STABLE ISOTOPIC CONSTRAINTS ON THE NATURE OF THE SYNTECTONIC FLUID REGIME OF THE CANADIAN CORDILLERA

Oxygen, hydrogen and carbon isotopic analyses of rocks from the Canadian Cordillera document regional variations in the origins and evolution of crustal fluids. High temperature systems in unmetamorphosed, felsic volcanic rocks are characterized by low delta-O-18 values. Veins in regional metamorphic rocks are characterized by delta-O-18 values that reflect approximate oxygen isotopic equilibration of the fluids with regional rock units. The delta D studies indicate that both systems were dominated by meteoric water. The delta-C-13 values for vein carbonate indicate a regional lithologic control on delta-C-13 values. The data indicate that convection of surface fluids to depths of 10 or more kilometers during orogenesis was common. The existence of deep convection cells involving meteoric water further indicates that fluid pressures to these depths must have been approximately hydrostatic. Regional structural style appears to exert an important control on the depth of penetration of surface fluids.