On deep circulation of meteoric waters within Baikal Rift

Abstract

Anomalies in pore water (PW) composition have been found in the 100 m-long core BDP-93 that was drilled in Southern Lake Baikal, in four piston cores taken from the same region, and in recent sediments from Frolikha Bay, a hydrothermal vent site in Northern Lake Baikal. PW anoma- lies are manifested as significant increases in concentrations of sulphates, bicarbonates, chlorides, and the ions of alkali and alkali-earth metals, in some cases, in the appearance of specific minor elements. These increases are recorded at sin- gle depths within a core. Anomalies were found at different depths below the sediment-water interface (from centimetres to tens of meters) and the level of pore water enrichment by these components varies from station to station. Anomalies have specific features in each of the lake basins. It is shown that there is a genetic relationship between sub-aquatic and terrestrial centres of thermal-water discharge in Northern Lake Baikal. PW data obtained in Frolikha Bay exemplify a sub-aquatic hydrothermal water discharge occur- ring in the lake. These anomalous PW concentrations pre- sumably are due to the leaching of ambient sediments. In ad- dition, some fraction of the sulphates, halogens, and minor elements may have multiple geneses, including the input of fluids from deep zones of the earth's crust and mantle that oc- cur through the fault system in areas of tectonic breakdowns. In Southern Lake Baikal, in the Selenga River delta, ground waters of specific composition that are relics of an- cient salt lakes could serve as a source of anomalous concen- trations in PW components. Their influence may be realized through the extensive zones of increased permeability. Effect of "vagabonding sieves" could contribute to the penetration of water fluids through friable deposits, including clay-rich sediments. This effect may be of great importance in the seismically active Baikal rift zone.