AN OVERVIEW OF NEW GEOLOGIC MAPPING OF THE CHAPEL HILL, HILLSBOROUGH AND EFLAND 7.5-MINUTE QUADRANGLES, CAROLINA TERRANE, NORTH CAROLINA

Theme Session: Recent Developments in Piedmont Geology

Recent USGS funded STATEMAP mapping in the Chapel Hill, Hillsborough and Efland 7.5-minute quadrangles in the North Carolina Piedmont has identified a regional scale anticlinorium parallel to the previously identified Virgilina Synclinorium. The study area is underlain by weakly metamorphosed Late Proterozoic volcano-sedimentary and intrusive rocks of the Virgilina sequence. The environment of deposition of the volcano-sedimentary sequence is interpreted to have been dominantly shallow marine with locally emergent (subaerial) volcanic centers approximately 630 million years ago. Intrusive rocks, which include the Chapel Hill pluton, complexly intrude the volcano-sedimentary sequence. During the Virgilina deformation (ca. 600 ma) the rocks were metamorphosed to the greenschist facies and folded into an anticlinorium with an axial plane dipping steeply toward the northwest. A mixture of dominantly primary pyroclastic rocks and lavas of the Hyco formation are exposed in the core of the anticlinorium with epiclastic lithologies of the Aaron formation dominating the flanks of the anticlinorium. The East Farrington pluton (ca. 579 ma) intrudes the folded and metamorphosed Virgilina sequence. Hydrothermally altered volcanic rocks with pyrophyllite deposits are concentrated along the informally named Cane Creek fault. The Cane Creek fault extends for at least 20 miles (30 kilometers) through the Hillsborough, Efland, White Cross and Saxapahaw 7.5-minute quadrangles. Brittle faults, attributed to Mesozoic continental rifting, separate sedimentary rocks of the Durham sub-basin from crystalline rocks of the Carolina terrane. Additional brittle faults are located within Carolina terrane lithologies.

Previously reported detrital zircon ages from the Aaron formation exposed in the Virgilina Synclinorium yielded a maximum age of ca. 578 Ma for the formation. Epiclastic rocks in the study area are correlated with the Aaron formation and are intruded by the recently U-Pb dated East Farrington pluton (ca. 579 Ma). This new data may indicate that the epiclastic rocks of the study area are not equivalent to the Aaron formation exposed in the Virgilina Synclinorium and may indicate that the stratigraphy of the Virgilina sequence needs to be re-evaluated.