TERRANE RELATIONSHIPS ACROSS THE TAR RIVER AREA, FRANKLIN AND GRANVILLE COUNTIES, EASTERN PIEDMONT OF NORTH CAROLINA

USGS EDMAP mapping at the 1:24,000-scale has led to a refinement in understanding of protoliths and of lithodemic and terrane boundary relationships in the south-central Henderson 100K sheet. The Tar River area lies on the western flank of the Raleigh metamorphic belt and contains from west to east, the Carolina, Crabtree, and Raleigh terranes. These volcanogenic terranes record the development of a Late Proterozoic to Cambrian oceanic island-arc and its overprint by Alleghanian orogenesis and Mesozoic rifting.

The Carolina terrane primarily exposes a metamorphosed biotite quartz diorite. This greenschist facies pluton contains a variety of relict igneous features including greenstone, metagabbro, and meta-ultramafic blocks similar to the amphibolite facies Falls Lake terrane exposed just south of the study area. The Carolina terrane is also locally phyllonitic to mylonitic. One predominant dextral mylonite zone strikes 035° and defines the eastern boundary of this terrane. The Mesozoic Jonesboro normal fault has the same strike and overprints the ductile mylonite zone. This brittle fault creates a metamorphic discontinuity between the Carolina terrane and the amphibolite facies Crabtree and Raleigh terranes.

The Crabtree terrane contains white mica schist and gneiss and is interpreted to have a felsic sedimentary or volcanic protolith. The Raleigh terrane contains a complex assemblage of metamorphosed ultramafic to felsic intrusions. The Alleghanian Nutbush Creek fault zone strikes 015°-020° and juxtaposes the Crabtree terrane against the Raleigh terrane. Along this fault zone, L>S mylonite and locally phyllonite preserve dextral kinematic indicators. The Falls Leucogneiss is an L-tectonite that marks the fault zone and the Crabtree/Raleigh terrane boundary to the south, but intrudes into the Raleigh terrane east of this boundary in the Tar River area. Thus, the Falls Leucogneiss is a fundamental intrusive unit of the Raleigh terrane. The late Paleozoic Wilton pluton intrudes the Crabtree and Raleigh terranes and is truncated by the Jonesboro normal fault. Jurassic diabase dikes crosscut all units and are related to the Mesozoic rifting of Pangea.