TIMING AND GEOMETRY OF THE MULTI-STAGE BREAKUP OF RODINIA IN THE YUKON

We integrate new, precise U-Pb ID-TIMS ages on volcanic tuffs, rhyolite flows, and diabase dikes in the Coal Creek inlier (Ogilvie Mountains, western Yukon) with stratigraphic and structural relationships to construct a new model for the tectonic evolution of NW Laurentia. Preliminary investigations on the norhtern margin of the inlier reveal NW-trending, syn-sedimentary normal faults sealed by strata of the Fifteenmile Group that include an 811 Ma tuff. A NW facing shelf-slope break developed above the normal faults within the Fifteenmile Group with prograding stromatolite reefs stepping out into a shale-filled basin. Thus, by 811 Ma, a rifted-passive margin had developed on the NW margin of Laurentia. The margin was reactivated by 780 Ma with the Gunbarrel magmatic event, the development of a major unconformity under the Callison Lake Dolostone, west-vergent thrust faulting (Corn Creek orogeny), and extensive evaporite deposition in the Gypsum Formation, Little Dal Group. The nature of these events remains enigmatic. An ~1km-thick andesite-rhyolite edifice that developed along a north-down fault scarp by 717.4 Ma point to an additional Neoproterozoic extension event at ca. 720 Ma. The southern edge of Neoproterozoic carbonate strata in the Coal Creek inlier is the Cretaceous, north-vergent Dawson Thrust. We interpret this structure as a reactivated normal fault that approximates the edge of the south-facing late Neoproterozoic rifted margin of the Yukon. This model is consistent with the absence of strata equivalent to the Fifteenmile Group south of the Dawson fault and the correlation of the ‘grits’ of the Hyland Group with Windermere-age strata to the north. With these data, we propose a three-stage break-up of Rodinia on the NW margin of Laurentia. At ca. 850 Ma a NW-facing rifted margin developed, ca. 780 Ma marks an additional enigmatic tectonic event that included Gunbarrel magmatism, and at ca. 720 an additional south-facing rifted margin formed. These extensional episodes were further manifested in multiple phases of mafic intrusions between 850 and 700 Ma. The intrusions may have resulted from the presence of a large plume beneath the Ogilvie Arch, which functioned to buoy the paleo-peninsula, creating a paleo-high through much of the Cryogenian to early Paleozoic.