STRUCTURAL AND KINEMATC ANALYSIS OF THE EASTERN-WESTERN BLUE RIDGE CONTACT IN THE WEAVERVILLE QUADRANGLE, WESTERN NORTH CAROLINA

The contact between rocks of the eastern and western Blue Ridge is a fundamental tectonic feature of the southern Appalachian Mountains. In western North Carolina, the eastern Blue Ridge consists predominantly of metasedimentary and metavolcanic rocks of oceanic affinity (Ashe Metamorphic Suite), and apparently lacks Laurentian basement. The western Blue Ridge is characterized by Laurentian basement gneisses and intrusive rocks. The Ashe Metamorphic Suite (AMS) consists of pelitic schist, mica gneiss, amphibolite, calc-silicate rocks, pegmatite, and ultramafic rocks. In the Weaverville quadrangle, the AMS is separated from Laurentian basement rocks by a dextral strike-slip shear zone correlative with the Burnsville fault to the northeast. Adjacent basement rocks are predominantly biotite-hornblende gneisses, locally cut by Bakersville mafic intrusive rocks. The Burnsville fault is a mixed-rock mylonite zone that contains both AMS and basement rocks. Dunite and altered ultramafic rocks occur within this zone, and eclogite is locally present to the northeast near Bakersville, North Carolina. The shear zone has steeply dipping mylonitic foliation that strikes northeast. Mineral elongation lineations, interpreted as stretching lineations, trend northeast. Mesoscopic and microscopic kinematic indicators are consistent with dextral sense of shear. Outcrop-scale kinematic indicators include asymmetric porphyroclasts and pegmatite boudins. In thin section, mica fish, asymmetric porphyroclasts with tails, and broken and displaced plagioclase grains also give dextral shear sense. Mineral assemblages and deformation mechanisms indicate shearing occurred at amphibolite facies conditions. Reported ages of deformed pegmatites within the shear zone are ~ 380 Ma, indicating latest motion along the Burnsville fault was Devonian or younger in age. Preliminary mapping southwest of the Weaverville quadrangle indicates that the Burnsville fault continues into the Canton, North Carolina quadrangle. Thus, amphibolite-facies dextral strike-slip shearing can be documented for ~150 kilometers along the eastern-western Blue Ridge contact.