Lithium Isotope Geochemistry in Geological Systems

Lithium has two stable isotopes, 6Li and 7Li, whose relative proportions in minerals and fluids record processes ranging from mantle melting and crustal differentiation to fluid–rock interaction at Earth’s surface. Variations in δ7Li, expressed in per mil relative to a standard, reflect isotope fractionation during high‐temperature crystallisation, low‐temperature aqueous transport and diffusion in solid phases. In mantle and arc settings, Li isotopes trace the balance between slab‐derived input, mantle melting degrees and intracrustal differentiation, while in volcanic and plutonic systems they can reveal post‐eruptive mobility and fluid exsolution. In sedimentary basins, Li enriched by weathering of Li‐rich magmatic rocks accumulates in closed brine systems under arid conditions. Analytical advances in multi‐collector ICP‐MS and SIMS now allow sub‐per mil precision on small samples, facilitating studies of zircons, biotite, olivine, quartz and fluid inclusions. Globally, lithium isotope geochemistry informs our understanding of ore deposit formation, geothermal circulation, magma plumbing and crust–mantle recycling.

Research from Nature Portfolio

Studies of global arc magmas demonstrate that primitive arc basalts have Li/Y ratios similar to mid-ocean ridge basalts, indicating limited slab contribution to Li enrichment. Instead, low degrees of sub-arc mantle melting combined with extensive intracrustal differentiation in thickened continental arcs enhance Li contents of arc magmas. Weathering of these enriched crustal sources then generates high-Li brines in extensional basins under arid climates. In volcanic rock suites, post-eruptive diffusion during slow cooling can modify both Li concentration and δ7Li in phenocrysts, decoupling magmatic signatures from erupted compositions. Recognition of this mobility is essential for robust petrogenetic interpretations. Experimental and field studies of ophiolitic chromitite-bearing mantle sequences reveal extremely large Li isotope heterogeneity at small scales, indicating that subducted slab fluids impart highly variable Li compositions to melts interacting with the overlying mantle wedge. These results highlight the need to account for both diffusive and source-related fractionation when using Li isotopes to trace deep-Earth processes.

Lithium Isotope Geochemistry in Geological Systems publication trend

The graph below shows the total number of articles in lithium isotope geochemistry in geological systems across all publications each year (not limited to Nature Index journals).

Technical terms

Isotope fractionation: The partitioning of isotopes between phases or compounds due to differences in mass, resulting in measurable δ‐values.

δ7Li: The per mil deviation of the 7Li/6Li ratio in a sample relative to a standard, indicating isotopic enrichment or depletion.

Intracrustal differentiation: The process by which a magma evolves chemically through crystal fractionation and melt segregation within the crust.

Sub-arc mantle melting: Partial melting of the mantle wedge above a subducting slab, influenced by fluid release from the slab.

Brine deposits: Lithium-rich saline waters concentrated in closed basins, typically in arid climates, which serve as major economic sources of Li.

References

1. Geochemical significance of lithium and boron isotopic heterogeneity evolving during the crystallization of granitic melts. Geology (2023).
2. High‐precision determination of lithium and magnesium isotopes utilising single column separation and multi‐collector inductively coupled plasma mass spectrometry. Rapid Communications in Mass Spectrometry (2017).
3. Post-eruptive mobility of lithium in volcanic rocks. Nature Communications (2018).
4. Lithium systematics in global arc magmas and the importance of crustal thickening for lithium enrichment. Nature Communications (2020).
5. Extremely large fractionation of Li isotopes in a chromitite-bearing mantle sequence. Scientific Reports (2016).
6. Processes controlling lithium isotopic distribution in contact aureoles: A case study of the Florence County pegmatites, Wisconsin. Geochemistry Geophysics Geosystems (2010).
7. Biotite as a recorder of an exsolved Li-rich volatile phase in upper-crustal silicic magma reservoirs. Geology (2022).