Crustal structures and the eastern extent of lower Paleozoic shelf strata within the central Appalachians: A seismic reflection interpretation

Reprocessing of line PR3 proprietary seismic reflection data has delineated Grenvillian, Paleozoic, and Mesozoic structures within the Appalachian foreland, Blue Ridge, and Piedmont of the central Appalachians in Virginia and West Virginia. The eastern portion of PR3 can be correlated along strike with the western portion of line I-64, reprocessed earlier at Virginia Tech. The combined seismic reflection data image the crust from the eastern Valley and Ridge, Blue Ridge, Piedmont, and Atlantic Coastal Plain provinces. Within the Piedmont, large (as much as 10 km wide) reflective structures imaged on both lines PR3 and I-64 are interpreted to be thrust sheets that might be composed of deformed Catoctin, Evington Group, and possibly younger metamorphosed rocks. A concealed extension of the Green Springs mafic mass intrudes a thrust sheet imaged along the PR3 profile. The Blue Ridge-Piedmont allochthon was transported north-west along the Blue Ridge thrust, which ramps upward ∼12 km east of the surface exposure of the Mountain Run Fault. Westward along line PR3, the Blue Ridge thrust maintains an undulating geometry; the maximum thickness of the Blue Ridge allochthon is interpreted to be ∼4.5 km. The Blue Ridge allochthon is generally acoustically transparent and overlies lower Paleozoic shelf strata. The maximum thickness of these strata is ∼8 km. Shelf strata are interpreted to extend in the subsurface 5 km east of the surface exposure of the Mountain Run Fault, the northeastward extension of the Brevard Fault Zone, where they are truncated by the Blue Ridge thrust at a depth of 10.5 km (3.5 s). Various folds and blind thrusts are imaged beneath the Appalachian foreland; however, the foreland has not experienced the same degree of deformation as observed in the eastern provinces. A basement uplift ∼45 km wide is imaged beneath the Valley and Ridge province and is interpreted as having formed prior to Late Cambrian time. Farther west, reflections imaged beneath the Glady Fork anticline in the Appalachian Plateau are interpreted as a positive flower structure associated with wrench fault tectonics. Relatively few deep (>9 km) crustal reflections are imaged along line PR3. The majority of reflections that do exist at these depths are observed beneath the Piedmont and eastern Blue Ridge. The high reflectivity associated with the Grenvillian basement in these areas might be the result of the Paleozoic orogenies and extension related to Late Proterozoic and Mesozoic rifting.