Partitioning of Nb and Ta between rutile and felsic melt and the fractionation of Nb/Ta during partial melting of hydrous metabasalt |
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Authors: | Xiaolin Xiong Hans Keppler Huaiwei Ni Yuan Li |
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Affiliation: | a Laboratory of Metallogenic Dynamics, Guangzhou Institute of Geochemistry, CAS, 510640 Guangzhou, China b Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany |
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Abstract: | In order to fully assess the role of rutile in fractionation of Nb/Ta during partial melting of hydrous metabasalt, we have measured rutile - felsic melt partition coefficients (D values) for Nb and Ta with tonalitic to trondhjemitic compositions at 1.5-3.5 GPa, 900-1350 °C and ∼5.0-20 wt% H2O. DNb, DTa and DNb/DTa range from 17 ± 1 to 246 ± 13, 34 ± 2 to 232 ± 25 and 0.51 ± 0.04 to 1.06 ± 0.13, respectively. For the compositions investigated, melt composition appears to have no observable effect on the partitioning; the effect of pressure is also slight; whereas temperature and H2O have marked effects. DNb, DTa and DNb/DTa increase with decreasing temperature and H2O content, showing a reversal of DNb/DTa from <1.0 to >1.0. Using the data that approached equilibrium and obeyed Henry’s law, expressions describing the dependences of DNb, DTa and DNb/DTa on temperature, pressure and melt H2O content were obtained: |
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