Quantitative phase petrology of cordierite–orthoamphibole gneisses and related rocks |
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| Authors: | J F A DIENER R POWELL R W WHITE |
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| Institution: | 1. School of Earth Sciences, The University of Melbourne, Melbourne, Victoria 3010, Australia (johann.diener@uct.ac.za);2. Present address: Department of Geological Sciences, University of Cape Town, Private Bag, Rondebosch 7701, South Africa.;3. Institute of Geosciences, University of Mainz, D‐55099 Mainz, Germany |
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| Abstract: | Cordierite–orthoamphibole gneisses and rocks of similar composition commonly contain low‐variance mineral assemblages that can provide useful information about the metamorphic evolution of a terrane. New calculated petrogenetic grids and pseudosections are presented in the FeO–MgO–Al2O3–SiO2–H2O (FMASH), Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O (NCKFMASH) and Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 (NCKFMASHTO) chemical systems to investigate quantitatively the phase relations in these rocks. Although the bulk compositions of cordierite–orthoamphibole gneisses are close to FMASH, calculations in this system do not adequately account for the observed range of mineral assemblages. Calculations in NCKFMASH and NCKFMASHTO highlight the role of minor constituents such as Ca, Na and Fe3+ in the mineral assemblage evolution of such rocks and these systems are more appropriate for interpreting the evolution of natural examples. |
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| Keywords: | anthophyllite ferric iron gedrite NCKFMASHTO pseudosection whiteschist |
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