Phase equilibria modelling of blueschist and eclogite from the Sanbagawa metamorphic belt of south-west Japan reveals along-strike consistency in tectonothermal architecture

Weller, O. M. and Wallis, S.R. and Aoyoa, M. and Nagaya, T. (2015) Phase equilibria modelling of blueschist and eclogite from the Sanbagawa metamorphic belt of south-west Japan reveals along-strike consistency in tectonothermal architecture. Journal of Metamorphic Geology, 33. pp. 579-596. ISSN 0263-4929 DOI 10.1111/jmg.12134

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Abstract

The Sanbagawa metamorphic belt of southwest Japan is one of the type localities of subduction-related high-P metamorphism. However, variable pressure–temperature (P–T) paths and metabasic assemblages have been reported for eclogite units in the region, leading to uncertainty about the subduction zone paleo-thermal structure and associated tectonometamorphic conditions. To analyse this variation, phase equilibria modelling was applied to the three main high-P metabasic rock types documented in the region – glaucophane eclogite, barroisite eclogite and garnet blueschist – with modelling performed over a range of P, T, bulk rock H2O and bulk rock ferric iron conditions using thermocalc. All samples are calculated to share a common steep prograde P–T path to similar peak conditions of ∼16–20 kbar and 560–610 °C. The results establish that regional assemblage variation is systematic, with the alternation in peak amphibole phase due to peak conditions overlapping the glaucophane–barroisite solvus, and bulk composition effects stabilizing blueschist v. eclogite facies assemblages at similar P–T conditions. Furthermore, the results reveal that a steep prograde P–T path is common to all eclogite units in the Sanbagawa belt, indicating that metamorphic conditions were consistent along strike. All localities are compatible with predictions made by a ridge approach model, which attributes eclogite facies metamorphism and exhumation of the Sanbagawa belt to the approach of a spreading ridge.

Item Type: Article
Uncontrolled Keywords: NILAREP;
Subjects: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Journal or Publication Title: Journal of Metamorphic Geology
Volume: 33
Page Range: pp. 579-596
Identification Number: 10.1111/jmg.12134
Depositing User: Sarah Humbert
Date Deposited: 15 Mar 2017 13:49
Last Modified: 10 Apr 2017 17:37
URI: http://eprints.esc.cam.ac.uk/id/eprint/3843

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