EVIDENCE FROM STABLE CHLORINE ISOTOPES FOR MULTIPLE SOURCES OF CHLORIDE IN GROUNDWATERS FROM CRYSTALLINE SHIELD ENVIRONMENTS

摘要

Analyses of the ~(37)Cl/~(35)Cl isotopic ratio of Canadian and Fennoscandian Shield groundwaters show a range of values, as well as several interesting trends. The data seem to indicate several different sources of Cl in these environments and a variety of common processes which may be invoked to account for the observed trends. In particular, Canadian Shield groundwaters have a dominantly negative ~(37)Cl/~(35)Cl isotopic signature range from -0.51 to +0.17. Fennoscandian groundwaters, from a wide range of geological and geographical locations, are dominated by positive isotopic signatures and a range of values from -0.61 to +1.97. Similar to results for major ions and for~ 2H and ~(18)O, individual study sites on each Shield have distinctive ~(37)Cl/~(35)Cl signatures for the most concentrated brines. However, shallower groundwaters in Finland appear to be mixtures of dilute glacial waters and possible Baltic-Eem Sea end members with local brines. The ability to distinguish Cl sources and understand mixing scenarios in these environments promises to add a valuable tool to understanding hydrogeological and geochemical processes in fractured rock media.