Ultramafites in the Piedmont of North Carolina and South Carolina occur mainly in four types of bodies. (1) In many parts of the Inner Piedmont, small pods and lenses of Alpine-type altered dunite and peridotite are typically less than 200 m long, and their emplacement predates the main regional deformation and metamorphism. (2) In the south-central Inner Piedmont of South Carolina, more than 100 bodies of potassic ultramafic rocks occur in an area of several hundred square kilometers; the bodies are probably metamorphosed lamproites. (3) In the western Charlotte and Kings Mountain belts, peridotite, clinopyroxenite, and hornblende-bearing ultramafites are gradational into gabbroic rocks in large complexes that extend over tens of square kilometers; the ultramafites are probably cumulates formed in the roots of a calc-alkaline magmatic arc. (4) Several occurrences of ultramafic and related rocks interpreted to be dismembered ophiolites or ophiolitic mélanges are located near the Inner Piedmont–Kings Mountain belt boundary, on the flanks of the Raleigh belt, and in the Kiokee belt.

The Hammett Grove Meta-igneous Suite, here named formally, is composed of altered ultramafite (soapstone and serpentinite), metapyroxenite, metagabbro, and metabasalt lithodemes. It is interpreted to represent a dismembered ophiolite that may have formed as fore-arc basement to the Carolina arc terrane. This amphibolite-facies and retrograde greenschist-facies suite of metamorphosed, comagmatic igneous rocks crops out in the Piedmont of northwestern South Carolina near the eastern edge of the Inner Piedmont belt. The northeasternmost part of the suite lies within the Kings Mountain shear zone, which constitutes the Inner Piedmont belt-Kings Mountain belt boundary. The suite is interpreted as a thrust slice or klippe derived from the Kings Mountain belt, implying that the boundary is—at least in part—an overthrust. As ophiolites occurring in ancient orogenic terranes are often related to fundamental boundary tectonics, it is proposed that the Inner Piedmont-Kings Mountain belt boundary represents a terrane suture and marks an accretionary event. Thrusting of the Hammett Grove Suite over rocks of the Inner Piedmont resulted either from orthogonal terrane accretion or from transpression related to wrench faulting.

Abstract This publication consists of 5 chapters and resulted from the need to incorporate most of the COCORP southern Appalachian seismic reflection data and interpretations into a single work. Presented are ideas and models which are not only internally consistent, but also are consistent with what is known about the major geological and geophysical features.