@article{oai:nagoya.repo.nii.ac.jp:02001125, author = {TSUKADA, Kazuhiro and SHIMURA, Yusuke and NADMID, Bayart}, journal = {名古屋大学博物館報告, Bulletin of the Nagoya University Museum}, month = {Mar}, note = {A major problem for understanding the tectonic history of the Inner zone of Southwest Japan is the spatial tectonic contrast between the rocks in its western and eastern parts. In the western part of the zone, the Sangun–Renge, Akiyoshi, Maizuru, and Ultra-Tanba belts are widely exposed, whereas they are fragmented in a narrow area along the Hida Gaien belt in the eastern part. The Hida Gaien belt with its fault-bound blocks is thus a key unit for understanding the geology. The lithostratigraphy and structure of the blocks composed of volcanic/sedimentary rocks have been studied previously (e.g., Tsukada et al., 2004), but few attempts have been made to study the blocks of ultra-mafic rock which are critical to understanding the tectonic process in the Hida Gaien belt. In the Nakao area, Takayama City, Ordovician(?) mafic volcanic rocks (the Iwatsubodani Formation) of the Hida Gaien belt have been thrust onto an unclassified block of Kurotani ultramafic rock (KUM). This paper describes the mineral chemical composition of rocks from the KUM and the Iwatsubodani Formation and discusses the magmatic relationship between their clinopyroxene (Cpx) chemical composition. The Mg# (= Mg/(Mg + Fe) mol%) of Cpx in the KUM is 0.93–0.98. In the Iwatsubodani Formation, sub-ophitic lava (Mg# of interstitial Cpx = 0.41–0.79) is overlain by pyroclastic rock with abundant clasts of porphyritic lava (Mg# of Cpx porphyry = 0.75–0.90). In the variation diagram, most elements of Cpx from the KUM and Iwatsubodani Formation form a linear trend against Mg#. Thus, the KUM and Iwatsubodani Formation probably both originated through fractionation from a single magma source. Although the porphyritic lava overlies sub-ophitic lava in the Formation, the Mg# of Cpx in the porphyritic lava is much higher than that of the underlying sub-ophitic lava. This fact suggests that the Cpx porphyry of the porphyritic lava had probably crystalized in a magma chamber before the sub-ophitic lava stage.}, pages = {53--68}, title = {The magmatic relationship between the "Kurotani ultra-mafic rock" and the Ordovician(?) Iwatsubodani Formation, Takayama City, Hida Gaien belt, central Japan : the chemical composition of clinopyroxene}, volume = {36}, year = {2021} }