Contributions to Mineralogy and Petrology

, Volume 114, Issue 4, pp 510–518 | Cite as

Two-feldspar geothermometry: a review and revision for slowly cooled rocks

  • Herbert Kroll
  • Christos Evangelakakis
  • Gerhard Voll


Recent improvements in the experimental and thermodynamic basis of two-feldspar geothermometry allow one to recover temperatures of coexistence more reliably. Some problems, however, persist: (1) the experimental solvi by Seck (1971a) and Elkins and Grove (1990) differ from each other; (2) it is not known to what extent Na−K−Ca exchange equilibrium is approached; (3) both solvi are probably metastable with regard to Al, Si order; (4) it is difficult to judge how closely high-temperature natural feldspars compare to this situation; (5) the thermodynamic treatment neglects phase transformations; (6) the temperature dependence of the Margules parameters used to model non-ideal mixing behaviour may not be linear; (7) it is not clear which expressions should be used to describe ideal activities. With these caveats in mind we treat the problem of retrograde resetting in high-grade metamorphic rocks that were slowly cooled under essentially dry conditions. Coexisting feldspars from such rocks commonly do not plot on a common isotherm. Thus temperatures derived from such pairs using any of the proposed two-feldspar geothermometers will necessarily be in error. We suggest that the non-equilibrium compositions result from retrograde intercrystalline K−Na exchange. This exchange continues after the plagioclase and alkali feldspar have already become essentially closed systems with respect to Al−Si exchange, which is a prerequisite for (Na,K)−Ca exchange. We use a modified version of the Fuhrman and Lindsley (1988) programme to reverse the K−Na exchange and derive concordant temperatures.


Mineral Resource Close System Metamorphic Rock Recent Improvement Thermodynamic Basis 
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Copyright information

© Springer-Verlag 1993

Authors and Affiliations

  • Herbert Kroll
    • 1
  • Christos Evangelakakis
    • 1
  • Gerhard Voll
    • 2
  1. 1.Institut für MineralogieWestfalische Wilhelms-UniversitätMünsterGermany
  2. 2.Institut für MineralogieUniversität zu KölnKoln 1Germany

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