Mid-Ocean Ridge Subduction Offshore Alaska During the Cretaceous

We present a framework for the tectonic development of the Arctic region through a set of regional plate and ocean floor reconstructions since the early Cretaceous. In order to understand the effect of time-dependent geometries of mid-ocean ridges, subduction zones and collisional plate boundaries on Arctic basin evolution and reactivation through time, we reconstruct now subducted ocean floor, including portions of tectonic plates which have now entirely vanished, and restore their plate boundary configurations and subduction history. We reconstruct paleo-oceans by creating "synthetic plates", the locations and geometry of which are established on the basis of magnetic lineations and fracture zones, geological data and the rules of plate tectonics. The absolute position of the Pacific Plate and its surrounding plates is restored using a Pacific hotspot reference frame, whereas all other plates are reconstructed based on an African-Indian hotspot reference system. This approach is required because the Pacific Plate was entirely surrounded by subduction zones in the Cretaceous, and therefore Pacific Ocean plates cannot be related to other tectonic plates via relative plate motions. Our reconstructions reveal that the Izanagi-Farallon spreading ridge was subducted underneath Alaska from about 120-100Ma. Prior to 120 Ma the northern portion of the Izagani-Farallon plate boundary was a convergent boundary according to our reconstructions, implying that between 140 and 120 Ma a subducting slab was overridden by the Alaskan North Slope and possibly other associated terranes. The Izanagi-Farallon subduction zone (before 120 Ma) and mid-ocean ridge (after 120 Ma) was oriented roughly orthogonal to the overriding plate. Trench subduction would have been associated with negative dynamic topography on the overriding plate, whereas an eastward migrating slab window underneath North Slope and its border terranes may have resulted in asthenospheric upwelling and extension. Mid-Cretaceous (Aptian to Santonian) rocks are missing over much of the Alaska Peninsula, presumably eroded, and the widespread absence of rocks of this age suggests uplift and erosion of the entire terrane during a portion of Aptian to Santonian time. These observations generally support our model, but the relative roles of trench and ridge subduction for causing the widespread regional erosion or for triggering the opening of the Canada basin remain open.