LITHOLOGIC AND GEOCHEMICAL CORRELATIONS AMONG VIRGILINA SEQUENCE ROCKS IN THE CAROLINA TERRANE OF NORTH CAROLINA

In the north-central NC Piedmont, subduction-related greenschist facies metavolcanogenic rocks of the Hyco, Aaron, and Virgilina Formations define the Virgilina sequence in the northeastern Carolina terrane. Recent NCGS STATEMAP work in the Lake Michie and Stem 7.5-minute Quadrangles focuses upon this sequence in the Flat River Complex, interpreted to be the remnants of a volcanic pile and its subvolcanic magma chamber (McConnell and Glover, 1982). This complex contains metamorphosed crystal lithic dacite tuff, basaltic flows and dikes, and lesser amounts of dacitic volcaniclastic rocks that serve as the wallrocks to 613 Ma metamorphosed granodiorite, tonalite, and diorite plutons. A suite of 20 metaigneous samples was collected from these quadrangles and analyzed for whole-rock major and trace element abundances in order to test geochemical correlations 1) between Flat River Complex rocks and Virgilina sequence metavolcanic and metaplutonic rocks from the Oxford, Henderson, Wilton, and Townsville Quadrangles along strike to the northeast and from the Chapel Hill, Hillsborough, and Efland Quadrangles to the southwest, and 2) between Flat River Complex metavolcanic and metaplutonic rocks.

As a group, these Virgilina sequence rocks show a bimodal distribution of mafic and felsic samples on a silica histogram, and a Daly Gap for intermediate compositions. Standard Harker and AFM major element diagrams indicate the rocks form linear crystal fractionation trends and span the compositional range between tholeiitic and calc-alkaline compositions. A CaO-Na₂O-K₂O comparison diagram verifies that the Flat River Complex and its regional counterparts are part of a Na-enriched volcanic system. When plotted with regional samples, Stem and Lake Michie rocks match regional trends on tectonic discrimination diagrams, reinforcing the concept that the Flat River Complex was formed in an island-arc setting. However, several Virgilina sequence samples indicate some continental contamination is possible. In addition, preliminary REE and trace element diagram comparisons of Flat River Complex metavolcanic and metaplutonic rocks do suggest that intruding felsic granitoid plutons may be the source for the dacitic pyroclastic eruptions.