LONG-TERM MID-CRUSTAL RESIDENCE TIME OF THE NORTH CAROLINA EASTERN BLUE RIDGE

A NE-SW-trending arcuate belt of low-K trondhjemitic to granodioritic plutons is exposed in the southern Appalachian eastern Blue Ridge (EBR) province of Georgia and North Carolina. Previous studies of some EBR plutons focused on their elemental and isotopic chemistry and have shown that they are typically Ordovician (~465 Ma), Devonian (~375 Ma), or Mississippian (~335 Ma) in age. Most EBR plutons yield crystallization ages near those cited above, however, no spatial relationship exists between pluton age and / or composition. Detailed field studies of EBR plutons are rare, and little is known about how they fit into the broader Paleozoic orogenic framework.

Despite the lack of detailed field-based studies, EBR plutons are critically important for deciphering details and timing of multiple overprinting Paleozoic deformation events. Here focus is given to some of both the oldest and youngest Paleozoic plutons exposed in the EBR of western North Carolina. Field relationships combined with new thermobarometric analyses on granitoids and host rock indicate that magmatism was associated with waning stages of Taconian and Alleghanian deformation, and that little exhumation occurred during the intervening 130 million years separating these major tectonic events. These new data imply this portion of the EBR remained at mid-crustal levels (i.e., 9-7 kbar or 25-20 km depth) from the mid-Ordovician until at least the early Mississippian.