3D RESTORATION OF THE NEOPROTEROZOIC SUGAR HOLLOW RIFT BASIN USING STRAIN AND VORTICITY ANALYSIS, BLUE RIDGE, CENTRAL VIRGINIA

The central Appalachian Blue Ridge province is largely the result of Paleozoic contractional deformation, but Neoproterozoic rift structures are preserved at Sugar Hollow in central Virginia. On the western limb of the Blue Ridge anticlinorium, the Neoproterozoic rift sequence includes the siliciclastic Swift Run and basaltic Catoctin formations that unconformably overlie Mesoproterozoic granitoid basement. Typically, the Swift Run Formation is a thin (<20 m thick) unit, but at Sugar Hollow the Swift Run Formation crops out over an area of 12 km2 and reaches a thickness of >300 m. New geologic mapping of Sugar Hollow identified 7 NE-striking normal faults that place the Neoproterozoic cover sequence on basement and frame an eastward-thickening graben complex. The Sugar Hollow basin is bound to the east by the White Hall high-strain zone which experienced W to NW directed reverse displacement of ~1 km. Paleozoic contractional deformation reactivated and imbricated the normal faults producing open to overturned folds in the hanging wall. The White Hall high-strain zone may have originated as the master fault to the Sugar Hollow basin and was later sheared into a easterly dipping high-strain zone. Deformation occurred under greenschist facies conditions and the rocks are penetratively deformed. Si and K were highly mobile elements and syntectonic quartz and K-feldspar veins are common. An array of 6 cross sections were constructed orthogonal to the faults using Midland Valley's Move software to create a 3D model of Sugar Hollow. Initial fault and fold restoration modeling indicates that Sugar Hollow experienced a total shortening of 30% to the NE but only 5% in the SW. Further modeling in Move will reconstruct the geometry of the basin during the Neoproterozoic to determine the original depositional thickness of the Swift Run Formation. Additionally, modeling with Move allows accounting of strain and volume change accrued during restoration. These data can then be compared to strain and vorticity measurements made at the hand sample and thin-section scale in order to evaluate their usefulness as an analytical tool.