A NEW COMPILATION OF THE CAROLINA TERRANE IN SOUTH CAROLINA

The South Carolina Geological Survey (SCGS) is producing a new statewide map compilation of the Carolina terrane (Ct) across central SC. The Ct contains polydeformed greenschist facies NeoProterozoic–Cambrian metavolcanic and metasedimentary rocks that are intruded by mid- to late Paleozoic plutons and are crosscut by Paleozoic ductile shear zones and brittle faults of the eastern Piedmont fault system (EPFS). The Ct was chosen for compilation because of its economic significance as a regional gold producer and as a potential source of critical minerals, its position within the I-20 growth corridor, and because the EPFS is a local source of low magnitude (<M4.2) earthquakes.

In SC, the Ct is mapped across 66 7.5-minute quadrangles. The compilation includes data from over 23 different map authors over 7 decades; contributors include SCGS, USGS, academic, and economic geologists. Published 1:24K maps encompass 38 quadrangles. Unpublished 1:24K and reconnaissance maps make up the remaining 28 quadrangles. The most detailed of these maps are graduate thesis projects and the rest contain only an assortment of point, line, and polygon data, all of which will need to be field checked for accuracy.

Edge-matching is a challenge even where adjacent maps are drawn by the same geologist. Older maps employ a lithodemic approach to their map unit descriptions, whereas more recent maps adhere loosely to an evolving lithostratigraphic framework. Other discrepancies occur when adjacent mappers lump and split map units differently. To build this compilation, map units are colored using their bulk composition and are lumped into Formations based on the currently accepted lithostratigraphy, their structural position, and where they do not fit the scale of the map.

Data quality varies significantly for each quadrangle; for example, point data density ranged from 10 – 2500 observations per map. Data density is highest in quadrangles located along the Haile-Ridgeway-Brewer gold trend. New Earth MRI funded mapping in this part of SC is providing new context to the regional geologic framework. NCGMP STATEMAP funded work is focused along the I-20 corridor between Columbia, SC and GA, providing information for earthquake hazard and development. Additional work is needed in the SW part of the terrane where detailed mapping is sparse.