V. Yu. Lavrushin

Travertines of the northern Caucasus

Mineralogical and isotope-chemical characteristics of carbonate travertines of the Greater Caucasus are investigated. It is shown that concentrations of many chemical elements, which predominantly precipitate together with iron hydroxides, decrease along the strike of the travertine dome. At the same time, δ13C and 18O values in carbonates systematically increase due to kinetic effects of isotope fractionation. This leads to the formation of isotopically heavy calcite (δ13C up to 16.3‰) near the travertine dome base. Concentrations of other elements (Mg, Sr, Ba, Na, S, and Li), which form a isomorphic part of calcite crystal lattice, almost do not change along the strike of the dome. Comparison of concentrations of these elements in travertines and initial water solutions makes it possible to get ideas on trends of their redistribution in the carbonate-water system. Correlations found in this work define not only TDS content and concentration of some ions, but also REE spectra and formation temperatures of ancient fluid systems.

Formation of Mud-Volcanic Fluids in Taman (Russia) and Kakhetia (Georgia): Evidence from Boron Isotopes

Temperatures of the formation of mud-volcanic waters are determined based on concentrations of some temperature-dependent components (Na–Li, Mg–Li). Estimates obtained for the Taman and Kakhetia regions are similar and range from ∼ 45 to ∼170°С, which correspond to depths of ∼1–4.5 km. The calculated temperatures correlate with the chemical (Li, Rb, Cs, Sr, Ba, B, I, and HCO3) composition of water and δ13С (СО2) and δ13С (CH4) values in spontaneous gases. The isotope values indicate that mechanisms of the formation of δ13С-rich gases, i.e., gases with high δ13С values (up to +16.0‰ in СО2 and –23.4‰ in CH4) in mud-volcanic systems of Taman and Kakhetia are governed by fluid-generation temperatures rather than the supply of abyssal gases. The δ11В value was determined for the first time in mud-volcanic products of the Caucasus region. This value ranges from +22.5 to +39.4‰ in the volcanic water of Georgia, from –1.2 to +7.4‰ in the clayey pulp of Georgia, and from –7.6 to +13.2‰ in the clayey pulp of Taman. It is shown that the δ11В value in clay correlates with the fluid-generation temperature and δ11В correlates with δ13С in carbon-bearing gases. These correlations probably testify to the formation of different phases of mud-volcanic emanations in a single geochemical system and suggest the crucial role of temperature in the development of isotope-geochemical features.

Isotopic Composition of Thermal Waters in Chukotka

Twenty three groups of thermomineral springs in eastern Chukotka with the discharge temperature of 2 to 97°C and mineralization of 1.47 to 37.14 g/l are studied and compared with surface freshwater from their localities. The δD and δ18O values in surface waters vary from −121.4 to −89.5‰ and from −16.4 to −11.1‰, respectively, while respective values in thermomineral waters range from −134.2 to −92.5‰ and from −17.6 to −10.5‰. The δD value in surface waters decreases from the east to west, i.e., toward interior areas of the peninsula. Hydrothermal springs most depleted in deuterium (δD < −120‰) are localized in the geodynamically active Kolyuchinskaya-Mechigmen Depression. According to the proposed formation model of Chukotka thermomineral waters, their observed chemical and isotopic characteristics could result from the mixing (in different proportions) of surface waters with the deep-sourced isotopically light mineralized component (δD ≈ −138‰, δ18O ≈ −19‰, M = 9.5−14.7 g/l). The latter originates most likely from subpermafrost waters subjected to slight cryogenic metamorphism.

Recent tectonomagmatic reactivation of the Kolyuchino-Mechigmen zone of the Chukchi Peninsula from data on the composition of gases in hydrothermal springs

Thirty-three groups of thermal mineral springs in the Chukchi Peninsula are studied. The thermal fluids of the Kolyuchino-Mechigmen Zone (KMZ) show specific characteristics. The zone corresponds to recent depression with occurrences of basic volcanism and high seismicity. Characteristic features of the gases in the springs of the KMZ include the predominance of carbon dioxide, high percentage of mantle-derived helium, enrichment of CO2 in 13C, admixture of nonatmospheric nitrogen, excess in 40Ar and 15N relative to the atmosphere, maximal depletion of thermal water in deuterium and heavy oxygen isotope, and the highest estimates of deep temperature in reservoirs of hydrothermal fluid. All these features indicate the contemporary ascent of a mantle diapir that supplied helium enriched in 3He and thermal energy to the crust, thus provoking thermal metamorphism of rocks and degradation of permafrost.

Waters from mud volcanoes of Azerbaijan: Isotopic-geochemical properties and generation environments

New data on chemical and isotopic properties of waters from 35 mud volcanoes of Azerbaijan show that they are represented by two contrasting types characterized by different mineralization: Cl-Na (M = ∼30–80 g/L) and HCO3-Cl-Na (M = ∼8–15 g/L). Waters of the last type are usually enriched with alkaline metals, B, and Br. Waters of the Cl-Na type are similar in their Cl/Br coefficient with seawater. According to Mg-Li and Na-Li geothermometers, waters were formed at temperatures varying from ∼20 to ∼140°C. Taking into consideration these estimates, “roots” of the volcanoes under consideration should be located at depths of 6.0–7.5 km. The fluid generation temperatures exhibit a tendency for their growth toward the Greater Caucasus orogen. The δD, δ18O, and δ13C (TDIC) values in dissolved inorganic carbon vary from −32 to −12 and −0.6 to +10.4‰ (V-SMOW) or −12.9 to +37.3‰ (V-PDB), respectively. The highest δD, δ18O, and δ13C values are typical of HCO3-Na waters. It is shown that the growth of formation (Mg-Li) temperatures is accompanied by a significant increase of the δ18O(H2O) and δ13C(HCO3−) values along with HCO3− concentrations. The degree of water enrichment with Br, B, and alkaline metals also increases. This allows the formation of soda waters from mud volcanoes with elevated 18O and 13C contents to be attribute to relatively high-temperature transformations of mineral and organic matter during the catagenic alteration sedimentary rocks.

Physicochemical Model for the Generation of the Isotopic Composition of the Carbonate Travertine Produced by the Tokhana Spring, Mount Elbrus Area, Northern Caucasus

AbstractThe isotopic composition of calcite from travertine deposits of the Tokhana-Verkhnii hot spring in the Elbrus area shows broad variations in δ13C and δ18O (from +3.8 to +16.3‰ and from +24.6 to +28.1‰, respectively). The δ13C and δ18O values increase toward the sole of the travertine dome. The isotopically heaviest carbonates (δ13C of up to +16.3‰) were found near the bottom of the dome and composed ancient travertine, which are now not washed by mineral water. The scatter of the δ13C values of the fresh sample is slightly narrower: from +3.8 to +10‰. Calculations indicate that all carbonates of the Tokhana dome were not in equilibrium with spontaneous carbon dioxide released by the spring (

Isotope and chemical composition of gases from mud volcanoes in the Taman Peninsula and problem of their genesis

\delta ^{13} C_{CO_2 }

Isotopic-geochemical peculiarities of gases in mud volcanoes of eastern Georgia

= −8‰). To explain the generation of isotopically heavy travertine, a physicochemical model was developed for precipitation of Ca carbonates during the gradual degassing of the mineral water. The character of variations in the calculated δ13C values (from +5.5 to +13‰) is in good agreement with the tendency in the variations of the δ13C in the carbonate samples. The calculated and measured pH values are also consistent. Our results demonstrate that the isotopic composition of large travertine masses can be heterogeneous, and this should be taken into account during paleoclimatic and paleohydrogeological reconstruction.