Abstract

The Buck Creek ultramafic body, situated within a belt of alpine-type ultramafites in the North Carolina Blue Ridge, is completely enveloped by the Chunky Gal Mountain amphibolites. The mafic and ultramafic units were in contact prior to the earliest metamorphic and deformational events. The complex is at least partly bounded by a major thrust fault and appears to have been emplaced after the first stage of deformation. The amphibolites are divided into two units, types I and II, on the basis of texture, mineralogy, trace-element geochemistry, and geothermometry; however, these are indistinguishable in terms of major-element compositions. Type I amphibolites were metamorphosed under prograde granulite-facies conditions (∼725 ± 25 °C), whereas type II amphibolites were metamorphosed under prograde amphibolite-facies conditions (∼520 ± 20 °C); pressure was ∼4 to 6 kbar over the entire complex. A second, retrograde event was of middle green-schist facies. The amphibolites appear to have been derived from a cumulate gabbroic protolith, and probable igneous differentiation trends are preserved despite the high grades of metamorphism. This complex may represent either the basal section of an ophiolite sequence with calc-alkaline affinity, or a mafic pluton into which an ultramafic diapir intruded within a rifted continental environment.

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