INTRA-ARC LITHOTECTONIC RELATIONSHIPS IN THE NORTHEASTERN CAROLINA ZONE, EASTERN PIEDMONT OF NORTH CAROLINA

Over the past twelve years, geologic mapping in the North Carolina eastern Piedmont (NCEP), under the auspices of the USGS National Cooperative Geologic Mapping Program in the Raleigh and Henderson 30X60-minute sheets, has led to a refinement in our understanding of the region’s tectonic history.

The NCEP represents an amalgamation of second-order terranes characterized by diverse metaigneous, metasedimentary, and igneous rocks, and fabrics attributed to bounding and crosscutting ductile-brittle fault strands. These features range in age from late Proterozoic to early Mesozoic. Superterrane-scale compilations group the NCEP terranes as the northeastern portion of the Carolina Zone, a first-order tectonostratigraphic element of the southern Appalachian orogen that has a peri-Gondwanan affinity. However, several of the gneiss terranes are linked as the southern extension of the Grenville Goochland terrane of south-central Virginia, which is considered to have a Laurentian affinity.

With an understanding of detailed field relationships and following petrographic analysis, 135 representative samples were selected for whole-rock geochemical analysis, in order to: 1) evaluate possible links between lithotectonic sequences from the NCEP and Carolina terrane sequences in the central Piedmont and 2) consider various tectonomagmatic origins for terrane protoliths. Major and trace element data from NCEP terranes are compatible with data from the Carolina terrane and support a subduction-related volcanic arc and potential back-arc origin for the terranes. Internal suite complexities may be related to multiple magmatic pulses and source regions, basement heterogeneities in the arc substrate, and the effects of successive episodes of alteration, metamorphism, and deformation in the Carolina Zone resulting from initial arc development and its peri-Gondwanan to peri-Laurentian transfer during the construction and eventual breakup of Pangea.