THE REDEFINED VIRGILINA SEQUENCE: A NEW LITHOTECTONIC UNIT IN CAROLINIA, SOUTHERN APPALACHIANS OF NORTH CAROLINA AND VIRGINIA

The Virgilina sequence is a lithotectonic unit within Carolinia, a major peri-Gondwanan crustal block in the southern Appalachians. The sequence has traditionally been thought to be conformable and include the Neoproterozoic Hyco and Aaron formations, and interlayered Virgilina volcanics; however, recent geochronology has revealed a major time gap between the Hyco and Aaron formations. Consequently we redefine the Virgilina sequence to include only the Aaron formation and Virgilina volcanics.

The redefined Virgilina sequence is composed of low-grade metamorphic felsic - mafic volcanics and associated clastic sedimentary rocks. It is disposed in a large-scale syncline overturned to the NW with an axial trace trending NNE. Observations taken from detailed geologic mapping at the 1:24,000 scale indicate a disconformity between the Hyco formation and the Virgilina sequence with no deformational event prior to deposition of the sequence. In conjunction with field observations, high precision magnetometry was used to more accurately locate contacts between rock units. To better constrain the magnitude of the lacuna, U-Pb zircon age dating has been attempted on a sample from the upper Hyco formation. Combined with existing geochronology, the data suggest the lacuna to be on the order of 37 m.y.

The traditional conformable Virgilina sequence has been used by previous workers in correlating Carolinia with the northern Appalachian Avalonia, the two largest exotic blocks in the Appalachian orogen. However, on the basis of other geologic characteristics, their developmental paths have been shown to be distinct. This study contributes new data to help further evaluate this comparison.