Late Jurassic flare‐up of the Coast Mountains arc system, NW Canada, and dynamic linkages across the northern Cordilleran orogen

Short-lived, high-volume magmatic events or flare-ups in Cordilleran-style accretionary systems are presumably triggered by the rapid underthrusting of melt-fertile lithosphere beneath a continental arc during extreme retroarc shortening. New zircon U-Pb age and trace element geochemical studies of the Coast Mountains batholith were conducted to test this hypothesis and investigate cross-orogen linkages between the Coast Mountains arc system and adjacent retroarc elements of the Canadian Cordillera. Late Jurassic (155-147Ma) granitoids of the Saint Elias plutonic suite in southwestern Yukon were emplaced during a widespread magmatic event and correspond to an intrusive rate of similar to 350km(2)/Myr, analogous to the scale of 160-150Ma flare-up activity in the Sierra Nevada batholith. The timing of Late Jurassic high-volume magmatism was coincident with forearc and intraarc deformation events along the length of the Coast Mountains arc from Alaska to British Columbia. Whole-rock and zircon rare earth element geochemical results from the Saint Elias plutonic suite confirm that continental lithosphere was a key source component for Late Jurassic granitoids, which strengthens the implied relationship between high-volume arc magmatism and crustal recycling. Well-documented episodes of late Middle to early Late Jurassic hinterland thrusting and metamorphism in the Intermontane and Omineca belts of the Canadian Cordillera preceded this high-volume event and therefore support the hypothesis that retroarc shortening was dynamically linked to flare-up activity. Late Jurassic magmatism was followed by a 140-125Ma lull in most of the Coast Mountains batholith, which may be linked to ridge subduction, lithospheric delamination, mantle cooling, or plate reorganization.