Tectonic inversion and basement buttressing: an example from the central Appalachian Blue Ridge province

The structural geometry of the central Appalachian Blue Ridge province is primarily the result of Paleozoic contractional deformation. However, the Tye River fault zone in the western Blue Ridge of central Virginia preserves an extensional map pattern. These ENE–WSW striking faults place Neoproterozoic to early Cambrian volcanic and sedimentary rocks over Grenvillian granitic basement. Detailed mapping, cross-section restoration, and balancing reveals partially inverted faults, original half grabens, and significantly thicker cover units on hanging walls. The orientation and geometry of the Tye River fault zone, as well as the thickness changes in the cover rocks are inconsistent with extensional reactivation of Paleozoic reverse faults during Mesozoic rifting. The extrusion and deposition of cover rocks was contemporaneous with normal displacement on the Tye River fault zone and the formation of rift basins recording ∼5% crustal extension. Faults were reactivated as Paleozoic contractional structures, but an extensional map pattern is generally still preserved. Regional shortening of 10–20% was accomplished primarily by folding of the cover rocks rather than by reactivation of older faults. The basement formed a rigid buttress that controlled the geometry of folding in the cover sequence.