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Integrated Fe and Li isotopes constrain fractional crystallization and fluid-magma interaction in the formation of unzoned Li-mineralized pegmatites
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DOI：10.1016/j.gca.2026.07.042.png)
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Abstract
En 中文
The roles of fractional crystallization and fluid–magma interaction in the genesis of unzoned Li-mineralized pegmatites remain debated. Because Fe and Li isotopes fractionate differently among melts, crystals, and fluids, their combined systematics offer a powerful means to discriminate between these processes. In this study, we report major and trace elemental and O, Fe and Li isotopic data for the Li-mineralized and barren pegmatites and associated leucogranites in the Ke’eryin field, Songpan–Ganzi orogenic belt, eastern Tibet. Lithium-mineralized pegmatites have TFe2O3, REE, and K/Rb lower than those in barren pegmatites, and both are lower than those in leucogranites. These correlations are consistent with origin of Li-mineralized pegmatites as products of more extreme fractional crystallization. Additionally, both Li-mineralized and barren pegmatites have stronger tetrad effects (TE1,3 > 1.1), lower Nb/Ta (< 5) and Zr/Hf (< 26) than leucogranites, indicating fluid involvement in their evolution. Both pegmatite types have δ56Fe values (0.13–0.20‰ and 0.00–0.28‰, respectively) similar to those of leucogranites (0.04–0.23‰). Lithium-mineralized pegmatites have δ7Li values (−0.8–+1.8‰ vs. −1.8–+1.9‰) similar to those of leucogranites, whereas barren pegmatites show higher δ7Li values (−1.5–+5.4‰). Nevertheless, both pegmatite types display a negative correlation between Li contents and δ7Li values. No correlation is observed between O and Fe isotopes or between O and Li isotopes in either Li-mineralized or barren pegmatites, indicating that external fluids and wallrocks did not modify their isotopic signatures.
Keywords:
Unzoned Li-mineralized pegmatites
Fluid–magmainteraction
Fractional crystallization
Fe isotopes
Li isotopes
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