Fluid infiltration effects on stable isotope systematics of the Susurluk skarn deposit, NW Turkey

摘要

A calcic skarn deposit occurs along the contact zone between Oligo-Miocene Qataldag Granitoid and Mesozoic limestones in Susurluk, northwestern Turkey. The skarn zone with little or no retrograde stage is represented by fluid inclusions with high homogenization temperatures (up to >600 °C) and a wide range of salinity (12 to >70 wt.% NaCl). Pluton-derived fluids facilitated occurrence of continuous pro-grade reactions in the country rocks (particularly in the proximal zone) and oxygen isotopic depletion in calc-silicate and calcite minerals. δ~(18)O of anhydrous minerals within proximal and distal zones indicate that skarn-forming fluids had a magmatic origin. The δ~(18)O values are 5.93-9.08‰ (mean 6.8‰) for garnet, 4.08-9.94‰ (mean 6.4‰) for pyroxene, 4.89-7.92‰ (mean 6.4‰) for wollastonite and 6.65-8.28‰ (mean 7.5‰) for vesuvianite. Temperatures estimated by isotopic compositions of mineral pairs are significantly lower than those measured from the fluid inclusions, indicating that isotopic equilibrium is not preserved between the skarn minerals. δ~(18)0 and δ~(13)C values are systematically depleted from marbles to skarn carbonates. Calc-silicate forming reactions and permeability increase triggered by volatilization and consequent strong infiltration of H_2O-rich siliceous fluids into the system promoted fluid-rock interaction causing isotopic resetting and isotopic depletion of silicates (e.g. pyroxene and wollastonite) and skarn calcites.