MAGNETIC CONSTRAINTS ON THE NATURE OF THE BREVARD ZONE ADJACENT TO THE GRANDFATHER MOUNTAIN WINDOW, COLLETSVILLE, NC

The NE/SW trending Brevard Fault zone (BFZ) is a series of linear faults that strike subparallel to the southern Appalachian Mountains and delineates the Blue Ridge from the Tugaloo Terrane (western Inner Piedmont). There have been many investigations of this fault zone, but questions remain regarding its geometry and nature. However, throughout its extent, the fault is generally characterized as a high temperature ductile shear zone. While it may or may not be a terrane bounding feature, southeast of the Grandfather Mountain window it separates Proterozoic Laurentian crust and the Ordovician Tugaloo Terrane. We present preliminary results of a study examining the nature of the BFZ in the Colletsville quadrangle, NC.

Understanding the geometry, deformation, and strain history of the BFZ can help answer questions regarding the lithotectonic evolution of the southern Appalachians, the nature of the boundary between Laurentian margin and accreted terranes, and the nature of major tectonic boundaries in other orogenic systems.

Preliminary field measurements indicate that regardless of rock type (e.g., amphibolite, biotite or muscovite schist, gneiss, or granitoids) foliation consistently strikes NE and dips SE. However, lineation varies across the BFZ. South of and within the BFZ mineral stretching lineations are subparallel to foliation and have an average plunge of ~ 9º while mineral lineations to the north of the zone are down dip and have an average plunge of ~52º. Such a structural change is consistent with the BFZ as a rheological boundary between Laurentian margin rocks and accreted terranes.

Furthermore, regional aeromagnetic data show the BFZ as a lineament indicating that the rocks can be magnetically mapped and modeled to constrain the 3-d geometry of the boundary. Preliminary geologic mapping demonstrates that the rock unit magnetic susceptibility ranges from -0.038 to 27.50 * 10^-3 SI. Additionally, we use anisotropy of magnetic susceptibility (AMS) to quantify mineral stretching lineations, intensity, and define the fabric where it is cryptic.

The whole of these data sets will help to build a map and structural model, and answer questions regarding the nature and relationship of the Brevard Fault zone and Tugaloo Terrane.