virtually no anomaly. However, the Buffalo gabbro has a high density contrast and a clear anomaly that can be modeled with a body less than one km. thick, indicating that the Cross Anchor fault dips east at less than 10 degrees. Since the shear zones also cannot be modeled to great depths, they are apparently truncated at depth by thrusts. An oddity of the region is the presence of a large gravity high (15 milligals) common to the regions overlain by the Carolina terrane (Cross Anchor thrust sheet) and the Inner Piedmont terrane within the Whitmire re-entrant, suggesting that both known terranes are underlain by a large dense mass in another sheet at a comparatively shallow depth. Alternatively, it is possible that the region within the Whitmire re-entrant is not really part of the Inner Piedmont terrane.