Thermal Effect of Granite Pluton on Graphitization of Carbonaceous Material in the Kuga Group, Southwest Japan

Abstract

The Kuga Group of Triassic-Jurassic age is mainly composed of black pelitic rocks and chert which were thermally metamorphosed by intrusion of Cretaceous granite. Graphitization of carbonaceous material in pelitic rocks of the Kuga Group was investigated using X-ray diffraction method. Samples were collected from six boreholes, of which three boreholes reached to the granite.
Crystallite thickness L_c(002) value increases toward the granite pluton and is 300Å at a vertical distance of 200-300m from the contact. Near the contact L_c(002) is 400Å or more. Lattice strain ε_c decreases with increasing L_c(002).
Vertical and lateral changes in L_c(002) of carbonaceous material in the Kuga Group are illustrated in the geological section showing the isopleth of L_c(002). The isopleth of L_c(002) is generally parallel to the contact. These features suggest that heat transfer through the Kuga Group depends chiefly on thermal conduction. Graphitization of carbonaceous material in sedimentary rocks is applicable to the prediction of the subterranean pluton.