Metamorphism of carbonaceous material in the Tono contact aureole, Kitakami Mountains, Japan

Abstract

Optical and X-ray studies of carbonaceous material in the Tono contact metamorphic aureole, Kitakami Mountains, northeast Japan, have revealed that metamorphic graphitization proceeded through two discontinuous changes: first, optically anisotropic domains develop within the coaly phytoclast, forming transitional material, and then, ordered graphite crystallizes by the decornposition of pre-existing carbonaceous materials. Coaly material disappears in the uppermost chlorite zone. Transitional material appears in the middle of the lower chlorite zone. Graphite appears in the upper chlorite zone and its modal abundance increases across the andalusite isograd to the cordierite isograd where all the carbonaceous materials have converted to graphite. The apparently continuous variation in the crystallographic parameters of the bulk carbonaceous material during graphitization is largely due to variation in the modal proportions of three types of carbonaceous materials. The temperature of graphitization in the present area is at least 100°C higher than the temperature in the Sanbagawa and New Caledonia high-pressure metamorphic terrains, probably due to the slow reaction rate of metamorphic graphitization and to the short duration of contact metamorphism.

Coal-Bearing Depositional Systems

“…The samples which in Fig. 3.33 display signs of early graphitisation in comparison to their still moderate coal rank come from high pressure metamorphic terrains, for which the observations on naturally occurring high rank coal and graphite by Bostick (1974), Ragot (1976, Diessel et al (1978), Bonijoly et al (1982), Okuyama-Kusunose and Itaya (1987) and the experimental work of Noda and Kato (1965);Noda (1968);and Inagaki et al (1977) suggest that high pressure retards coalification but accelerates graphitisation even of relatively "nongraphitisable" carbon.…”

Conversion of carbonaceous material to graphite within the Greywacke Zone of the Eastern Alps

“…Organic matter is a common component of metasedimentary rocks and is transformed progressively under rising temperature and pressure conditions. This process can be traced quantitatively by organic petrology (e.g., Diessel and Offler 1975;Diessel et al 1978;Okuyama-Kusunose and Itaya 1987;Rantitsch 1995;Suchy et al 1997), X-ray diffraction (e.g., Landis 1971;Grew 1974;Diessel et al 1978) and Raman spectroscopy (Pasteris and Wopenka 1991;Jehlicˇka and Be´ny 1992;Wopenka and Pasteris 1993;Yui et al 1996;Beyssac et al 2002aBeyssac et al , 2002b. High resolution transmission electron microscopy (HRTEM) allows a qualitative description of the mechanism of transformation (e.g., Bonijoly et al 1982;Buseck and Huang 1985;Oberlin 1989;Zheng et al 1996;Beyssac et al 2002a;Ferreiro Ma¨hlmann et al 2002).…”

Microstructural evolution of carbonaceous material during graphitization in the Gyoja-yama contact aureole: HRTEM, XRD and Raman spectroscopic study

“…4), these parameters are also important indicators to the degree of graphitization. Nakamura Kusunose and Itaya, 1987;Tsuchiya et al, 1987;Naka mura, 1995) and regional metamorphism (Itaya, 1981;Wang, 1989) modified after Tsuchiya (1994). Black dotted lines indicate the region where CM is converted to the fully ordered graphite (d 002 ≤3.36 Å) in the respective studies.…”

“…However, it seems that the temperature at which fully ordered graphite (d -spacing ≤3.36 Å) form, is different for regional and contact metamorphism as shown in many earlier studies (Grew, 1974;Itaya, 1981;Okuyama -Kusunose and Itaya, 1987;Wada et al, 1994;Nakamura, 1995). Tsuchiya (1994) and Okuyama - Kusunose and Itaya (1987) compiled the peak metamorphic temperatures and the degree of graphitization from different localities. They proposed that the difference of duration of heating affect the difference of d 002 spacing, which is observed in contact and regional metamorphisms.…”