Disentangling the compositional variations of lawsonite in blueschist-facies metasediments (Schistes Lustrés, W. Alps)

Lawsonite is important as a carrier of H2O in subduction zones and as a petrological tracer. The trace-element content of lawsonite in mafic rocks has been used as a record of fluid–rock interactions but has received less attention in metamorphosed oceanic sediments. This study documents the major, and trace-element composition, together with 87Sr/86Sr isotopic ratios, of the different lawsonite types identified in the upper units of the Schistes Lustrés complex of the Western Alps, a paleo-accretionary prism of the Liguro-Piemont slow-spreading ocean subducted up to 40 km. The lawsonite-rich upper units of the Schistes Lustrés complex are principally composed of metamorphosed pelitic sediments and carbonates. Lawsonite content reaches 40 vol.