The Nature and Timing of Deformation in the Beech Mountain Thrust Sheet between the Grandfather Mountain and Mountain City Windows in the Blue Ridge of Northwestern North Carolina

Abstract

Detailed field, petrographic, and isotopic studies provide new constraints on the nature and timing of deformation in part of the Blue Ridge thrust complex in northwestern North Carolina. The Linville Falls, Stone Mountain, and Long Ridge faults, and other smaller-scale shear zones in the Beech Mountain thrust sheet show evidence of episodes of alternating ductile and brittle deformation. The resulting fault rocks include ultramylonite, ultracataclasite, and pseudotachylyte(?). Fluid phases were involved in the formation of the major shear zones and were responsible for Rb-Sr isotopic re-equilibration in strongly deformed tectonites. Our multidisciplinary study supports earlier suggestions that the latest major movement of the Blue Ridge thrust complex in the southern Appalachians occurred under mid- to upper-greenschist facies conditions during the Alleghanian orogeny around 300 Ma.