CHARACTERIZATION OF 3-D VORTICITY AND STRAIN SYMMETRY IN THE SOUTHERN APPALACHIAN INNER PIEDMONT: AN EXHUMED OROGENIC HINTERLAND

Recently, a number of studies have proposed 2-D tectonic models for crustal flow in ductilely deforming orogenic hinterlands and some researchers have even proposed more realistic models involving complex 3-D flow. While these preliminary models are certainly founded on rigorously synthesized field and analytical data, few attempts have been made to quantitatively characterize ductile flow components, particularly 3-D vorticity and strain symmetry. In order to test these rapidly emerging ideas, new investigations focused on constraining the quantitative characteristics of ductile flow are necessary.

The Inner Piedmont (IP) of North Carolina, South Carolina, and Alabama extends ~700 km along strike and represents the high-grade Neoacadian (Late Devonian-Mississippian) orogenic core of the southern Appalachians. The IP is bounded to the northwest by the Brevard fault zone and to the southeast by the Central Piedmont suture. Hatcher and Merschat (2006) suggested the existence of a Late Devonian orogenic channel with NW- to west- to SW-directed flow of ductile material. Although detailed vorticity estimates were not obtained by that study, crustal scale vorticity estimates placed IP flow in the realm of simple to sub-simple shear based on a number of fundamental assumptions. The ability to place quantitative constraints on ductile flow in a deeply exhumed orogenic system has major implications for our understanding of ductile hinterland evolution.

Vorticity and strain symmetry samples were collected along the Brevard-Bowens Creek fault zone from Lake Jocassee, SC to south of Roanoke, VA. Quantitative characterization of flow in the IP represents a meaningful and unique addition to the broader scope of our research because (a) methods comparable to ours have not been applied to a deeply exhumed orogenic hinterland and, (b) the relatively complex flow paths proposed by previous researchers in the IP have never been rigorously investigated in terms of strain symmetry and vorticity.