『Abstract
Calculations based on a KMnFMASH petrogenetic grid derived using
an internally consistent thermodynamic dataset indicate that the
principal effect of the presence of Mn in average subaluminous
pelite compositions is to stabilize garnet to higher and lower
pressures and temperatures over a wide range of bulk compositions.
Garnet-bearing fields expand to lower temperatures and pressures
with the addition of Mn, and garnet appears as an extra phase
at low pressures . The addition of Mn also increase the number
and extent of four AMnFM phase assemblages and stabilizes five
AMnFM phases along univariant reactions. The KMnFMASH system predictions
for typical subaluminous pelite bulk compositions match the sequence
of isograds and assemblages observed in the Barrovian zones. The
sequence of assemblages observed in the Stonehaven section can
also be predicted if there is variation in bulk composition within
the stratigraphic section. Mn appears to be less important in
producing the sequence of isograds and garnet-absent assemblages
in the low-pressure Buchan zones. The addition of Mn to the calculations
does not change the sequence of isograds that are predicted to
be stable in a regional metamorphic terrane, but the P-T position
of these isograds does change. In particular, the predicted temperature
of the garnet-in isograd is lowered by as much as 100゜C by the
addition of Mn to KFMASH. Mn also increases the range of metapelite
bulk compositions that develop the assemblages traditionally identified
as metapelite isograds.
Key words: Barrovian, Buchan, garnet, KMnFMASH, pelite.』
Introduction
Method
Data generation of Mn end-members
Result
A petrogenetic grid
Pressure-temperature-composition (P-T-X) diagrams
Discussion
Comparison with previous workers
Comparison with natural assemblages: the Eastern Highlands
Comparison with natural assemblages: the Tono contact aureole
Effects of other components
Conclusions
Acknowledgements
References
Appendix 1
Mineral pairs
Appendix 2
Thermodynamic properties
Appendix 3
Mineral formulae, end-members and compositional variables