Chemical geothermometry: application to mud volcanic waters of the Caucasus region

Abstract

The generation temperatures of gas-water fluids released from mud volcanoes in different provinces of the Caucasian region have been constrained using Mg/Li (TMg/Li) chemical geothermometry. Mud volcanic fluids in the Taman Peninsula (Kerch-Taman mud volcanic province) were generated at temperatures (TMg/Li) from 41°C to 137°C. The depths of the respective mud reservoirs estimated from TMg/Li values and local geothermal gradient are in a range of 1.0 to 3.4 km which spans the Maykop Formation of marine shale. For the South Caspian province, the TMg/Li values of waters vary from 18°C to 137°C and the respective root depths HMg/Li of mud volcanoes range from ∼ 0.85 to 6.5 km. The obtained TMg/Li values for the analyzed mud volcanic waters from Caucasian provinces are in positive correlation with HCO3− contents and water oxygen isotope compositions ( ${\delta ^{18}}{{\text{O}}_{{{\text{H}}_{\text{2}}}{\text{O}}}}$ and $\Delta {\delta ^{18}}{{\text{O}}_{{{\text{H}}_{\text{2}}}{\text{O}}}}$ ) and in high negative correlation with Cl−. The increase of TMg/Li toward the Greater Caucasus Range, as well as the lateral TMg/Li patterns in the Taman and South Caspian mud volcanic provinces, support the idea that mud volcanic fluids generate at temperatures increasing progressively toward the Alpine orogenic belt.