2016/02/05 by Christophe Ballouard, Marc Poujol, Philippe Boulvais +4 · 3 citations
Computer Science · Earth and Planetary Sciences · #Art #Geochemistry and Geologic Mapping #Geological and Geochemical Analysis #Geology #High-pressure geophysics and materials #Humanities #Hydrothermal circulation #Paleontology
paper · doi:10.1130/g37475.1
openalex publication_date 2016/02/05 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/04
In their late stages of evolution, peraluminous granitic melts exsolve large amounts of fluids which can modify the chemical composition of granitic whole-rock samples. The niobium/tantalum (Nb/Ta) ratio is expected to decrease during the magmatic differentiation of granitic melts, but the behavior of both elements at the magmatic-hydrothermal transition remains unclear. Using a compilation of whole-rock geochemical data available in the literature, we demonstrate 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.