Paleomagnetism of some mafic intrusions in the South Carolina Piedmont. I. Magnetic systems with single characteristic directions

Abstract

Four mafic and two dioritic igneous bodies intruding along the flanks of the Charlotte belt, within the King's Mountain belt and near the Slate-Kiokee-Charlotte belt boundaries in the South Carolina Piedmont, were studied paleomagnetically. The results suggest that these mafic rocks with a single characteristic magnetization are broadly contemporaneous. A mean paleomagnetic pole position of 38.9°N 120.8°E has been calculated for the six bodies. This pole position falls near the 300 Ma old point of Irving's apparent polar wander path (APWP) for North America. The α95 circle of confidence (10.2°) includes points on the APWP between 250–360 Ma. Anomalously old KAr apparent ages, greater than one billion years, are suggestive of excess 40Ar contamination for the mafic Buffalo pluton, whereas apparent ages in the range of 360–395 Ma old are interpreted as a maximum age for the other bodies, due to the possibility of small amounts of excess 40Ar being present. A 10° westerly tilt correction suggested by Dooley and Smith for early Mesozoic diabase brings the mafic pole position of this study to more nearly coincide with the 350 Ma virtual geomagnetic position of Irving's curve, but the test is inconclusive, awaiting better definition of radiometric ages. The simplest interpretation of the data is that the mafic pole position reflects the direction of the geomagnetic field in late Devonian Carboniferous times. The similarity of this pole position with the points on the APWP for North America provides little evidence for displaced terrains and, with the precision of this pole position, horizontal displacements on the order of that suggested by the Consortium for Continental Reflection Profile (COCORP) results, or by subsequent studies, are not detectable. This and other pole positions from granitic rocks in the southern Appalachian orogen suggest that if displaced terrains exist, the evidence must be found in older rocks, or in other geologic belts.