The Influence of Hydrothermal Activity on the Li Isotopic Signature of Rivers Draining Volcanic Areas

We explore the geochemistry and the isotopic composition of lithium (δ7Li) of rivers draining volcanic islands (Guadeloupe, Iceland, Java, Martinique and Sao Miguel) with a specific focus on continental hydrothermal activity. Our preliminary results reveal a global-scale trend between δ7Li and the elemental ratio Li/Na in rivers draining volcanic islands. We suggest that this trend results from a mixture between waters with low δ7Li and high Li/Na, inherited from high-temperature water rock interactions, and waters with low Li/Na and high δ7Li, in which Li is controlled by the neoformation of clays during low-temperature chemical weathering in basaltic soils. This latter process can be described by a simple isotope fractionation model, consistent with reported values for isotopic fractionation factors between secondary weathering products and water.These data highlight the important potential role of continental high-temperature weathering processes on the oceanic budget of lithium.