Geochemistry and origin of saline groundwaters in the Fennoscandian Shield

摘要: Chemical and isotopic analyses of water from drill holes mines throughout the Fennoscandian Shield show that distinct layers groundwater are present. An upper layer fresh is underlain by several sharply differentiated saline layers, which may differ in salinity, relative abundance solutes, O, H, Sr S isotope signature. Saline can be classified into four major groups based on geochemistry presumed origin. Brackish waters 50–200 m depth coastal areas around Baltic Sea exhibit marine chemical fingerprints, modified reactions with host rocks. These represent relict Holocene seawater. Inland, three types observed: an uppermost brackish 300–900 depth; brines 1000–2000 superdeep have been observed to a at least 11 km hole Kola Peninsula, U.S.S.R. Electrical seismic studies shield suggest such commonly present even greater depths. The salinity all inland groundwaters attributed predominantly water-rock interaction. main solutes Cl, Ca, Na Mg varying proportions, depending rock lithology. dissolved gases increases but varies site site. gas components N2, CH4 (up 87 vol.%) locally H2. δ13C value for methane highly variable (−25 −46%), it suggested hydrothermal or metamorphic trapped within surrounding rocks most obvious source CH4. has meteoric oxygen-hydrogen compositions, whereas values deeper plot above line, indicating considerably longer mean residence time effective low temperature equilibration Geochemical results some localities demonstrate cannot formed through simple mixing between deep rather independent itself not satisfactorily verified although contain significant proportion Precambrian fluids.