STRUCTURAL ANALYSIS OF METASEDIMENTARY AND METAVOLCANIC UNITS IN UWHARRIE NATIONAL FOREST: DETERMINATION OF A POSSIBLE FOLD STRUCTURE

Cambrian metasedimentary and metavolcanic rocks in the Albemarle Group in south-central North Carolina are part of the peri-Gondwanan Carolina terrane. These rocks are part of the Neoproterozoic to Cambrian Albemarle arc. The tectonothermal imprint left by a mid-Paleozoic orogeny is represented by greenschist facies metamorphism and northwest-dipping slaty cleavage, which is axial planar to southeast verging regional folds. We have investigated detailed cleavage-bedding relationships in argillitic and rhyolitic rocks of the Tillery and Cid formations of the Albemarle Group in Uwharrie National Forest, North Carolina. These relationships were used to determine the explanation for local, sometimes sharp variations in bedding attitudes, and to apply these results to a postulated but previously undetected doubly-plunging antiform. This antiform is outlined by two horseshoe shaped metavolcanic units previously mapped as either one unit in the upper volcanic sequence or as two separate units in the upper Tillery and lower Cid formations. We propose that this outcrop pattern is the effect of closures to the northeast and southwest of a doubly-plunging anticline. Our spatial statistics suggest that the geometrical exemplar for primary folds is steeply inclined to overturned, verges southeast, and plunges moderately northeast-southwest. Pervasive cleavage, while anastomosing, is axial planar to these folds. Previous mapping of the contact between the metasedimentary and metavolcanic rocks often show this contact following topographic contours, which suggests low dip angles. We have remapped this contact and found that in many locations the contact can be placed farther upslope in stream valleys, changing map projections to better represent dips controlled by folding. Where the contact coincides with fold hinges (including smaller parasitic folds), however, it is possible for the contact to be locally horizontal. Our conclusion is that the map geometry reflects folding of a single volcanic unit, that together with the stratigraphically lower argillite composes the main doubly plunging, northeast-southwest anticline.