Geochemical features of Sakhalin Island mud volcanoes

Abstract

The study, based on a complex geochemical research, found that the composition of the most chemical elements in mud breccia from the Yuzhno-Sakhalinsky (YSMV) and Pugachevsky (PMV) mud volcanoes (Sakhalin Island), the unique phenomena of endogenous defluidization in the Hokkaido-Sakhalin fold system (alpine-type folding), are comparable to Clarke (C) contents of these elements (0.8-1.2xC). For Na. Li, Zn and Sn, the ratio between the ele­mental contentsand their Clarke values (Csampe/Clarke value) vary from 1.4 to 5.2xC. But the increased contents of Na and Li are due to the ascending endogenous fluid revealed. Study of the mud breccia chemical composition changes in different explosive activity of YSMV under the seismic activity variations allowed to establish that, when the mud-volcanic gryphons are activated against the background of increase in the temperature of the water-mud mix­ture and the emission of spontaneous gases, the contents of a number of elements (iron, calcium, manganese, rare earth elements, etc.) are decreased. This is explained by the formation of soluble hydrocarbonate complexes. Dagin­skie gasgeothermal system (DGHS) trace elements depleted ooze samples were compared with YSMV and PMV samples and exposed that the high ratios of Csample/Clarke values for the majority of elements do not exceed 0.6xC. Ooze samples from DGHS having higher elemental contents than Clark contents were observed only for Cd content (2.2-3.4xC) and Pb (0.7-J .5xC). Analysis of diatom flora on the DGHS site indicates the existence of an active fluid dynamic system that drains oil and gas bearing complexes. The factors determining the "weighting" of the methane carbon isotope composition in the southern part of Sakhalin Island are the increased seismic activity of deep-seated faults, as well as the presence of intrusions (diabase) and metamorphically altered rocks.