Experimental breakdown of staurolite plus inclusions of albite and muscovite at 800 degrees C and 0.1 GPa

Abstract

Experimental breakdown of staurolite + inclusions of albite and muscovite (representing an aluminous Fe-rich metapelitic composition) occurs within the KNFMASH system at 800 degrees C and 0.1 GPa under fluid-present conditions over periods of 2 days to 8 weeks. The overall melt-producing reaction is staurolite + muscovite + plagioclase + vapour = hercynite + corundum + mullite + quartz + liquid, and involves three reactions; staurolite + vapour = hercynite + corundum + quartz + liquid, albite + vapour = mullite + liquid, and muscovite + vapour = mullite + liquid. Melt (glass) compositions are siliceous (77.2-64.5 wt.% SiO2), peraluminous (A/CNK = 1.5-5.5), and have granite-trondjhemite compositions in terms of normative Ab-Ab-Or contents. Textures indicate that quartz formed later than corundum. The corundum + quartz + hercynite assemblage after staurolite is considered to be metastable and only likely to be found in nature where staurolite-bearing rocks have undergone rapid heating and melting followed by quenching.