SOURCES OF SALINITY IN CRYSTALLINE ROCKS; THE ROLE OF CRYOGENIC PROCESSES ASSOCIATED WITH PERMAFROST CONDITIONS AND PROXIMITY OF CONTINENTAL ICE SHEETS

Crystalline rock environments worldwide compose a considerable mass of the Earth’s near surface (<40 km) continental mass. Most of these rocks are billions of years old and are associated with limited porosity. The pore spaces are dominated by fluids and gases that are often described as highly saline and under considerable pressure. Both Ca- and Na- Cl brines with salinities in excess of 100 grams per litre contain considerable quantities of methane and other gases. Numerous theories of the evolution and origin of these fluids have been argued over the past 30 years. The rocks contain salinity bearing mineral phases and highly saline fluid inclusions that contribute many elemental components to the fluids upon weathering. The isotopic compositions of hydrogen and oxygen of crystalline fluids are unique compared to saline fluids in sedimentary and surficial environments.

However, controversy still exists as to the role of cryogenic processes to create highly saline fluids in these environments. Many crystalline rock terrains, particularly in the northern hemisphere have undergone repeated episodes of glaciations and permafrost in the recent past. In many areas today, such as Antarctica and the northern islands of Canada very saline fluids and brines are common in near surface conditions. However, recent studies in permafrost terrains of northern Canada and Greenland (associated with the glacial ice sheet) have found very limited evidence of highly saline groundwater and surface waters. These findings in modern perglacial-glacial environments along with hydrogeological evidence do not appear to support a cryogenic option for the evolution of saline crystalline fluids.