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Major and trace elements of the saline fluids at the Outokumpu deep drilling site - the role of the hydrolysis of rocks and fluid inclusions

Paleofluids in the Outokumpu Deep Drill Hole are characterized by high salinities and high homogenization temperatures in excess of 330 oC. Fluid inclusions in addition to an aqueous phase contain also gaseous phases such as CO2 und CH4. Cationic radii of the dissolved salts are higher than seawater with Li/Na ratios in deeper parts of the hole indicating the influence of magmatic water. Stable isotope (dD, d18O) signatures point to an metamorphic origin of the Paleofluids. Deep ground waters in the Outokumpu crystalline basement deviate significantly from in their stable isotope ratios from fluid inclusions plotting to the left of the global meteoric water line in a dD - d18O diagram. This suggests that they may have formed as a mixture of meteoric and saline waters. In addition, Cl/Br and Na/Br ratios point to chemical exchange with serpentinite host rocks of the Outokumpu Formation. Many models have been proposed to account for the enhanced salinity of deep ground waters and the shift in the stable isotopes, but our data gathered so far indicate that the saline fluid are derived primarily through water–rock interaction. The role of fluid inclusions as important contributors to the saline fluids is unsupported so far.