PETROGENESIS OF AMPHIBOLITE BLOCKS FROM THE TATHAM'S CREEK/SAVANNAH CHURCH AREA, NORTH CAROLINA BLUE RIDGE

Rocks of the Cullowhee Terrane of western North Carolina preserve ubiquitous block-in-matrix lithologies which may provide a glimpse into accretionary processes during the earliest stages of mountain building in the southern Appalachians. A variety of variably deformed amphibolite blocks ranging in their long dimensions from a few cm to several meters are enclosed within meta-sedimentary migmatitic biotite schists and gneisses exposed in road-cuts at Tatham's Creek/Savannah Church (see Raymond et al 1989), and points east along US 23/76 toward Dillsboro, NC. Microscope petrography and chemical documentation of major and minor mineral phases in the amphibolites, were used to document mineral assemblages and infer the metamorphic petrogenesis of these units.

Thin sections of the amphibolites were prepared, examined via petrographic microscope, and geochemically analyzed utilizing the remotely operable JEOL 8900R Superprobe electron microprobe facility at the Florida Center for Analytical Electron Microscopy (FIU). The felsic matrix of the rocks at Tathams consist of quartz + biotite + plagioclase + garnet, and grade in fabric from schist to gneiss. The amphibolite blocks are composed of hornblende ± garnet ± biotite ± ilmenite, with uncommon plagioclase, with minor titanite rimming ilmenites. The garnet + amphibole assemblage in the blocks and the lack of observable rutile or sillimanite in the rocks place their peak metamorphic conditions in the upper amphibolite facies, with retrogression to middle amphibolite facies indicted by the development of biotite at the expense of amphibole + garnet, and titanite after ilmentie. Various geothermometry and geobarometry models were utilized to determine the moderate pressure and high temperature of this metamorphic assemblage. Temperatures in the range of 654° ± 10°C were determined for the system and were used in correlation with the average pressure of 8 kbar. (see Powell & Powell 1977 and Schmidt 1992). The blocks represent basalt protoliths within an argillaceous sedimentary matrix that was subsequently metamorphosed within a collisional system.