9 Evolving Perspectives on Piedmont Geology: Terrane Studies, Structural Analyses, New Mapping, and Complementary Studies (Posters)

Thursday, 31 March 2016
8:00 AM - 5:30 PM
Exhibit Hall

MAJOR TECTONIC ELEMENTS IN THE SOUTH CAROLINA WESTERN INNER PIEDMONT: KEY RELATIONSHIPS FROM CLEVELAND AND EASTERN TABLE ROCK 7.5-MINUTE QUADRANGLES

Paper number: 9-8
Program: Symposia Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

Recent re-mapping of Cleveland and eastern Table Rock quadrangles with refined map units has delineated a complex fold-fault chronology for this part of the South Carolina western Inner Piedmont. A key marker in the tectonic development sequence is the Seneca ductile fault at the base of the Six Mile thrust sheet (Poor Mountain and Tallulah Falls formations). Middle Ordovician quartzo-feldspathic gneisses of the Walhalla thrust sheet lie in the footwall. Brittle faulting and deep erosion have modified the original continuity of all structures.

The oldest macro-scale tectonic element (TE-1) is two systems of NW- and SW-vergent, overturned folds (F1 and F2) affecting Six Mile rocks. TE-2 involves inclined, N-NE striking folds (F3) also affecting these rocks. The Seneca ductile fault (TE-3), emplaced northwestward, currently truncates the traces of earlier folds. NW- to SW-vergent, inclined-overturned F4 folds (TE-4) deform the Seneca fault and all hanging wall-footwall rocks, producing structural windows in the Six Mile sheet. F4 is contemporaneous with emplacement of the Eastatoee ductile fault (TE-5). Collectively, TE-6 is the development of a Type-1 interference pattern of broad folds of NE- and NW-strike (F5 and F6). Significant is Six Mile rocks preserved in synformal downwarps of both strikes, flanked by footwall-cored antiforms. South-directed compression has thrust Walhalla gneisses southward back over Six Mile rocks and F4folds along E-W greenschist-grade shear zones (TE-7).

All earlier macro-scale fold patterns (F1–F6) were disrupted and rearranged by sets of NW-, N-, NE-, and E–W-striking oblique-slip to dip-slip faults and NE-striking cataclastic zones, collectively TE-8. Riedel relationships exist among these faults. Major dextral and sinistral, ~E–W-striking fault zones of TE-8 have 2-6 km of strike-parallel offsets, merging eastward with regional NE-striking faults. Widespread TE-8 Inner Piedmont oblique-slip to dip-slip normal faults resulted from changing Mesozoic stress episodes, involving NE-, E-, SE-, and S-directed extension. During significant NE-extension, F5 Six Mile synforms were stretched into separate grabens, which internally preserve F2 folds. NW diabase dikes (TE-9) formed by NE-extension. SE-extension was responsible for significant throw on regional NE faults.

Geological Society of America Abstracts with Programs. Vol. 48, No. 3

doi: 10.1130/abs/2016SE-271700

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