Tectonic and geologic development of the Charlotte belt south central Virginia Piedmont

Abstract

The map area in the south central Virginia Piedmont is primarily in the Charlotte belt, but includes a portion of the adjacent Carolina slate belt. Both the Charlotte belt and the Carolina slate belt are major components of the volcanic arc, Carolinia, that collided with Laurentia during the Late Cambrian to Late Ordovician Taconic orogeny. Both belts consist primarily of volcanic rocks, the major difference being that the Charlotte belt is amphibolite grade gneisses, whereas the slate belt is at greenschist grade.

The major results of the study are as follows:

(1) The Carolina slate belt units, the Hyco Formation and the Aaron Formation, are present in the Charlotte belt, and a correlation between the two belts has been made.

(2) The Charlotte belt has a calc-alkalic index of 64, has a calc-alkaline differentiation trend, is metaluminous to peraluminous, and major and trace element discriminant analyses show that the basalts are predominantly low-K tholeiites with lesser calc-alkaline basalts. These results indicate that the Charlotte belt, like the more well-known Carolina slate belt, originated in a volcanic arc tectonic setting.

(3) The Charlotte belt has undergone four deformational events, a D₁ (Virgilina Deformation?) folding and cleavage-forming event, a D₂ (Taconic) recumbent fold nappe forming event caused by the northwest thrusting of the infrastructural Charlotte belt sequence beneath a Carolina slate belt suprastructure, a D₃ dextral shearing event (Acadian?-Alleghanian) forming the Brookneal and Clover shear zones bounding the Charlotte belt on the northwest and southeast, respectively, and a D₄ event (Alleghanian) that produced regional-scale northeast-trending open folds across the area.

(4) The Charlotte belt has experienced two metamorphic events, an M, metamorphism (Virgilina?-Taconic) up to upper amphibolite grade, and an M, metamorphism (Acadian?-Alleghanian) that shows effects only in the Brookneal (amphibolite) and Clover (greenschist) shear zones.