Nb–Ta fractionation by partial melting at the titanite–rutile transition

John T, Klemd R, Klemme S, Pfaender JA, Hoffmann JE, Gao J (2011)

Publication Type: Journal article

Publication year: 2011

Journal

Contributions To Mineralogy and Petrology Springer Verlag (Germany)

Publisher: Springer Verlag (Germany)

Book Volume: 161

Pages Range: 35-45

DOI: 10.1007/s00410-010-0520-4

Abstract

During the evolution of the Earth, distinct geochemical reservoirs with different Nb/Ta ratios have developed. Archean granitoids of the tonalite-trondhjemite-granodiorite (TTG) suite, which represent the Earth's early continental crust, show larger Nb/Ta variations than any other Earth reservoir. This implies that significant Nb-Ta fractionation must have occurred during early crust formation, while the underlying mechanism behind is still unclear. Here, we present a new model on how Nb may be fractionated from Ta during partial melting of subducted oceanic crust. Our data show that Nb/Ta ratios in melts derived from rutile- and titanite-bearing eclogite are largely controlled by the modal relative abundances of rutile and titanite in the source. High modal ratios of titanite over rutile generate melts with very high Nb/Ta (>60), whereas low modal titanite/rutile produces melts with much lower Nb/Ta (≤30). Very low Nb/Ta (<16) occur when all Ti-phases are consumed at very high degrees of melting. As the modal ratio of titanite to rutile is a function of pressure, the Nb/Ta of melts is a function of melting depth. Our new model helps to explain the extreme variation of Nb/Ta observed in many TTGs and thus how Nb and Ta were fractionated during the early evolution of the Earth. Furthermore, the model also indicates that simple one-stage melting models for mafic crust are not sufficient to explain the formation of TTGs. © 2010 Springer-Verlag.

Authors with CRIS profile

Reiner Klemd Professur für Geochemie von Lagerstätten

Involved external institutions

Westfälische Wilhelms-Universität (WWU) Münster DE Germany (DE) Chinese Academy of Sciences (CAS) / 中国科学院 CN China (CN) Rheinische Friedrich-Wilhelms-Universität Bonn DE Germany (DE) Technische Universität Bergakademie Freiberg DE Germany (DE)

How to cite

APA:

John, T., Klemd, R., Klemme, S., Pfaender, J.A., Hoffmann, J.E., & Gao, J. (2011). Nb–Ta fractionation by partial melting at the titanite–rutile transition. Contributions To Mineralogy and Petrology, 161, 35-45. https://dx.doi.org/10.1007/s00410-010-0520-4

MLA:

John, Timm, et al. "Nb–Ta fractionation by partial melting at the titanite–rutile transition." Contributions To Mineralogy and Petrology 161 (2011): 35-45.

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