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Conference papers
Nb-Ta fractionation in peraluminous granites: a marker of the magmatic-hydrothermal transition
Abstract : In their last stages of evolution (i.e. at the
magmatic-hydrothermal transition), peraluminous
granitic melts exsolve a large amounts of fluids
which can modify the chemical composition of
whole-rock granitic samples and lead to the
deposition of economicaly significant mineralization
(Sn, W).
Nb and Ta are lithophile elements considered to
be “geochemical twins” because they have the same
charge and a similar ionic radius. However, Nb/Ta
ratios are highly variable in granites. Some authors
have demonstrated that the Nb/Ta ratios decrease in
granites during fractional crystallization [1]. Other
studies have suggested that Nb and Ta could be
fractionated in evolved peraluminous granites during
the interaction with late magmatic fluids [2].
In this study [3], we demonstrate, using a
compilation of whole-rock geochemical data
available in the litterature that fractional
crystallization alone is not sufficient to explain the
distribution of Nb-Ta in most peraluminous granites.
However, we notice that most of the granitic samples
displaying evidence of interactions with fluids have
Nb/Ta < ∼5. We propose that the decrease of the
Nb/Ta ratio in evolved melts is the consequence of
both fractional crystallization and sub-solidus
hydrothermal alteration. We suggest that the Nb/Ta
value of ~5 fingerprints the magmatic-hydrothermal
transition in peraluminous granites. Furthermore, a
Nb/Ta ratio of ~5 appears to be a good marker to
discriminate mineralized from barren peraluminous
granites.
https://hal-insu.archives-ouvertes.fr/insu-01369015
Contributor : Isabelle Dubigeon <>
Submitted on : Tuesday, September 20, 2016 - 2:00:34 PM
Last modification on : Thursday, January 14, 2021 - 11:43:30 AM
Contributor : Isabelle Dubigeon <>
Submitted on : Tuesday, September 20, 2016 - 2:00:34 PM
Last modification on : Thursday, January 14, 2021 - 11:43:30 AM