PETROGRAPHIC AND FIELD RELATIONS OF A PORTION OF THE CARROLL KNOB MAFIC/ULTRAMAFIC COMPLEX, EASTERN BLUE RIDGE, MACON CO., NC

Field and petrographic investigations as part of a NSF-REU summer research project in the Carroll Knob complex, western North Carolina, focused on two small areas, the type Carroll Knob (CK) area and the Jones Creek (JC) area. Four mappable mafic/ultramafic lithologies were identified: metadunite (including anthophyllite-talc schists), metapyroxenite, metagabbro, and amphibolite. In addition, metatroctolites and pale green amphibolites are present locally. Evidence for dominant mid- to upper- amphibolite facies metamorphic conditions includes amphibole + Ca-plagioclase ± garnet ± epidote in mafic rocks, and staurolite + garnet assemblages in metasedimentary rocks.

Around Carroll Knob, metadunite, metapyroxenite, and metagabbro form elongate, NE-trending, foliation-parallel lenses within the dominant amphibolite, and are concentrated near the southern contact with the Tallulah Falls Formation. A calc-silicate unit follows this southern contact. Contacts among the ultramafic units appear to be gradational, and lithologies are often interlayered on the meter scale. Post-emplacement folding formed tight, NE-trending, steeply inclined folds.

At Jones Creek, the dominant mafic rocks include dark to pale-green amphibolite, and metagabbro. Two lenses of ultramafic rocks, including metadunite, talc-amphibole schist, metapyroxenite, and metatroctolite, are generally oriented parallel to the regional foliation.

The mafic-ultramafic lithologies and gradational contacts between CK units are similar to the nearby Buck Creek complex; however, the relative proportions differ. Gabbroic rocks are volumetrically more significant at Carroll Knob, while metadunites and metatroctolites are more significant at Buck Creek. Preservation of relict cumulate textures in some Carroll Knob mafic exposures suggests a magma-chamber origin.