A NEW LOOK AT THE BAKERSVILLE INTRUSIVE SUITE: IMPLICATIONS FOR DELINEATING STRUCTURAL BOUNDARIES WITHIN THE BLUE RIDGE THRUST COMPLEX

The Bakersville Intrusive Suite consists of Neoproterozoic mafic dikes and gabbro bodies that intrude Grenville basement in the Blue Ridge thrust complex of western North Carolina and eastern Tennessee. These dikes predate Paleozoic orogenic events, and therefore are indicators of the grade of Paleozoic metamorphism in different thrust sheets. This study investigated the geochemistry and metamorphic assemblages of dike samples taken from I-26 between Mars Hill, North Carolina and Erwin, Tennessee. The dikes are contained within the Fries, Fork Ridge, and Linville Falls-Stone Mountain-Unaka Mountain thrust sheets, and represent a transition from high to low Paleozoic metamorphic grade. Field relations suggest that mafic dikes in our study area are part of the Bakersville Suite but little published geochemical data are available to support this interpretation. New geochemical data for 20 samples are internally consistent and are similar to Bakersville data of Goldberg et al. (1986), suggesting that dikes in our study area are part of the Bakersville Suite. Thus differences in metamorphic assemblages must reflect differences in Paleozoic metamorphic grade.

Previous work suggests that a thrust fault within the Fries thrust sheet, the Cox Creek fault, separates high grade dikes in the hanging wall from lower grade dikes in the footwall. In the upper part of the Fries, interpreted as the hanging wall of the Cox Creek fault, assemblages are characterized by abundant garnet, hornblende, and plagioclase with minor biotite. Structurally lower within the Fries thrust sheet (footwall of the Cox Creek fault) assemblages are dominated by abundant biotite, hornblende, and plagioclase; garnet is rare to absent. There is a notable difference in metamorphic assemblages between dikes contained within the Fries thrust sheet and the underlying thrust sheets. Dikes within both the Fork Ridge and Linville Falls-Stone Mountain-Unaka Mountain thrust sheets exhibit typical greenschist-facies metamorphic assemblages. Differences in metamorphic assemblages are evident across known thrust sheet boundaries and also within the Fries thrust sheet. Our data support the hypothesis that the Cox Creek fault separates higher grade dikes from lower grade dikes.