Effect of F-B-H2O on Zr diffusion in granitic melts: Implications for Zr mineralization
These data are supplementary data for the manuscript entitled "Effect of F-B-H2O on Zr diffusion in granitic melts: Implications for Zr mineralization". As a critical strategic metal, zirconium (Zr) is commonly associated with granitic rocks enriched in H2O, F and B. Nevertheless, the individual and coupled effects of these volatiles on Zr diffusion remain poorly constrained, limiting our mechanistic understanding of Zr magmatic enrichment. Here, we conducted systematic zircon dissolution experiments using a piston-cylinder apparatus at 0.5 GPa and 1173–1673 K to determine the Zr diffusion coefficient in granitic melts with variable volatile concentrations as well as melt compositions. Our results demonstrate that Zr diffusion coefficients in hydrous peralkaline melts are ~4 times higher than those in hydrous metaluminous and peraluminous melts. In single-volatile peralkaline melts, both F and H2O monotonically enhance the Zr diffusion coefficient, whereas B exerts a non-monotonic control on Zr diffusion. In multi-volatile systems with coexisting F, B, and H2O, the enhancement of the Zr diffusion coefficient was significantly weaker than the direct linear superposition of individual volatile effects. Single-volatile behaviors are governed by distinct melt dissolution mechanisms of each volatile species, while coupled volatile effects arise from mutually dependent speciation that modulates melt polymerization. The high Zr diffusion coefficient in B-bearing granitic melts provides a kinetic support for the preferential occurrence of Zr mineralization in low-B peralkaline granites rather than high-B pegmatites. Diffusion‑limited crystal growth modeling further indicates that multi‑volatile (F-B-H2O) melts produce significantly larger zircon grains than H2O‑only melts under identical magmatic conditions.