The generation of quartz-normative melts and corundum-bearing restites by crustal anatexis: petrogenetic modelling based on an example from the Lewisian of North-West Scotland |
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Authors: | I CARTWRIGHT A C BARNICOAT |
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Institution: | Department of Geology, University College of Wales, Aberystwyth, Dyfed SY24 3DB, Wales |
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Abstract: | Abstract Rare layers of an aluminous, muscovite-rich rock from the Lewisian Complex at Stoer, North-West Scotland, display evidence which suggests that the rock has undergone local partial melting to form quartz-bearing veins and a corundum-bearing restite. The assemblages observed in these rocks match those predicted by modelling in the system KAlO2-NaAlO2-Al2O3-SiO2-H2O (KNASH) where certain bulk compositions melt peritectically to give corundum-bearing restites and quartz-normative melts. Study of the model system shows that the observed parageneses could have formed from a range of bulk compositions with a variety of possible values of a H2O which could have been internally or externally buffered. The KNASH petrogenetic grid, together with another in the system CaO-Na2O-FeO-Al2O3-SiO2-H2O (CNFASH), allows the P–T path of the rocks to be delineated and an estimate to be made of the conditions at the peak of metamorphism as > 11 kbar and 900-925°C. This estimate is in agreement with P–T estimates using thermobarometric methods on adjacent lithologies: The activity of H2O in the system throughout metamorphism is calculated to have been >0.3. |
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Keywords: | Key-words: anatexis corundum-bearing restites Lewisian metamorphism petrogenetic modelling Scotland |
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