Spatz, A. (2019). STRUCTURAL ANALYSIS OF METASEDIMENTARY AND METAVOLCANIC UNITS IN UWHARRIE NATIONAL FOREST: DETERMINATION OF A POSSIBLE FOLD STRUCTURE. Unc Charlotte Electronic Theses And Dissertations.
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 mid-Paleozoic orogeny is represented by greenschist facies metamorphism and generally northwest-dipping slaty cleavage that is approximately axial planar to regional folds. These folds verge toward the southeast. We have investigated very detailed cleavage-bedding relationships in the Tillery and Cid formations of the Albemarle Group in Uwharrie National Forest, North Carolina. These relationships were used to determine a characteristic fold geometry that explains local, sometimes sharp variations in bedding attitudes, and to apply these results to a postulated but previously undetected doubly-plunging antiform outlined by two horseshoe-shaped metavolcanic units previously mapped as either one unit in the upper part of the Tillery Formation or as two different units in the upper Tillery and lower Cid formations. We propose that this outcrop pattern is the effect of the closures 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 lower contact(s) between metavolcanic and metasedimentary rocks often show that this contact follows topographic contours, suggesting low dip angles. We have remapped this contact and found that in many locations the contact can be placed farther upslope in ephemeral stream valleys, thus changing map projections to better represent dips controlled by folding. Where the contact coincides with fold hinges, however, it is possible for the contact to be locally horizontal. Our conclusion is that the map geometry may reflect folding of a single volcanic unit (though more geochemical analysis is needed), that together with stratigraphically lower argillite composes the main doubly plunging, northeast-southwest anticline.