Petrogenesis of the Chunky Gal Mountain mafic-ultramafic complex

The Buck Creek ultramafic body lies within a fairly continuous belt of alpine-type ultramafics in the North Carolina Blue Ridge. This body is completely enveloped by the Chunky Gal Mountain amphibolites. This paper explores possible relationships between these two lithologic units. Structural relationships indicate that at least three periods of deformation affected the entire complex. Cataclasis along portions of the mafic-ultramafic contact, and a thrust contact between the amphibolite and the surrounding Carolina Gneiss, indicate a tectonic mode of emplacement for all lithologies within the complex. The amphibolites are divided into two units. Type I and Type II, on the basis of texture, mineralogy, trace element chemistry, and geothermometry. Type I amphibolites were metamorphosed under prograde granulite facies conditions (~750°C) and oxygen fugacities approximate to the HM buffer, while Type II amphibolites were metamorphosed under prograde amphibolite facies conditions (~510°C) and oxygen fugacities approximate to the QFM buffer. Pressure was approximately 4-6 kb over the entire complex. A second, retrograde event was of lower greenschist facies. The amphibolites appear to have been derived from a cumulate gabbroic protolith, and many igneous differentiation trends are preserved despite the high grades of metamorphism. This complex may represent the basal section of an ophiolite sequence or a rifted continental mafic pluton into which an ultramafic diapir has intruded.