Is the Nb-Ta Fractionation a Marker of an Interaction with Fluids in Peraluminous Granites?

Abstract : In their last stage of evolution, highly evolved peraluminous melts can exsolve a significant amount of fluids which can change their chemical composition and lead to the deposition of mineralization. The Nb/Ta ratio is expected to decrease naturally during differentiation but the behavior of both elements at the magmatic-hydrothermal transition is still unclear. Here, we present a compilation of some of the whole rock geochemical data available in the literature for crustal peraluminous granites. We noticed that for low Nb/Ta values, most peraluminous granites display evidences of fluid interaction such as: a large increase of the highly incompatible element contents (Cs, Sn, F, Li, Rb, W), a significant increase of the Tetrad effect and a decrease of the K/Rb ratio to values as low as 150. We propose that the Nb/Ta values around 5 mark the magmatic-hydrothermal transition and that the decrease of the Nb/Ta ratio in highly evolved melts is the consequence of both fractional crystallization and sub-to post-solidus magmatic-hydrothermal alteration. We also propose that low Nb/Ta values can be used as markers to discriminate barren granites from mineralization-bearing granites.
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Contributor : Isabelle Dubigeon <>
Submitted on : Wednesday, August 19, 2015 - 1:59:30 PM
Last modification on : Wednesday, May 15, 2019 - 3:58:26 AM

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  • HAL Id : insu-01185205, version 1

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Christophe Ballouard, Marc Poujol, Philippe Boulvais, Yannick Branquet, Romain Tartèse, et al.. Is the Nb-Ta Fractionation a Marker of an Interaction with Fluids in Peraluminous Granites?. SGA2015: 13th Biennial meeting, Aug 2015, Nancy, France. pp.675-678. ⟨insu-01185205⟩

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