STRUCTURAL EVOLUTION OF THE SAURATOWN MOUNTAIN QUARTZITES; EVIDENCE FOR POLYPHASE DEFORMATION AND SHEARING

Quartzites exposed in the Sauratown Mountains, NC provide a unique record of several phases of deformation along the continental margin during the Paleozoic. Sauratown quartzites represent a continental margin sedimentary package that was deposited on top of Mesoproterozoic (1.2Ga) schist and gneisses. The Sauratown Mountains window exposes the core of a broad anticlinorium containing intensely deformed interlayered quartzite (1-3m) and pelite (1cm – 10cm). Previous work suggests that following their deposition along the continental margin these rocks were transported westward from their original locations as part of the Blue Ridge – Piedmont thrust sheet to their current location in the western piedmont.

Relationships between overprinting, crenulation cleavage, and stretching lineations record three phases of deformation (D1-D3). Isoclinal recumbent folds (F1) trend east-west and are the earliest generation of folding. The axial surfaces (S1) create a pervasive sub-horizontal foliation throughout the outcrop. Isoclinal F1 folds are overprinted during D2 by southeast vergent, shallowly to moderately plunging (0º-32º) open F2 folds (N40ºE-N65ºE). Open folds are most commonly preserved in the pelitic layers and define a dominant crenulation in pelitic rocks associated with a steeply dipping southeast vergent foliation (S2). Stretching lineations are prevalent throughout the outcrop and are sub-parallel to the orogen. Previous work suggests that these stretching lineations were generated during D1 and D2 (L1 and L2) and then rotated to their current orogen parallel orientations by later warping (F3, F4) of the anticlinorium. However, it is possible that L1 and L2 stretching lineations were rotated to their current orientations by oblique convergence or shearing. Stretching lineations common in highly strained quartz veins are sub-parallel to the prominent stretching lineation throughout the outcrop indicating that crystal plastic processes accommodated some deformation during D3. These lineations (L3) record NE-SW extension when L1 and L2 were rotated into parallelism with L3. Together this evidence suggests that two phases of deformation in the Sauratown quartzites culminated in final phase of orogen-parallel extension.