The northern Canadian Cordillera exhibits coeval accreted arc, subduction zone, ocean basin, and continental margin assemblages that make the region an exceptional place to understand tectonic processes involved in arc‐continent collision. In this study, we use U‐Pb zircon and monazite geochronology to define the timing and provenance record of Late Permian collisional orogeny related to the accretion of the Yukon‐Tanana terrane onto the ancestral North American continental margin of northwestern Canada. New U‐Pb crystallization ages of Permian intrusive rocks in the Klondike District of western Yukon bracket the timing of collision‐related ductile deformation and greenschist‐ to amphibolite‐facies metamorphism on the Yukon‐Tanana terrane between 260 and 252.5 Ma. This tectonothermal event is herein named the Klondike orogeny. Detrital zircon U‐Pb geochronology of Triassic strata provides the sedimentary record of arc‐continent collision and crustal reworking along the Cordilleran margin. Arc‐derived detrital zircons in Early to Middle Triassic (251–235 Ma) strata overlying the ancestral North American continental margin in Yukon suggest that a foreland‐style basin developed adjacent to the Klondike orogen. Regionally extensive Late Triassic (235–200 Ma) strata containing primarily North American detrital zircons form an overlap assemblage that covered the accreted terranes and western North America. The timing of the Klondike orogeny is roughly synchronous with other contractional events along the ∼5000 km strike length of the Cordillera, including the Late Permian‐Early Triassic Sonoman orogeny in Nevada. Global plate reorganization linked to assembly of Pangaea may have been the tectonic engine for late Paleozoic‐early Mesozoic development of the North American Cordillera.

The Whitehorse trough is an Early to Middle Jurassic marine sedimentary basin that overlaps the Intermontane terranes in the northern Cordillera. Detrital zircon dates from eight Laberge Group sandstones from various parts of the trough all display a major Late Triassic-Early Jurassic peak (220-180 Ma) and a minor peak in the mid-Paleozoic (340-330 Ma), corresponding exactly with known igneous ages from areas surrounding the trough. Source regions generally have Early Jurassic (ca. 200-180 Ma) mica cooling dates, and the petrology of metamorphic rocks and Early Jurassic granitoid plutons flanking the trough suggests rapid exhumation during emplacement. These data suggest that subsidence and coarse clastic sedimentation in the trough occurred concurrently with rapid exhumation of the shoulders. Isolated occurrences of sandstone and conglomerate units with similar detrital zircon signatures occur west and east of the trough, as well as overlapping the Cache Creek terrane, indicating that either the trough was once more extensive, or isolated basins tapped similar sources. Development of these sedimentary basins and accompanying rapid exhumation in the northern Cordillera were coeval with the onset of orogenic activity in the hinterland of the southern Canadian Cordillera, and subsidence in the western Canada foreland sedimentary basin. The Whitehorse trough is interpreted as a forearc basin that progressively evolved into a collisional, synorogenic piggyback basin developed atop the nascent Cordilleran orogen. Upper Jurassic-Lower Cretaceous fluvial deposits overlapping the Whitehorse trough have detrital zircons that were mainly derived from recycling of the Laberge Group, but they also contain zircons exotic to the northern Intermontane terranes that are interpreted to reflect windblown detritus from the Late Jurassic-Early Cretaceous magmatic arc that developed either atop the approaching Insular terranes to the west or southern Stikinia.

Various plate reconstructions predict that the Alexander terrane, a Neoproterozoic-Jurassic crustal fragment now located in the North American Cordillera, evolved in proximity to the northern Appalachian-Caledonian convergent margin during assembly of supercontinent Laurussia. To test stratigraphic connections with Laurussia that are implied by these plate reconstructions, we measured the Hf isotopic compositions of 176 detrital zircons from two relevant sedimentary sequences of the Alexander terrane. An older, Upper Silurian-Lower Devonian terrestrial to shallow-marine molasse sequence yields 405-490 Ma detrital zircons with negative ε Hf(t) values and Mesoproterozoic to Paleoproterozoic Hf model ages. In combination with paleomagnetic and biogeographic constraints, these Hf data argue for the molasse strata to be now-displaced equivalents of the Old Red Sandstone and primarily sourced from crustally contaminated granitoids in the Greenland, Svalbard, or British Caledonides. Late Silurian-Early Devonian orogenesis in the Alexander terrane is therefore likely related to the Scandian-Salinic phase of Appalachian-Caledonian mountain building. Younger, Middle Devonian sequences of the Alexander terrane are endowed in 390-490 Ma detrital zircons with positive ε Hf(t) values and Neoproterozoic Hf model ages. These isotopic signatures are consistent with the erosion of local basement rocks during the opening of the Slide Mountain-Angayucham backarc rift and tectonic separation of the Alexander terrane from northern Laurussia.

Two large tectonic terranes, Alexander and Wrangellia, at the northwestern margin of North America, have long been considered exotic to each other and the rest of the northern Cordillera. Pennsylvanian plutons tie the two terranes together, but their seemingly dissimilar geological character led most workers to believe the two evolved separately before and after the Pennsylvanian. New chemical abrasion zircon U-Pb geochronology, whole-rock geochemistry, and other geological evidence from Paleozoic magmatic rocks in Yukon, Canada, suggest that the terranes evolved together by the late Paleozoic and that the Alexander terrane partially forms the basement to a portion of Wrangellia. Large ca. 363 Ma gabbro complexes have non-arc geochemical signatures and intrude both terranes. Volcanic rocks near the base of northern Wrangellia are ca. 352 Ma and have back-arc to N-MORB geochemical signatures. At higher stratigraphic levels, Wrangellia contains abundant Mississippian to Pennsylvanian arc volcanic and volcaniclastic rocks (Skolai arc). Similar-aged arc/back-arc rocks are found in the southern part of Wrangellia (Sicker arc) and are interpreted as the southern extension of the Skolai arc. We propose that the gabbros represent the initiation of extension through an arc located at the margin of the Alexander terrane (Skolai/ Sicker arc system). Extension progressed enough to deposit basalts within a back-arc basin setting. Subduction reversal closed the basin and rejuvenated the arc in the Pennsylvanian. Collision of the arc with the Alexander terrane led to exhumation and deposition of conglomerates unconformably on top of the gabbros. The evolution of the Alexander terrane and Wrangellia proposed here is broadly similar to the Late Devonian plate tectonic history along the northwestern Laurentian margin and is likely part of the same chain of arcs/back-arcs.