Phosphorus – an omnipresent minor element in garnet of diverse textural types from leucocratic granitic rocks |
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| Authors: | K Breiter M Novák F Koller J Cempírek |
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| Institution: | (1) Czech Geological Survey, Praha, Czech Republic;(2) Institute of Geological Sciences, Masaryk University, Brno, Czech Republic;(3) Department of Geological Sciences, University of Vienna, Vienna, Austria |
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| Abstract: | Summary Elevated P contents of up to 0.086 apfu (1.21 wt.% P2O5) were found in garnet from leucocratic granitic rocks (orthogneisses, granites, barren to highly evolved pegmatites) in the
Moldanubicum and Silesicum, Czech Republic, and in complex granitic pegmatites from southern California, USA, and Australia.
Minor concentrations (0.15–0.55 wt.% P2O5) appear ubiquitous in garnet from leucocratic granitic rocks of different origins and degrees of fractionation. Concentrations
of P are not related to Mn/(Mn + Fe) that vary from 0.12–0.86 and to textural types of garnet (i.e., isolated anhedral to
euhedral grains and nodules, graphic and random garnet–quartz aggregates, subsolidus veins of fine-grained garnet). Garnet
compositions exhibit negative correlations for P/Si and P/R2+ where R2+ = Fe + Mn + Mg + Ca, while Al is constant at ∼2.05 apfu. Concentrations of Na are largely below 0.02 apfu but positively correlate with P. The main substitution may involve A-site vacancy and/or the presence of some light element(s) in the crystal structure. The substitution □P2 R2+ −1Si−2 and/or alluaudite-type Na□P3 R2+ −1Si−3 seem the most likely P-incorporating mechanisms. The partitioning of P among garnet and associated minerals in granitic systems
remains unclear; however, it directly affects the distribution of Y and REEs. |
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