Carbonaceous material in the Ryoke metamorphic rocks, Kinki district, Japan

Carbonaceous material in the Ryoke pelitic metamorphic rocks in the Wazuka area, Kinki district, Japan, has been studied by X-ray diffraction (XRD) analysis. Detrital graphite in the lower-grade rocks is recognized in both X-ray diffractograms and transmission electron micrographs. Progressive graphitization is considered to have proceeded continuously on the basis of the XRD data of the bulk concentrates of carbonaceous material, and a conspicuous asymmetric shape of XRD peaks in lower-grade samples is ascribed to the mixture of carbonaceous materials with different crystallinities. Fully-ordered graphite does not occur until the highest-grade part of the chlorite-biotite zone. The variation of degree of crystallinity of carbonaceous materials inferred from XRD data is consistent with the prograde mineral zones. The temperatures for the development of fully-ordered graphite are estimated to be between 410° and 440°C in regional metamorphism through comparing the XRD data from low-, medium- and high-pressure types of metamorphic terrains.