Origin of the northern Chukchi Borderland: volcanic features in a rifted continental setting

The Chukchi Borderland is a submerged, complex, bathymetric high in the Arctic Ocean. It is interpreted to be a rifted continental block, part of a larger microcontinent (including Alaska) that was involved in the poorly understood Cretaceous opening of Canada Basin. The northern extent of continental material in the Chukchi Borderland is difficult to map because of its overlap with the High Arctic Large Igneous Province (HALIP) identified by characteristic magnetic anomalies. Between 2008 and 2016, 1700 km of modern multichannel seismic reflection data and 15 sonobuoy refraction profiles were collected between Chukchi Plateau and Nautilus/Canada Basins. The morphology of this region is rough, with water depths increasing from 700-800 m at the top of Chukchi Plateau to 3500 m in a series of ramps and uplifts before reaching 3800 m in Nautilus and Canada Basins. Sedimentary cover is thin, less than 1 km, with a complex stratigraphy of angular unconformities.

Seismic basement is an irregular, bright surface that includes reflections interpreted as uplifted, faulted blocks. Beneath the bright basement reflection are weaker, dipping, strongly layered, and sometimes discontinuous reflections that reveal faults, truncations, folds, and variable dips. While some of these deeper layered reflections may be reverberations, they may also represent basalt flows associated with the HALIP, which is consistent with basalt known from dredge samples. Sonobuoy data in this northern region often recorded S-wave refractions. These doubly converted waves (both downward and upward traveling converted waves) are modeled as converted at the basement interface where the strong velocity contrast facilitates P- to S-wave conversion. Modeled Poisson's ratios fall in two ranges: 0.24 - 0.25 and 0.3 - 0.31. The lower range is interpreted to be indicative of continental crust while the higher range is similar to ratios measured in hyaloclastites from the North Atlantic. Hyaloclastites produced by subaqueous volcanism are known in this northern region from dredges. The resulting picture is that the northern continuation of the Chukchi Borderland consists of continental crust that may have been overlain by volcanic (basaltic?) flows. It therefore represents a rifted margin overprinted by the HALIP.