Revisiting the “Klondike Orogeny”: Permian to Jurassic Development of the Yukon-Tanana Terrane, Northern Canadian Cordillera

Abstract

The Permian evolution of the Yukon-Tanana terrane and closure of the Slide Mountain Ocean in the northern Cordillera have been inferred to culminate in the collisional “Klondike orogeny,” a northern extension of the Sonoma orogeny of the western USA. The “Klondike orogeny” was thought to be associated with mid-crustal deformation and metamorphism and development of a thick orogenic welt in the late Permian (ca. 260–252 Ma; Lopingian). A review of lithogeochemical data combined with new U-Pb geochronology and Hf isotope data of igneous and detrital zircons from the western Yukon-Tanana terrane supports development of a mid to late Permian (ca. 265–255 Ma; Guadalupian-Lopingian) arc in a supra-subduction zone setting. Arc development was preceded by hyper-extension and emplacement of supra-subduction zone ophiolites (ca. 268–264 Ma). Precise CA-TIMS U-Pb dating of zircon in plutons inferred to constrain the timing of the “Klondike orogeny” show that they are the same age (ca. 260.9 Ma) and that previous dates are too young due to unmitigated Pb loss. A critical review of evidence for regional metamorphism indicates that mid-crustal deformation and metamorphism is related to accretion of the Intermontane terranes in the Early Jurassic. Mica cooling ages show that the western Yukon-Tanana terrane was exhumed to upper crustal level in the Jurassic. Sinistral transpression facilitated development of the Yukon-Tanana terrane and subsequent tectonic activity from mid-Paleozoic to early Mesozoic and probably linked the Permian closure of the Slide Mountain Ocean with intermittent late Paleozoic deformation culminating in the Sonoma orogeny of the U.S. Cordillera.