R8: Metamorphic rocks and tectonics

[R8-09] Kinetic control on Al-Fe³⁺ distribution between Na-amphibole and Na-pyroxene in the lawsonite blueschist facies

*Wataru YABUTA¹, Takao HIRAJIMA² (1. Non, 2. Kyoto Univ.)

Keywords:Blueschist, Na-pyroxene, Na-amphibole, geobarometry

Al-Fe³⁺ distribution between coexisting Na-Px and Na-Amp has been investigated in lawsonite blueschist facies rocks. It is suggested that Al is concentrated in Na-Amp from metabasalts preserving igneous texture, while Al is distributed equally in metacherts and veins, where the two minerals formed in simultaneous crystallization. These findings clearly show an limit of Jd-Qtz-Ab barometry and introduces a new point of view: rock texture, in interpreting chemical compositions of minerals.