GEOCHEMISTRY OF CAROLINA TERRANE METAVOLCANICS AND ASSOCIATED INTRUSIVE ROCKS OF THE RED HILL AND EDGEFIELD 7.5-MINUTE QUADRANGLES, EDGEFIELD COUNTY, SOUTH CAROLINA

The Carolina terrane (Ct) in South Carolina’s eastern Piedmont consist of greenschist facies, NeoProterozoic–-Cambrian metavolcanic and metasedimentary rocks intruded by epizonal plutons. Recent STATEMAP-supported geologic mapping of Ct rocks in Edgefield County, SC was supplemented by whole-rock, major- and trace-element analyses. Geochemical results are presented for (1) Persimmon Fork formation (PFf) metavolcanics, (2) a tonalite stock that crosscuts the PFf contact with the Emory formation, (3) the Edgefield granite (Eg, 317 My), (4) the lineated Johnston leucogranite (Jlg), and (5) a pink alkali feldspar granite that occurs locally within the larger, map-scale Jlg. Both the Eg and Jlg occur within the late Paleozoic Modoc shear zone (MSZ), which marks the boundary between the Ct and higher-grade amphibolite facies of the Savannah River terrane to the south.

PFf metavolcanics plot along curvilinear Harker diagram trends like those found by Shervais et al. (1996) for PFf metavolcanics to the NE and support fractional crystallization as the dominant control factor for magma evolution. Although PFf metavolcanics and the Eg have similar REE trends (La/Lu = 3-6x and 7x chondrite, respectively), crisscrossing REE patterns indicate a different source magma for these rock units as expected given that they are of different ages.

The tonalite stock and alkali feldspar granite share distinct REE signatures that have relatively higher La/Lu values (14-22x chondrite) and lower LREE and HREE concentrations (31-41x La/chondrite, 2x Lu/chondrite, respectively) than other metaigneous samples, suggesting that these two units likely fractionated from the same source rock and are similar in age.

Significant enrichment of LREEs in the Jlg (258x La/chondrite) is likely caused by mobilization of less compatible trace elements during Alleghanian deformation. Comparable HREE and HFSE concentrations in the Jlg and the Eg may indicate a shared magma source for these two granites. The relatively undeformed Edgefield granite, however, may be slightly younger than the Jlg, which is interpreted as a synkinematic intrusion within the MSZ.