Hydrogarnet substitution in pyrope: a possible location for “water” in the mantle |
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| Authors: | L Ackermann L Cemi? K Langer |
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| Institution: | Institut für Mineralogie und Kristallographie, Technische Universität, D-1000 Berlin, Federal Republic of Germany |
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| Abstract: | Single-crystal spectra of pyropes, synthesized on the 3:1:3 composition of the system MgO-Al2O3-SiO2 atpH2O = ptotal = 25kbar and 1000°C, show a broad band centered at around 3400 cm?1 due toνH2O of (H2O)n aggregates in fluid inclusions and a sharp intense band near 3600 cm?1 due toνOH of (HO)44? clusters introduced by the hydrogarnet substitutionSi4+ = 4H+. The water contents in the synthetic pyrope, due to (HO)44? clusters are estimated near 0.05 wt.% H2O from spectroscopic data. Si deficits in microprobe analyses of the pyropes studied support the hydrogarnet substitution. These results show that the hydrogarnet substitution in pyrope may contribute to water contents in the mantle. |
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