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Glaucophane and pyroxene breakdown reactions in the Pennine units of the Eastern Alps
Author(s) -
HOLLAND T. J. B.,
RAY N. J.
Publication year - 1985
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1985.tb00328.x
Subject(s) - pyroxene , blueschist , actinolite , geology , glaucophane , greenschist , geochemistry , metamorphism , albite , chlorite , mineralogy , olivine , paleontology , eclogite , epidote , subduction , tectonics , quartz
New occurrences of crossite and jadeitic pyroxene are described from a thick metabasite unit within the upper levels of the Peripheral Schieferhülle in the Tauern Window, Austria. Unusual textures are preserved which provide evidence for the reactions and mechanisms involved in the breakdown of crossite and jadeitic pyroxene. Zones of albite and chlorite, produced by reaction between crossite and paragonite, have been preserved due to sluggish reaction kinetics during decompression from the blueschist to the greenschist facies. The zonal sequence is interpreted in terms of chemical potential gradients in Na, Mg and Al, which have been established by overstepping the equilibrium boundary. Breakdown textures of jadeite‐acmite pyroxene to a symplectite of albite + hematite + actinolite, and of crossite to talc and actinolite are also described. The occurrence of crossite and jadeitic pyroxene at high levels within the Peripheral Schieferhülle implies that even upper levels of the structural sequence have undergone blueschist facies metamorphism with pressures in excess of 8 kbar during the Alpine collisional event.