Luke Beranek and colleagues from the University of Iowa, Geological Survey of Canada, Yukon Geological Survey, and University of Minnesota-Duluth have published a new article in Tectonics.
Cordilleran-type batholiths record the non-steady state development of continental arcs, including short periods (~5-20 m.y.) of high-volume magmatic addition that punctuate longer periods (~30-50 m.y.) of low-level background activity. In the orogen cyclicity model of DeCelles et al. (2009), short-lived “flare-up” events occur in response to the rapid underthrusting of melt-fertile lower crust and lithospheric mantle beneath a continental arc as a result of craton-directed retroarc deformation. High-volume magmatic additions thicken the crust and generate large residual roots that may subsequently founder beneath continental arcs. Jurassic to Eocene intrusive rocks of the Coast Mountains batholith in western Canada represent one of the great continental arc systems of the world and have significant potential to identify the orogenic linkages proposed by DeCelles et al. (2009). In this paper, a Late Jurassic flare-up event in the Coast Mountains arc system of SW Yukon is reported using a combination of SIMS zircon U-Pb geochronology, zircon REE geochemistry, and whole-rock lithogeochemistry. Estimated intrusive rates in the Coast Mountains batholith were ~350 km2/m.y., analogous in scale to the Late Jurassic flare-up of the Sierra Nevada arc system. 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 lull in most of the Coast Mountains batholith, which may be linked to ridge subduction, lithospheric delamination, mantle cooling, or plate reorganization.