MINERALOGY, PETROCHEMISTRY, AND METAMORPHIC CHANGES IN METAULTRAMAFIC ROCKS ACROSS THE ASHE METAMORPHIC SUITE OF NORTHWESTERN NORTH CAROLINA

Bodies of metaultramafic rocks are a widely distributed component of the Ashe Metamorphic Suite in the eastern Blue Ridge Belt of northwestern North Carolina. From the Grandfather Mountain Window northeast to southern Virginia, both quartz-deficient, locally Talc-, Chlorite-, and/or Mg-amphibole-bearing schists and diablastites (TC-amphibolites) and olivine- and orthopyroxene-dominated metaultramafic rocks show regional changes in mineral character and metamorphic grade. Mineralogy reveals that at least some metaultramafic TC-amphibolite bodies are petrologically heterolithic. Higher grade olivine- and orthopyroxene-dominated rocks of upper amphibolite grade show progressive changes to Mg-hornblende and Mg-actinolite dominated and locally serpentine-bearing, lower amphibolite to greenschist facies assemblages from SW to NE across the region. Three to five metamorphic assemblages within the rocks reflect incomplete recrystallization in response to multiple metamorphic events. Rocks to the northeast experienced greater deformation and more pervasive lower grade recrystallization than rocks to the southwest. The changes, in part, mimic changes in associated Quartz- and Feldspar-bearing, hornblende-rich QF-amphibolites of oceanic mafic parentage. While a few of the TC-amphibolites had mafic protoliths, the petrochemistry reflected by MgO-CaO-Al₂O₃ chemistries and trace element ratios reveals that the majority of the metaultramafic rocks had ultramafic plagioclase peridotite, peridotite, pyroxenite, and dunite protoliths. Contacts of metaultramafic bodies are pre-late metamorphic, but some are syn- and post-metamorphic ductile and brittle faults formed during and after the last major metamorphism. These rocks likely represent ophiolite fragments of varying character deformed and dismembered during assembly of the orogenic belt.