The Petrogenetic Grid and Subfacies for Middle-temperature Metapelites
- 1 February 1977
- journal article
- Published by Oxford University Press (OUP) in Journal of Petrology
- Vol. 18 (1) , 114-143
- https://doi.org/10.1093/petrology/18.1.114
Abstract
All a priori possible types of PT diagrams for medium-temperature quartz- and muscovite- bearing metapelites, are deduced theoretically on the base of analysis of the concentration diagram for the system SiO2-AI2O3-Fe2O3-FeO-MgO-CaO-K2O-Na2O-H2O. Comparisons with all known mineralogic observations permitted one to choose the most probable type of diagram for all those derived. PT calibration of this paragenetic grid is given as based on experimental data. It is established, that the Fe/Mg ratio decreases in minerals of all the univariant associations with increase of pressure. The same is true of divariant associations at constant temperature. The suggested new scheme of subfacies permits the detailing of estimates of the PT conditions for the medium-temperature region (in the first place with respect to pressure).Keywords
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