THE CENTRAL AND SOUTHERN APPALACHIAN BLUE RIDGE PROVINCE: ALONG-STRIKE VARIATION AT THE APPALACHIAN OROGEN’S THICK- TO THIN-SKINNED DEFORMATION FRONT

The Blue Ridge province forms a major structural element in the central and southern Appalachian Orogen. The Blue Ridge province extends more than 1,000 km from southern Pennsylvania to Alabama, tracing a wide swath across multiple salients and recesses. The Blue Ridge is distinctive because it: 1) exposes Mesoproterozoic basement, 2) includes the Ediacaran/Cambrian rifted margin that formed along Laurentia’s southeastern edge, and 3) bounds the thin-skinned Appalachian foreland fold-and-thrust belt. However, the structural style of the Blue Ridge changes significantly from the central to the southern Appalachians.

Northward from central Virginia, the province is a broad basement-cored anticlinorium which formed during NW-directed contractional deformation and greenschist facies metamorphism that occurred ~370 and 330 Ma (Acadian to Neoacadian). Later, as the Appalachian foreland fold-and-thrust belt developed between ~300 and 280 Ma (Alleghanian), the northern Blue Ridge was a relatively cool and strong massif that was thrust, out-of-sequence onto Paleozoic strata in the foreland.

The southern Blue Ridge, to the south of Roanoke Virginia, records a more complex Paleozoic history that includes structural elements from an Ordovician accretionary wedge complex, multiple magmatic pulses, high grade metamorphic events, and significant transpressional faulting. Exposed Mesoproterozoic inliers include high-grade gneiss domes as well as faulted-bounded windows through duplexed in-sequence Alleghanian thrust sheets. The contrasting style of deformation across the Appalachian Blue Ridge province reflects both a tectonic inheritance from the pre-Appalachian rift structures and associated strata as well as differences in the Paleozoic thermal history along the Laurentian margin during subduction and collisional tectonism.