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https://hdl.handle.net/2440/34314
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Type: | Journal article |
Title: | Calculated phase equilibria in K₂O-FeO-MgO-Al₂O₃-SiO₂-H₂O for silica-undersaturated sapphirine-bearing mineral assemblages |
Other Titles: | Calculated phase equilibria in K(2)O-FeO-MgO-Al(2)O(3)-SiO(2)-H(2)O for silica-undersaturated sapphirine-quartz-bearing mineral assemblages |
Author: | Kelsey, D. White, R. Powell, R. |
Citation: | Journal of Metamorphic Geology, 2005; 23(4):217-239 |
Publisher: | Blackwell Publishing Ltd |
Issue Date: | 2005 |
ISSN: | 0263-4929 1525-1314 |
Statement of Responsibility: | D. E. Kelsey, R. W. White and R. Powell |
Abstract: | Silica-undersaturated, sapphirine-bearing granulites occur in a large number of localities worldwide. Such rocks have historically been under-utilized for estimating P–T evolution histories because of limited experimental work, and a consequent poor understanding of the topology and P–T location of silica-undersaturated mineral equilibria. Here, a calculated P–T projection for sapphirine-bearing, silica-undersaturated metapelitic rock compositions is constructed using THERMOCALC for the FeO-MgO-Al2O3-SiO2 (FMAS) and KFMASH (+K2O + H2O) chemical systems, allowing quantitative analysis of silica-undersaturated mineral assemblages. This study builds on that for KFMASH sapphirine + quartz equilibria [Kelsey et al. (2004) Journal of Metamorphic Geology, vol. 22, pp. 559–578]. FMAS equilibria are significantly displaced in P–T space from silicate melt-bearing KFMASH equilibria. The large number of univariant silica-undersaturated KFMASH equilibria result in a P–T projection that is topologically more complex than could be established on the basis of experiments and/or natural assemblages. Coexisting sapphirine and silicate melt (with or without corundum) occur down to c. 900 °C in KFMASH, some 100 °C lower than in silica-saturated compositions, and from pressures of c.≤1 to ≥12 kbar. Mineral compositions and composition ranges for the calculated phases are consistent with natural examples. Bulk silica has a significant effect on the stability of sapphirine-bearing assemblages at a given P–T, resulting in a wide variety of possible granulite facies assemblages in silica-undersaturated metapelites. Calculated pseudosections are able to reproduce many naturally occurring silica-undersaturated assemblages, either within a single assemblage field or as the product of a P–T trajectory crossing several fields. With an understanding of the importance of bulk composition on sapphirine stability and textural development, silica-undersaturated assemblages may be utilized in a quantitative manner in the detailed metamorphic investigation of high-grade terranes. |
DOI: | 10.1111/j.1525-1314.2005.00573.x |
Published version: | http://dx.doi.org/10.1111/j.1525-1314.2005.00573.x |
Appears in Collections: | Aurora harvest Earth and Environmental Sciences publications |
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