Constraints on Alleghanian vertical displacements in the southern Appalachian Piedmont, based on aluminum-in-hornblende barometry

Abstract

Aluminum-in-hornblende barometry of Alleghanian granitoid plutons in the southern Appalachian Piedmont provides new constraints on synorogenic, vertical crustal displacements. Systematic differences in depths of emplacement between plutons in the Carolina slate belt and the Charlotte and Kings Mountain belts appear to confirm previously proposed Alleghanian folding of earlier isothermal surfaces. The Kiokee and Raleigh belts represent ductile horsts that have undergone as much as 18.5 and 15.1 km, respectively, or normal displacement along boundary faults prior to late Allegbanian dextral shearing. Plutons in or near the Eastern slate and Belair belts were emplaced at depths similar to those in the Carolina slate belt. Plutons partly or completely covered by Atlantic Coastal Plain sediments, however, appear to have been emplaced deeper and earlier, perhaps reflecting uplift prior to Alleghanian time. Geothermal gradients for the various lithotectonic belts estimated from these data are consistent with the previously recognized decrease in Alleghanian metamorphic overprinting away from the Kiokee-Raleigh belt thermal axis.