Genesis of Graphite in Metapelites in the North-Western Border of the Lypniazhka Massif (the Inhul Domain of the Ukrainian Shield)

Abstract

This study presents results of an investigation of metamorphic rocks of the Inhul-Inhulets series located in the northwestern border of the Lypniazhka granite-migmatite massif (Inhul domain, the Ukrainian Shield). The rocks were studied petrographically and mineralogically and carbon isotope, Raman spectroscopic and microprobe measurements were made. Graphite and calcite were given special attention. Metapelites and quartz-rich graphite-biotite-garnet rocks were investigated. The former consist of biotite, graphite-biotite, amphibole-bearing graphite-biotite gneisses. Graphite in them is evenly distributed through the rock groundmass. The δС13 values of graphite lie between -39.4‰ and -33.6‰ (relative to PDB). The graphite is considered to be of biogenic origin. Quartz-rich graphite-biotite-garnet rocks are less common, but they also contain graphite. The latter occurs as inclusions in the major minerals either forming clusters. Its δС13 values fall between -28.45‰ and -22.2‰ (relative to PDB). Based on the Raman spectra, carbon from the gneisses has an ordered graphite structure. The temperature of graphite crystallization was estimated to be between 554 and 630°С and corresponds to the amphibolite facies.