Thallium behavior during high-pressure metamorphism in the Western Alps, Europe

Thallium (Tl) is a highly incompatible element which can be redistributed during various igneous and hydrothermal events such as mineral dehydration low-temperature alteration. Despite the strong influence fluid-rock interactions have on Tl redistribution importance of fluids in subduction-zone volatiles cycling, geochemical behavior high-P/T metamorphism has not yet been quantified. Here we provide new isotope composition (ε205Tl) concentration ([Tl]) data for suite 18 metapelite metacarbonate rocks from Schistes Lustrés Complex nearby Lago di Cignana exposure western Alps. This represents over range peak metamorphic P-T conditions 300–550 °C 1.5–3.0 GPa (similar to experienced most modern subduction zones). With increasing grade, [Tl] shows no statistical variation while ε205Tl initially remains fairly constant (in order Fraiteve (unit A) ε205Tlavg = −2.1 (± 0.3); Assietta B) −1.6 0.6); Albergian C) −1.9 0.5)) before shifting more negative values higher grade (Finestre D) −2.4 E) −3.5 0.3)). Although it appears likely that largely retained depths approaching those arc magma generation, mineralogical hosts change prograde devolatilization. may contribute significant shift related fractionation induced by only minor amounts loss due fluid-mineral partitioning. Prograde results breakdown chlorite other constituents, releasing chlorite-borne could part incorporated into phengite lost fluids. study emphasizes need reaction history considered studies retention or trace elements Tl.