Experimental partitioning of Li between zircon and different silicate melts: implications for Li contents in the Hadean and modern crust

The Li concentrations in natural zircons vary by over six orders of magnitude, and Li intra-zoning within zircon has been used to model temperature–time histories in the crust, where the inputs to these T–t models presume some initial Li content of intra-zircon domains. This potential wealth of information may be further improved with experimental studies that characterize Li partitioning between zircon and melt. Here we report experiments that systematically quantify Li partitioning between zircon and different silicate melts as a function of temperature. We also explored how Li in zircon is structurally accommodated and the possible element(s) that influence Li incorporation. Zircon–melt partitioning is reported in four different melt compositions, with ASI values (molar ratio of Al 2 O 3 /(Na 2 O + K 2 O + CaO)) ranging from 0.56 to 1.44. The experiments were performed in a piston–cylinder device at 1000, 1100, 1200, and 1300 °C, and at a constant pressure of 1 GPa. Results of experiments show that the zircon–melt Li partition coefficient is not dependent on melt composition, but shows a negative relationship to temperature. This means the large range of Li concentrations in natural zircon is probably due to the combined factors of crystallization temperature and the original melt Li contents. We used our data to derive an empirical equation to describe the relationship of Li partitioning between zircon and melt (D Li ) and temperature ( K ): log 10 (D Li ) = (5918 ± 1479)/ T − (6.91 ± 1.05). Through experiments with or without P added to the starting rock mix, we found that P-doped experiments yield lower D Li than those without P, which implies that Li competes with P for rare earth element (REE 3+ ) charge balance. To test the influence of H 2 O content of the melt on Li partitioning in zircon, we also explored melts with varying H 2 O contents (nominally 0, 5 wt.%, and 10 wt.%); results indicate that Li partitioning in zircon is not dependent on the H 2 O content of the melt. This method lays the groundwork to estimate the concentration of Li in melt that crystallized zircon, given the concentration of Li in zircon and an independent temperature estimate, provided that no post-crystallization modification of Li in zircon has occurred. We applied this equation to Hadean, Archean, and modern zircons and found that the predicted [Li] melt for Jack Hills zircons, Archean TTG and sanukitoid are one order magnitude higher than the modern crust.