26-6 Evaluating the Geology and Geochronology of the McLeansville Quadrangle: Bedrock Mapping, Geochemical Analyses, and U/Pb Age-Dating in the Greensboro 100K

Session: Geologic Maps, Geophysical Maps, 3-D Geologic Models, Digital Mapping Techniques, Map Derivatives, and Digital Map preparation (Posters)

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Abstract:

This study presents a geologic map of the McLeansville quadrangle, contributing to a comprehensive map of the Greensboro 100k map, which will be used by the North Carolina Geological Survey (NCGS) in future compilation efforts supporting the USGS Geoframework Initiative. The McLeansville area is currently mapped as Carolina terrane that has been heavily intruded by the Greensboro Intrusive Suite, and reconnaissance mapping indicates an ultramafic body in the northwestern part of the quadrangle. This work evaluates whether host-rock lithologies are dominantly low- or high-grade metamorphic assemblages to assess assignment to the Carolina or Charlotte terrane. Secondary objectives include documenting evidence of shear strain in the bedrock and analyzing the petrology and geochemistry of the ultramafic body to assess the possibility of a suture zone between the Charlotte and Carolina terranes.

The McLeansville area, along with parts of the adjacent Greensboro region, provides an excellent setting to explore the geologic history of island arc accretion to Laurentia during the assembly of the Appalachian Mountains. Understanding these processes is essential for characterizing the region’s primary rock types and deformation, with implications for mineral resource exploration. Field investigations were conducted in the McLeansville quadrangle to identify major lithologic units and structural fabrics, and oriented samples were collected for laboratory analyses to better interpret the original geologic conditions and processes.

Field mapping and petrographic and geochemical analyses indicate that most mapped lithologies are consistent with established characteristics of the Carolina terrane. However, outcrops within the ultramafic body contain coarse amphibole assemblages resembling amphibolite-facies rocks typical of the Charlotte terrane. Geochemical results indicate pseudomorphic replacement of pyroxene by amphibole within the ultramafic unit. The Greensboro Intrusive Suite dominates the quadrangle and includes both mafic/intermediate and felsic lithologies. Field relations suggest that the intermediate-to-mafic phase predates emplacement of the more voluminous felsic phase, which is characterized by quartz- and feldspar-rich compositions. Foliation is observed exclusively within a single lithologic unit, interpreted on the basis of field relationships and geochronologic data to represent the Hyco Formation, providing constraints on the timing and localization of deformation within the study area.

These results refine lithologic, temporal, and structural relationships within the Greensboro Intrusive Suite and improve constraints on terrane boundaries and tectonic evolution in the central Piedmont of the southern Appalachians.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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