14-2 Distribution, Geochemistry, and Petrogenesis of the Lockhart Plutonic Suite, Charlotte Terrane (SC, USA)

Session: New Research in the Appalachian-Ouachita Orogen: Integrated studies from the Foreland to the Hinterland

Presenting Author:

Steven Mittwede

Authors:

Mittwede, Steven K.¹, Yasar, I. Dogancan², Davis, Zachary T.³, Johnson, Savanna L.⁴, Kamenov, George D.⁵, Chaumba, Jeff B.⁶

Abstract:

Carolinia (Carolina superterrane) comprises an amalgamation of exotic peri-Gondwanan terranes within the southern Appalachian orogen, and the Charlotte terrane represents the predominantly plutonic core of a subduction-modified island arc. Within the Charlotte terrane, situated in and around the town of Lockhart, South Carolina, the rocks that make up the zoned Lockhart plutonic suite (LPS) crop out over roughly 20 km² in Union and Chester counties. Oscar Lieber (1858, p. 49), one of the early state geologists, noted the occurrence of “a black, coarse hornblendic rock” at Lockhart’s Shoals but, to our knowledge, these rocks have not been the subject of modern scientific study other than reconnaissance mapping by Horton and Dicken (2001).

Recently completed fieldwork and petrographic examination reveal that the core of the LPS is weakly metamorphosed harzburgitic, pyroxenitic, and melagabbroic adcumulates and mesocumulates cut by later aplitic and pegmatitic graphic-granitic dikes and sills. Granitic to dioritic rocks, containing clear evidence of magma mingling, crop out in streams on the W and NE sides of the LPS, whereas microgabbroic rocks generally occur near some margins of the LPS. Here we present the results of new bulk-rock geochemical analysis of the ultramafic-mafic samples of the LPS. The analyzed preliminary sample set (n=7) yielded tholeiitic characteristics for these basaltic rocks that appear to have a depleted source. The LPS ultramafic-mafic samples display subduction modification ([Th/Nb]N= 2.35-23.1) through their immobile trace-element behavior and have characteristics (Ti/V= 6-15) consistent with formation above a subduction wedge within an island-arc setting. It is likely that these rocks are petrogenetically akin to the Concord Plutonic Suite exposed along strike to the northeast in central North Carolina and to the Gladesville and associated intrusive bodies to the southwest in central Georgia.

Future work will include further geochemical characterization of the full range of lithologies within the LPS, and geochronological analysis of the late-stage felsic intrusions will be integrated to constrain the timing of the formation of the LPS. A thorough understanding of the LPS will provide new insights into the tectonic evolution of the Charlotte terrane as a key component of Carolinia.

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