By comparing high-quality volcanic gas and whole rock compositions, we calculated the apparent (observed) mass partition coefficients Kd* for 58 elements on six basaltic volcanoes located in arc and rift/hotspot settings. The inferred Kd* vary from � 1100 for sulfur to 0.0001 for zirconium, i.e., within seven orders of magnitude. Only 14 elements have Kd* > 1, including highly volatile S, Se, Te and halogens, as well as Tl, Re, Os, Bi, Cd, Au, In and As. Alkali metals have Kd* in the rangefrom 0.1 for Cs to 0.01 for Na. Partition coefficients of other rock-forming elements are <0.001. The partition coefficients for elements depend on element speciation and concentrations of ligand-forming elements in the gas such as sulfur and chlorine.
Elements transported in the gas predominantly as halides have higher partition coefficients in HCl-rich arc gases, whereas elements preferably forming sulfides, hydrides and free atoms, have higher Kd* in sulfur-rich, HCl-poor and reduced rift/hot-spot gases. Degassing directly from the free melt surface is negligible; deep gas passing through the erupting vent is quickly overwhelmed by the signal of low-pressure degassing. Equilibration of rising bubbles with the surrounding melt almost eliminates the difference between Kd* calculated for degassing lava flows (no connection with deep magma) and for lava lakes and open-vent volcanoes (convective mass exchange with deep magma takes place). Diffusion does not strongly affect the apparent partitioning of magmas degassing at surface. Gas bubbles growing in near-surface silicate melts at atmospheric pressure have a large density difference compared to the surrounding melt of 12–15 thousand times. This leads to the rapid expansion of such bubbles and a decrease in the thickness of the diffusion boundary layer in the melt due to its stretching around the growing bubble, which sharply decreases diffusion fractionation. As a result, the apparent partition coefficients (Kd*) for degassing basaltic volcanoes are close to the equilibrium ones (Kd) for most of the elements. The partition coefficients of volatile elements (S and Cl) calculated from the comparison of volcanic gas and rock compositions are in agreement with the values determined previously via experiments or theoretical modeling.

Скважинами глубиной до 3000 м у подножья действующих вулканов Корякский и Авачинский в пределах Авачинской депрессии вскрыты минерализованные воды (до 22 г/л общей минерализации) с температурой около 60°С в западной части разведанной области и холодные — восточнее, ближе к Тихоокеанскому побережью. В статье приведены литературные, фондовые и собственные данные по химическому и изотопному составу этих вод. Состав вод хлоридно-натриевый, с очень низкими содержаниями сульфата и магния и с высоким — кальция, и необычно высокой концентрацией стронция. Содержание свободного газа примерно 50 мл/л. В газе преобладают метан и азот (примерно 70 и 30 об.%, соответственно), присутствует сероводород (около 30 мг/л) и очень мало СО2 (< 0.5 об.%). Отношение N2/Ar, как правило, выше воздушного, т. е. присутствует неатмосферный азот. Обсуждаются возможные варианты взаимодействия вода-порода, ответственные за химический состав вод, и предлагается концептуальная модель предполагаемого бассейна минеральных вод, включающая положение возможных источников тепла и минерализованных растворов.

Saline waters (up to 22 g/l) were tapped by deep (to 3000 m) wells at the foot of active volcanoes Avachinsky and Koryaksky, within Avachinsky depression. Temperature of waters was ~ 60°C in the western part and cold in the eastern part, closer to the Pacific coast. In this paper we present the literature and our own data on chemical and isotopic composition of these waters. The waters are of the Na-Cl type with extremely low abundances of sulfate and magnesium, high concentration of calcium and surprisingly high concentration of strontium. The waters contain about 50 ml/l of gas where methane and nitrogen are main components (~ 70 vol% and 30 vol%, respectively) and also presents H2S (~ 30 ml/l) and very low concentrations of CO2 (< 0.5 vol%). The N2/Ar ratio, as a rule, is higher than the air ratio, i.e., the non-atmospheric nitrogen presents. We discuss the possible options of the water-rock interaction, responsible for the chemical composition of waters, and offer a conceptual model of the proposed basin of mineral waters that includes the distribution of deep temperatures, the location of the possible sources of heat mineralized solutions.