Using calculated chemical potential relationships to account for coronas around kyanite: An example from the Bohemian Massif

P. Stipska, R. Powell, R. W. White, J. A. Baldwin

Research output: Contribution to journalArticlepeer-review

54 Scopus citations

Abstract

Corona textures around kyanite, involving for example zoned plagioclase separating kyanite from the matrix, reflect the instability of kyanite with the matrix on changing P-T conditions, commonly related to decompression. The chemical potential gradients set up between the kyanite and the matrix as a consequence of slow Al diffusion drive corona development, with the zoning of the plagioclase reflecting the gradients. Calculated mineral equilibria are used to account for corona textures involving plagioclase ± garnet around kyanite, and replacement of kyanite by plagioclase + spinel symplectite, in quartz + plagioclase + K-feldspar + garnet + kyanite granulite facies gneiss from the Blanský les massif in the Bohemian massif, Czech Republic. In the garnet-bearing coronas, a commonly discontinuous garnet layer lies between the kyanite and the continuous plagioclase layer in the corona, with both the garnet and the plagioclase appearing mainly to replace matrix rather than kyanite. The garnet layer commonly extends around kyanite from original matrix garnet adjacent to the kyanite. Where garnet is missing in the corona, the kyanite itself may be replaced by a spinel. -plagioclase corona. In a local equilibrium model, the mineral and mineral compositional spatial relationships are shown to correspond to paths in μ(Na2O)-μ(CaO)-μ(K2O)-μ(FeO)-μ(MgO)-μ(SiO2) in the model chemical system, Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2 (NCKFMAS). The discontinuous nature of the garnet layer in coronas is accounted for by the effect of the adjacent original garnet on the chemical potential relationships. The replacement of kyanite by spinel + plagioclase appears to be metastable with respect to replacement by corundum + plagioclase, possibly reflecting the difficulty of nucleating corundum.

Original languageEnglish
Pages (from-to)97-116
Number of pages20
JournalJournal of Metamorphic Geology
Volume28
Issue number1
DOIs
StatePublished - Jan 2010

Keywords

  • Bohemian massif
  • Chemical potential
  • Ky-K-feldspar granulite
  • Plagioclase ± garnet around kyanite
  • Plagioclase-spinel symplectite

Fingerprint

Dive into the research topics of 'Using calculated chemical potential relationships to account for coronas around kyanite: An example from the Bohemian Massif'. Together they form a unique fingerprint.

Cite this