Atsushi MIYASHITA

The Kitomyo Schist from Kurosegawa Belt, Shikoku, has been long considered as the oldest records of subduction metamorphism in Japan, based on an early 1970s K-Ar dating of white mica. The schist consists of mafic and pelitic layers and occurs as a tectonic block within serpentinite. Reappraisal of the schist confirmed the schist is characterized by an epidote-amphibolite peak metamorphic facies. The mafic portion is characterized by zoned amphibole + epidote + chlorite + titanite phengite +/- rutile. The presences of relict rutile surrounded by titanite and the barroisitic cores of zoned amphibole suggest a high-pressure intermediate type metamorphism at the metamorphic peak (P = -0.8-1.5 GPa and T = -500-570 degrees C). The presence of Mn-rich garnet and the lack of biotite, oligoclase and paragonite also support high-pressure intermediate type metamorphism that eliminate the possibility of a typical blueschist-facies metamorphism. New SHRIMP and LA-ICPMS zircon U-Pb geochronology on a pelitic sample show detrital grains of Mesoproterozoic and Early Paleozoic ages, suggesting a maximum deposition age for the trench-fill sediment of -440 Ma. Also the U-Pb data confirmed-360 Ma overgrown rims that might have formed during the subduction zone epidote-amphibolite facies metamorphism. Reappraisal revealed that the Kitomyo Schist is not the oldest high-pressure type schist in Japan and rather comparable to the Late Paleozoic Renge Metamorphic Rocks and their equivalents in the Kurosegawa Belt. The Devono-Carboniferous high-pressure metamorphic rocks in Japan might have been paired with their coeval batholiths along the 'Greater South China' margin that was extensively eroded during later tectonic processes. (C) 2020 Elsevier B.V. All rights reserved.

<p>The Motai-Matsugataira Belt (MMB) in the eastern margin of the northeastern Japan arc comprises Paleozoic metamorphic complexes. The high-P Yamagami metamorphic rocks in the belt are subdivided into the high-grade Yamagami I and low-grade Yamagami II units. The Yamagami I metamorphic rocks consist mainly of pelitic schist, epidote amphibolite, and garnet amphibolite. The occurrence of paragonite in rutile and the chemistry of amphiboles indicate that the Yamagami I metamorphic rocks underwent the highest-grade metamorphism in the MMB. Phengite K-Ar ages of the pelitic schists and amphibolitesindicateexhumation during 322 to 287 Ma. These petrological and geochronological results for the Yamagami metamorphic rocks indicate that part of the MMB is probably an extension of the Renge Belt of southwestern Japan.</p>