『Abstract
　In situ Li analyses of 4348 to 3362 Ma detrital zircons from the Jack Hills, western Australia by SIMS reveal that the Li abundances (typically 10 to 60 ppm) are commonly over 10,000 times higher than in zircons crystallized from mantle-derived magmas and in mantle-derived zircon megacrysts (typically <2 ppb). High Li concentrations in zircons (10 to 250 ppm) have also been found in igneous zircons from three continental parent rocks: granites, Li-rich pegmatites, and migmatites in pelitic metasediment. The substitution of trivalent cations (REEs and Y) in zircon correlates with Li⁺¹ and P⁺⁵, suggesting that an interstitial site for Li, as well as the xenotime substitution for P, provides charge balance for REEs. Li is thus fixed in the zircon structure by coupled substitutions, and diffusive changes in [Li] composition are rate-limited by slow diffusion of REEs. The Jack Hills zircons also have fractionated lithium isotope ratios (δ⁷Li=-19 to +13‰) about five times more variable than those recorded in primitive ocean floor basalts (2 to 8‰), but similar to continental crust and its weathering products. Values of δ ⁷Li below -10‰ are found in zircons that formed as early as 4300 Ma. The high Li compositions indicate that primitive magmas were not the source of Jack Hills zircons and the fractionated values of δ⁷Li suggest that highly weathered regolith was sampled by these early Archean magmas. These new Li data provide evidence that the parent magmas of ancient zircons from Jack Hills incorporated materials from the surface of the Earth that interacted at low temperature with liquid water. These data support the hypothesis that continental-type crust and oceans existed by 4300 Ma, within 250 million years of the formation of Earth and the values of δ⁷Li suggest that weathering was extensive in the early Archean.

Keywords: zircon; Jack Hills; lithium; weathering; continental crust; Hadean』

1. Introduction
2. Samples
3. Analytical methods
　3.1. Standards for Li analysis by ion microprobe
　3.2. Li isotopic ratio and Li abundance
　3.3. Li ion imaging
4. Results
5. Discussion
　5.1. Li substitution in zircon
　5.2. Evaluation of variable Li compositions in the Jack Hills zircon suite
　5.3. Low δ⁷Li: evidence for weathering of the early Archean crust
6. Conclusions
Acknowledgments
Appendix A. Supplementary data
References