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Anatectic vs. granite-derived origin of pegmatites from the Bihar Mica Belt (eastern India)-insights from fluid inclusion and mineral chemistry, and Li-isotope composition of micas.

Singh T, UpadhyayD, SahaR.

LITHOS

https://doi.org/10.1016/j.lithos.2026.108655 

This study constrains the petrogenesis of granitic pegmatites from the Bihar Mica Belt using mica trace element and Li isotope compositions,quartz-hosted fluid inclusion microthermometry and LA-ICP-MS analyses, integrated with phase equilibria, partial melting, and fractional crystallization modelling. Elevated δ⁷Li values in pegmatite micas indicate derivation from highly evolved granitic magmas. Collectively, the geochemical, isotopic, and modelling results demonstrate that extensive fractional crystallization was the dominantprocess governing the evolution and formation of the BMB granitic pegmatites.

Fig: Geological setting, petrography, geochemistry, and petrogenetic evolution of the Bihar Mica Belt pegmatites. (a) Simplified geological map. (b) Field photograph of pegmatite intruding schist, and (c) photomicrographs of the pegmatite (d) contains aqueous bi-phase fluid inclusions and chemistry of (e-g) fluid inclusion, mica, and Li isotope variations constrain pegmatite evolution, (h-i) Rayleigh fractional crystallization modelling.

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