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Igneous and High-Grade Metamorphic Rocks in the Kurosegawa Tectonic Zone and Its Tectonic Significance

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  • Chemistry
  • Earth Science


Journal of Geosciences, Osaka City University Vol. 28, Art. 2, p. 45-83 March, 1985 Igneous and' High-Grade Metamorphic Rocks in the Kurosegawa Tectonic Zone and Its Tectonic S'ignificance Shin-ichi YosHIKURA* (With 10 Figures and 2 Tables) Abstract This article presents the results of geological and petrological research on the igneous and high-grade metamorphic rocks of the Kurosegawa Tectonic Zone and discusses their bearing on t,he tectonic evolution of the Kurosegawa Zone in pre圃Siluriantime. The Siluro-Devonian silicic pyroclastic rocks including welded tuff were probably forn1ed by highly explosive eruptions of vesiculating silicic magma and were deposited on land (welded tuff) or in shallo'¥v marine environment not so far from the land (other tuff lithologies). -The pres- ence of the reef limestone interstratified with the Siluro-Devonian sequence also suggests the deposition in a shallow marine environment, while the abundant elastic materials derived from the granitic rocks in the silicic pyroclastic rocks and limestone require a nearby terr1genous source (either continent or matured island arc). On the basis of the mode of occurrence, the granitic rocks can be divided into the pre-Silurian granite (so called “Mitaki igneous rocks”) and the Devonian granite. The former was unconform- ably covered by the Siluro田Devoniansequence, whereas the later was intruded into it. Since the remarkab1le contrasts with respect to the petrography and petrochemistry can be recognized between these granites, tectonic setting of the emplacement of these granites may be different. Probably, the pre圃Siluriangranite can be regarded as representing the rock suite em- placed in the compressional tectonic setting and may have been formed in relation to the high- grade metamorphism. On the contrary, the Devonian granite may be the subvolcanic equivalents of the Siluro・Devoniansilicic volcanics emplaced in the extentional tectonic settmg. A, the high-grade metamorp

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