Hydrogeochemical zoning of uranium isotopes (²³⁴U/ ²³⁸U) in the Southern Siberian paleocontinent: the role of the South Baikal reservoir in the groundwater formation

Abstract

The southern deformed edge of the Siberian paleocontinent is studied for zoning the disturbance of 234 U/ 238 U cyclic equilibrium in groundwaters discharged to the accreted Khamardaban terrane. A relationship is established between vertical variations of 234 U/ 238 U (ОА4/8) activity ratios and the hydrogeochemical zoning of groundwaters. Lateral ОА4/8 zoning of groundwaters in the basement rocks and sedimentary cover of the Siberian platform is described. It is emphasized that an important role is played by the water propagating from the South Baikal reservoir (SBR) (ОА4/8 = 1.95-1.99; U content = 0.44-0.46 μg/L) under the shore of Lake Baikal. It is suggested that the lateral advancement of the SBR water is facilitated by the development of low-angle (weakened by rifting) fractures of the Angara thrust fault, as well as subvertical fractures in the shear zone of the Main Sayan Fault. Monitoring data on the study area show that the ratios of the groundwaters components vary in time due to Cherdyntsev-Chalov deformational effect, chemical interaction of the waters and evaporites, and mixing of the groundwaters with contrasting hydrogeochemical signatures.

Integrated Monitoring of Hazardous Geological Processes in Pribaikalye: Pilot Network and First Results

“…7). Этот состав соответствует окисленному компоненту байкальской воды [Rasskazov et al, 2020b]. Компонент 2 с минимальным значением ОА4/8 при минимальной концентрации U (максимальное значение 1/U) представлен водой среднего течения р. Бугульдейка в полосе Geodynamics & Tectonophysics 2022 Volume 13 Issue 5 Seminsky K.Zh.…”

“…Диаграмма ОА4/8 -1/U поверхностных и подземных вод окрестностей пункта «Бугульдейка». Состав глубинной воды ЮБР (Южно-Байкальского резервуара) и OКБВ (окисленного компонента байкальской воды с повышенным содержанием U, квадрат) показан по работе [Rasskazov et al, 2020b]. Станции 10, 117 и 136 обозначают совокупности точек неоднократных измерений проб подземных вод (см.…”

“…Diagram ОА4/8 -1/U for surface water and groundwater in the vicinity of "Buguldeika" station. The composition of deep water in SBR (South Baikal reservoir) and of OCBW (oxidized component of the Baikal water with high U content, square) is reported in [Rasskazov et al, 2020b]. Stations 10, 117 and 136 represent the sets of points of repeated measurements of groundwater samples (see Fig.…”