PALEO-HYDROGEOLOGY OF LATE PROTEROZOIC UNITS OF SOUTHEASTERN CANADIANCORDILLERA

A comprehensive geological and geochemical investigation of veining an d other manifestations of fluid flow in late Proterozoic units of the Windermere Supergroup in the southeastern Canadian Cordillera was unde rtaken to characterize the nature of hydrogeological systems during an d following deformation of a fold and thrust belt. The results of flui d inclusion studies document vein formation from moderate to low tempe rature, low salinity, aqueous fluids. Results of delta(18)O studies of vein quartz and carbonate indicate that the veins formed from fluids with high delta(18)O values, which in most cases were derived from ext ensive isotopic exchange between the fluids and Proterozoic units. In widespread, small, early, bedding-parallel veins and in larger subvert ical veins in units of biotite greenschist or higher metamorphic grade s, delta D values of inclusion fluids are generally > -90 permil indic ating vein formation from fluids originating from metamorphic devolati lization. In rocks of metamorphic grade less than biotite greenschist facies, larger, late tectonic, subvertical veins have delta D values ( -120 to -150 permil) for inclusion fluids indicative of vein formation from deeply circulated meteoric water. Results of delta(13)C and Sr-8 7/Sr-86 studies of vein carbonates indicate a marked degree of regiona l heterogeneity, which is related to variations in the host rock litho logy. Most significant are the unusually low delta(13)C (-11 to -17 pe rmil) and high Sr-87/Sr-86 (0.750 to 0.780) values of vein carbonate f rom the Old Fort-Point Formation. The close linkage of the delta(13)C and Sr-87/Sr-86 values of vein carbonate to lithology of the host unit indicates relatively rapid reequilibration of the isotopic signatures of dissolved C and Sr, as the fluids moved from one unit to another. Comparison of the results of this study to results obtained on a simil ar study of paleo-hydrogeology of extensional regimes of the southern Omineca Belt of the Canadian Cordillera indicates that in compressiona l regimes the depth of penetration of surface fluids is shallower and more heterogeneous. As a result, convected surface fluids in compressi onal regimes are in general cooler, have lower CO2 contents, and proba bly lower integrated total fluxes.