Late Triassic to Jurassic Magmatic and Tectonic Evolution of the Intermontane Terranes in Yukon, Northern Canadian Cordillera: Transition From Arc to Syn‐Collisional Magmatism and Post‐Collisional Lithospheric Delamination

Abstract

Crustal growth at convergent margins is generally thought to occur through accretion of juvenile arc crust and/ or addition of magmatic material to the edge of a craton (e.g., Rudnick, 1995). Arc-continent collision zones are thus major sites for crustal growth through time (e.g., Brown et al., 2011). Arc accretion generally leads to development of an accretionary orogen, associated magmatism and basin(s) (e.g., Cawood et al., 2009;Draut & Clift, 2012). The evolution of arc-continent collision zones is generally complex and shows a wide-range of variations depending on configuration of continental and arc crusts, and angle and rates of convergence (Brown et al., 2011). There is no simple model that explains the variations observed in modern and ancient arc-continent collisions.In western North America, the development of the northern Cordilleran accretionary orogen began with collision of early Mesozoic peri-Laurentian arcs with the continental margin in latest Triassic to

Supplemental Material: Development of the Whitehorse trough as a strike-slip basin during Early to Middle Jurassic arc-continent collision in the Canadian Cordillera

“…The laser-ablation split-stream technique, which allows for the simultaneous collection of U-Pb and Hf isotope data in zircon (e.g., Fisher et al, 2014;Beranek et al, 2020), was used to identify juvenile to evolved source rocks and characterize an isotopic pull-down recorded by Laberge Group strata. This isotopic pattern matches the one recognized in syncollisional plutonic rocks that intruded the Intermontane terranes during an Early Jurassic episode of crustal thickening in the northern Canadian Cordillera (Colpron et al, 2022). We combined our new detrital zircon U-Pb-Hf isotope data with published fossil and U-Pb results (Colpron, 2011;Colpron et al, 2015;Bordet et al, 2019) to constrain Sinemurian to Toarcian maximum depositional ages for Laberge Group units and basin-filling patterns.…”

“…Laberge Group deposition was coeval with the onset of Jurassic foreland basin subsidence in Alberta (Fernie Formation in Fig. 1; Cant and Stockmal, 1989;Price, 1994;Pana et al, 2018) and suggests that the development of the Whitehorse trough accompanied the rise of the Cordilleran hinterland-retroarc thrust system (Colpron et al, 2015(Colpron et al, , 2022.…”

“…The Late Triassic to Middle Jurassic (all stratigraphic and numerical ages follow the time scale of Cohen et al, 2013) tectonic evolution of the northern Canadian Cordillera was marked by waning arc magmatism, arc collision, syn-to postcollisional magmatism, and syntectonic filling of the Whitehorse trough, which overlaps Upper Triassic and older rocks of the Stikinia and Cache Creek terranes from central Yukon to northern British Columbia (Figs. 1 and 2; e.g., Mihalynuk et al, 1994;English and Johnston, 2005;Colpron et al, 2015Colpron et al, , 2022. Late Triassic to Middle Jurassic arc collision was accommodated by the enclosure of the Cache Creek terrane and resulted in crustal thickening and burial of Yukon-Tanana terrane rocks to 5-9 kbar (~16-30 km) in Yukon (e.g., Berman et al, 2007;Clark, 2017;Gaidies et al, 2021).…”

“…Late Triassic to Middle Jurassic arc collision was accommodated by the enclosure of the Cache Creek terrane and resulted in crustal thickening and burial of Yukon-Tanana terrane rocks to 5-9 kbar (~16-30 km) in Yukon (e.g., Berman et al, 2007;Clark, 2017;Gaidies et al, 2021). Late Triassic to Early Jurassic syncollisional plutons were emplaced at mid-to lower-crustal levels (5-7 kbar, ~16-23 km) into metamorphic basement along the flanks of the Whitehorse trough and subsequently cooled and exhumed at rates of 0.7-7.5 mm/yr (e.g., Johnston and Erdmer, 1995;Johnston et al, 1996;Knight et al, 2013;Colpron et al, 2022). Exhumation processes in central Yukon drove Early to Middle Jurassic erosion and resulted in the syntectonic deposition of the Laberge Group, a >3000-m-thick succession of immature marginal-marine to deep-marine strata that are typically interpreted to have filled a forearc basin (e.g., Dickie and Hein, 1995;English and Johnston, 2005) or a syncollisional basin that overlapped the northern Intermontane terranes (Colpron et al, 2015).…”

“…Exhumation processes in central Yukon drove Early to Middle Jurassic erosion and resulted in the syntectonic deposition of the Laberge Group, a >3000-m-thick succession of immature marginal-marine to deep-marine strata that are typically interpreted to have filled a forearc basin (e.g., Dickie and Hein, 1995;English and Johnston, 2005) or a syncollisional basin that overlapped the northern Intermontane terranes (Colpron et al, 2015). Recently, Colpron et al (2022) proposed that latest Triassic to Early Jurassic end-on arc collision in the northern Intermontane terranes was followed by southward migration of the Stikinia arc (Hazelton Group; Nelson et al, 2022) and that the collision zone in the north was linked to the retreating subduction zone by a sinistral transform fault system, possibly including the Llewellyn and Teslin faults (Currie and Parrish, 1993;Mihalynuk et al, 1999;de Keijzer et al, 2000). This new model predicts that sinistral transtension accommodated extensional exhumation of the orogen and subsidence of the Whitehorse trough as a strike-slip basin.…”