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Wednesday, April 26 • 12:30pm - 2:00pm
Kinematic And Deformation Temperature Constraints During Acadian Dextral Strike-Slip Faulting On The Burnsville Fault In Asheville, NC

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The Appalachian Orogen records three mountain building events attributed to the creation of Pangaea; the Ordovician Taconic, Silurian-Devonian Acadian, and the late Paleozoic Alleghanian orogenies. In North Carolina, the rocks of the Ashe Metamorphic Suite were juxtaposed onto ~1 billion year old basement rocks during the Taconic. This contact was reactivated during the Acadian by the dextral strike-slip Burnsville shear zone, recognized by previous studies from Asheville north to Carvers Gap, NC. This study presents detailed field mapping and kinematic analysis of rocks collected along a transect through the Burnsville shear zone in Asheville, NC. Field observations and microstructural analysis of the rocks were combined with electron-backscattered diffraction (EBSD) analysis to quantify the amount and the depth of dextral shearing that occurred during the Acadian orogeny. Shear sense indicators seen in the field and microscopically supports dextral strike-slip shearing. EBSD and microstructural measurements were combined to calculate the vorticity (Wm; the ratio of flattening to shearing where 1 suggests shearing and 0 suggests flattening) and the strain ratio (Rxz; the ratio of the axes of flattening and shearing). Results indicate a Wm of 0.99 (minor flattening) and Rxz of 5.4, suggesting the rocks in one portion of the shear zone were shortened by 12.5% perpendicular to foliation and extended by 14.3% parallel to shear zone foliation. These data were collected from a sample with a lower strain, suggesting that the bulk extension and shearing across the shear zone is higher. Estimates of deformation temperatures from quartz lattice preferred orientations (LPO) collected from EBSD analysis as well as evaluation of quartz recrystallization suggest a temperature of ~600° C during Acadian dextral shearing, a depth of ~20 km. U-Pb ages from zircon in an undeformed granite dike that crosscuts the shear zone indicates that dextral shearing ended by ~330 Ma.


Wednesday April 26, 2017 12:30pm - 2:00pm PDT
Concourse - Wilma Sherrill Center