Lithium isotopes are a potential tracer of silicate weathering but the relationship between lithium isotope compositions and weathering state still need to be established with precision. Here, we report Li concentrations and Li isotope compositions of soils developed along a 4 million year humid-environment chronosequence in the Hawaiian Islands. Li concentrations are variable with depth and age, ranging from 0.24 to 21.3 ppm, and significant Li depletions (up to 92%) relative to parent basalts are systematically enhanced towards the surface. Our calculations show that the relative contribution from atmospheric deposits to the Li soil budget remains small, with a maximum contribution from dust Li of 20% at the oldest site. This is explained by the capacity of the weathering products to retain, within the profiles, the Li coming from basalt alteration, and allows us to explore more specifically the role of alteration processes on soil Li isotope signatures. The delta Li-7 values display a large range between -2.5 parts per thousand and + 13.9 parts per thousand. The youngest soils (0.3 ka) display the same delta Li-7 value as fresh basalt, regardless of depth, despite similar to 30% Li loss by leaching, indicating that there is little Li isotope fractionation during the incipient stage of weathering. delta Li-7 values for the older soils (>= 20 ka) vary non-linearly as a function of time and can be explained by progressive mineral transformations starting with the synthesis of metastable short-range order (nano-crystalline) minerals and followed by their transformation into relatively inert secondary minerals. Results highlight significant Li isotope fractionation during secondary mineral formation and in particular during Li uptake by kaolinite. Finally, we suggest that the non-monotonous evolution of the regolith delta Li-7 value over the last 4 Ma is consistent with climatic variations, where congruent release of Li isotopes occurs during warmer periods. (C) 2014 Elsevier Ltd. All rights reserved.