GEOCHEMISTRY OF SYNTECTONIC, CRUSTAL FLUID REGIMES ALONG THE LITHOPROBE SOUTHERN CANADIAN CORDILLERA TRANSECT

In conjunction with the Lithoprobe southern Canadian Cordillera progra m, an extensive examination of geochemical indicators of origins, move ment, chemical evolution, and economic significance of paleocrustal fl uids was conducted. The study area covers approximately 360 000 km(2) from the Canadian Rockies to Vancouver Island. Research incorporated p etrological, mineralogical, fluid-inclusion, epsilon(18)O, delta D, de lta(13)C, and Rb/Sr studies of samples of quartz +/- carbonate veins a nd other rock types. The results of the study document a variety of pr e-, syn-, and postorogenic, crustal fluid events. In the Rockies, a ma jor pre-Laramide hydrothermal event was identified, which was comprise d of a west to east migration of warm, saline brines. This was followe d by a major circulation of meteoric water in the Rockies during Laram ide uplift. In the southern Omineca extensional zone, convecting surfa ce fluids penetrated to the brittle-ductile transition at 350-450 degr ees C and locally into the underlying more ductile rocks. A principal conclusion of the study is that most quartz +/- carbonate veins in met amorphic rocks in the southern Canadian Cordillera precipitated from d eeply convected surface fluids. This conclusion supports a surface flu id convection model for the genesis of mesothermal Au-quartz veins, co mmon in greenschist-facies rocks worldwide. The combination of our geo chemical results with the results of other Lithoprobe studies indicate s that widespread and deep convection of surface fluids in rocks under going active metamorphism is a commonplace phenomena in extensional se ttings, while in compressional-thrust settings the depth of penetratio n of surface fluids is more limited.