EXTENDED INNINGS: MID-CRETACEOUS (STARTING AT ~110 MA) OROGENESIS IN THE INTERMONTANE TERRANE AFTER THE INSULAR TERRANE HITS THE NORTHERN-NORTH AMERICAN WESTERN MARGIN

The Northern North American Cordillera consists primarily of two distinct composite terranes: the Intermontane and Insular (or Wrangellia composite) terranes. The timing of accretion of the Intermontane terrane with the former North America continental margin is well constrained to have been completed by the middle Jurassic. The timing of the accretion of the Insular terrane with the docked Intermontane terrane is, however, disputed with estimates as old as middle Jurassic to as young as Late Cretaceous. This study uses a compilation of published British Columbia, Yukon, Alaska bedrock geochronology ages (N=1664 from the Insular terrane, N=744 from the Intermontane terrane) to further investigate the accretionary history of the Insular terrane between 160 Ma to 80 Ma. This time period incorporates the terminal accretion of Intermontane terrane and closure of marine basins that separated the Insular and Intermontane terranes. We also perform a palinspastic reconstruction of the Insular terrane along the Denali fault, aligning Insular-Intermontane dissected Jura-Cretaceous basins. North of 60°N there is a dominant ~110 Ma deformation signal in the Intermontane terrane which we attribute to well-documented mid-Cretaceous extension in east-central Alaska-Yukon and to escape tectonics after the initial docking of the Insular terrane at ~117 Ma. In contrast, there is no distinct mid to Late Cretaceous cooling signal along this segment of the Insular terrane. We suggest that the cooling signal of mid-Cretaceous collision recorded within the Insular terrane in Alaska and the Yukon is diminished by latest Cretaceous-Paleogene arc magmatism and Cenozoic plate boundary events (i.e. Yakutat flat- slab subduction). South of 60°N there are no dominant cooling signals during the Cretaceous period on either the Intermontane or the Insular terrane. This muted cooling record may be related to syn-arc magmatism masking the arrival of the Insular terrane, docking of a thinner segment of the Insular terrane, presence of a stronger segment of the Intermontane terrane, and/or the presence of a wider segment of the Intermontane leading to more distributed deformation. Overall, we demonstrate the terminal accretion of the Insular terrane and the closure of the Northern Cordillera Jura-Cretaceous marine basin progressed in a more complex manner than previously recognized.