R8: Metamorphic rocks and tectonics

[R8-12] Non-barometric behaviour of Na pyroxenes in blueschist-facies metamorphic rocks

*Wataru J Yabuta¹, Takao Hirajima² (1. Non, 2. Kyoto Univ.)

Keywords:Na pyroxene, Blueschist , Geobarometry, Schreinemakers’ analysis

We report chemical compositions of Na pyroxenes in blueschist facies metamorphic rocks in the Kurosegawa Belt in Kyushu, Japan. They are characterised by low Di component and microscopic variation (Xjd = 0.2 – 0.6) within hand-specimen size. Of the constraints, the coexisting Na amphibole is notable as it effectively reduces Jd contents of Na pyroxene, even when coexisting quartz and albite. In this sense, Jd contents are detached from pressure in blueschist facies.