The effect of Mn on mineral stability in metapelites revisited: new a–x relations for manganese-bearing minerals
MetadataShow full item record
This is the accepted version of the following article: White, R. and Powell, R. and Johnson, T. 2014. The effect of Mn on mineral stability in metapelites revisited: new a–x relations for manganese-bearing minerals. Journal of Metamorphic Geology. 32 (8): pp. 809-828, which has been published in final form at http://doi.org/10.1111/jmg.12095
The a–x relations recently presented in White et al. (2014, Journal of Metamorphic Geology, 32, 261–286) are extended to include MnO. This provides a set of internally consistent a–x relations for metapelitic rocks in the MnO–Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O2 (MnNCKFMASHTO) system. The mixing parameters for the Mn-bearing minerals were estimated using the micro-ϕ approach of Powell et al. (2014, Journal of Metamorphic Geology, 32, 245–260). Then the Mn-end-member thermodynamic properties were calibrated using a database of co-existing minerals involving literature data from rocks and from experiments on natural materials. Mn-end-members were calibrated for orthopyroxene, cordierite, staurolite, chloritoid, chlorite, biotite, ilmenite and hematite, assuming known properties for the garnet end-member spessartine. The addition of MnO to phase diagram calculations results in a marked expansion of the stability of garnet-bearing assemblages. At greenschist facies conditions garnet stability is extended down temperature. At amphibolite facies conditions, the garnet-in boundary shifts to lower pressure. While the addition of MnO greatly influences the stability of garnet, it has relatively little effect on the stability of other common metapelitic minerals, with the resultant diagrams being topologically very similar to those calculated without MnO. Furthermore, the addition of MnO in the amounts measured in most metapelites has only a small effect on the mode of garnet, with calculated garnet modes remaining smaller than 1% in the P–T range outside its predicted Mn-free P–T range.
Showing items related by title, author, creator and subject.
White, R.; Powell, R.; Holland, T.; Johnson, Tim; Green, E. (2014)New activity-composition (a-x) relations for minerals commonly occurring in metapelites are presented for use with the internally-consistent thermodynamic dataset of Holland & Powell (2011, Journal of Metamorphic Geology, ...
Thermobarometric constraints on pressure variations across the Plattengneiss shear zone of the Eastern Alps: Implications for exhumation models during Eoalpine subductionEberlei, T.; Johnson, Tim; White, R.; Roffeis, C.; Stüwe, K. (2014)Forward and inverse mineral equilibria modelling of metapelitic rocks in the hangingwall and footwall of the Plattengneiss, a major shear zone in the Eastern Alps, are used to constrain their tectonometamorphic evolution ...
Conductively driven, high-thermal gradient metamorphism in the Anmatjira Range, Arunta region, central AustraliaAnderson, J.; Kelsey, D.; Hand, M.; Collins, William (2013)LA-ICP-MS in situ U-Pb monazite geochronology and P-T pseudosections are combined to evaluate the timing and physical conditions of metamorphism in the SE Anmatjira Range in the Aileron Province, central Australia. All ...