Paper No. 10-9
Presentation Time: 8:00 AM-12:00 PM
CLEAVAGE BEDDING RELATIONSHIPS IN TILLERY FORMATION ARGILLITE, CAROLINA TERRANE, NORTH CAROLINA
Cambrian metasedimentary and metavolcanic rocks in the Albemarle Group in southcentral 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 are vergent to the southeast. We have investigated very detailed cleavage-bedding relationships in the Tillery and Cid formations of the Albemarle Group in Uwharrie National Forest. 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. While individual outcrops are abundant, it is rare to find mesoscopic fold closures in the area. Our spatial statistics suggest that the geometrical exemplar for primary folds is steeply inclined to overturned, verges southeast, and plunges moderately northeast. Rare viewable closures confirm this geometry. Pervasive cleavage, while anastomosing, is axial planar to these folds. Previous mapping of the lower contact(s) between metavolcanic and metasedimentary rocks often show this contact following topographic contours, suggesting low dip angles. We have remapped this contact and found that in many locations the contact can be pushed farther upslope in ephemeral stream valleys and thus changing map projections to better represent dips controlled by folding. Also, steep slopes along the contact are frequently covered by metavolcanic scree and debris flows. Where the contact coincides with fold hinges, however, it is possible for the contact to be locally horizontal. Our preliminary conclusion is that the map geometry reflects folding of a single volcanic unit rather than two stratigraphically separate units.