Aragonite and omphacite-bearing metapelite from Besshi region, Sambagawa belt in central Shikoku, Japan and its implication |
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Authors: | Yui Kouketsu and Masaki Enami |
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Institution: | Department of Earth and Planetary Sciences, Nagoya University, Nagoya 464-8601, Japan (email: ) |
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Abstract: | Aragonite and omphacite-bearing metapelite occurs in the albite–biotite zone of the Togu (Tohgu) area, Besshi region, Sambagawa metamorphic belt, central Shikoku, Japan. This metapelite consists of alternating graphite-rich and graphite-poor layers that contain garnet, phengite, chlorite, epidote, titanite, calcite, albite, and quartz. A graphite-poor layer contains a 1.5-cm ivory-colored lens that mainly consists of phengite, calcite, albite, and garnet. Aragonite, omphacite, and paragonite occur as inclusions in the garnet of the ivory lens. The aragonite has a composition that is close to the CaCO3 end-member: the FeCO3 and MnCO3 components are both less than 0.3 mol% and the SrCO3 component is about 1 mol%. The aragonite + omphacite + quartz assemblage in garnet indicates equilibrium conditions of P > 1.1–1.3 GPa and T = 430–550°C. Quartz grains sealed in garnet of the aragonite and omphacite-bearing sample and other metapelites in the Togu area preserve a high residual pressure that is equivalent to the Sambagawa eclogite samples. These facts suggest that: (i) the Togu area experienced eclogite facies metamorphism; and (ii) thus, eclogite facies metamorphism covered the Sambagawa belt more extensively than previously recognized. |
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Keywords: | aragonite eclogite facies omphacite Raman spectroscopy Sambagawa belt |
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