GENETIC LINKS AMONG FLUID CYCLING, VEIN FORMATION, REGIONAL DEFORMATION, AND PLUTONISM IN THE JUNEAU GOLD BELT, SOUTHEASTERN ALASKA

Gold-bearing quartz vein systems in the Juneau gold belt formed within a 160-km-long by 5- to 8-km-wide zone along the western margin of the Coast Mountains, Alaska. Vein systems are spatially associated with s hear zones adjacent to terrane-bounding, mid-Cretaceous thrust faults. Analysis of vein orientations and sense of shear data define a stress configuration with greatest and least principal axes oriented subhori zontally with northeast-southwest trends and subvertically, respective ly. This local stress configuration is compatible with the far-field p late configuration during Eocene time. Isotopic ages of vein formation indicate that fluid cycling occurred between 56.5 and greater-than-or -equal-to 52.8 Ma, and are consistent with a genetic link between vein ing and a change in plate motion in early Eocene time. Veining was als o synchronous with the latter stages of rapid exhumation and voluminou s plutonism immediately inboard of the gold belt. We propose a model i n which interacting tectonic events facilitated fault-valve action and vein development along now-exhumed shear zones.