LITHIUM ISOTOPES AS A TRACER OF FLUIDS IN REACTION ZONES OF THE CATALINA SCHIST

In the subduction-related Catalina Schist, reaction zones are developed at contacts of metamorphosed mafic blocks with chemically distinct mélange matrix. These reaction rinds exhibit complex chemical compositions some of which are the product of fluid-assisted metasomatic alteration. Bulk-rock lithium isotopic analysis was performed on samples collected along traverse profiles across the contacts between mafic blocks and their reaction rinds and in some cases into the matrix from different metamorphic grades, including amphibolite, lawsonite-blueschist, and lawsonite-albite facies in order to determine the role played by fluid-mediated processes in the Catalina Schist. Amphibolite facies traverses display gradational variations in Li concentrations and isotopic composition across these traverses with both Li concentrations and isotopic compositions elevated in the rinds compared to the block cores. There is a systematic variation in both Li concentration and isotopic composition moving into the blocks over distances of 5-10 cm. Lower-grade traverses exhibit sharp contrasts between block rind and matrix. Variations were limited to shorter distances of <4 cm. One-dimensional simple diffusion and advection-diffusion models were fit to the profiles that indicate that in some cases advection of fluids is required along with diffusion in order to best explain the observed variations.