NEW INSIGHTS ON ARCTIC CRUSTAL STRUCTURE AND TECTONIC FRAMEWORK FROM CANADIAN - U.S. JOINT ICEBREAKER OPERATIONS IN THE AMERASIA BASIN

Canada and the United States conducted joint icebreaker operations in the Amerasia Basin from 2007 to 2011 to acquire over 15000 km of seismic reflection and bathymetry data. Over 170 expendable sonobuoys were deployed to collect p-wave refraction and wide angle reflection data. Dredge samples were collected from northern Chukchi Plateu and Nautilus Spur. These new data, combined with circum-Arctic bathymetry, gravity and magnetic compilations, greatly enhance onshore/offshore mapping of crustal domains and structural elements, in particular the Canadian and Alaskan margins, the deep Canada Basin, the Alpha Ridge, and Makarov Basin.

The two-icebreaker operations resulted in the high quality seismic reflection data. The short-offset (16 channel) data imaged the base of the sedimentary succession and structures within the upper crust. Basement morphology is highly varied and complex. Large grabens, basement ridges and seamounts are observed as well as broadly distributed volcanoclastics and localized volcanic flows and sill intrusions.

The sonobuoy results define the regional velocity structure of the sedimentary succession and were used to depth-convert the seismic reflection data. The velocity models also provide constraints on the composition of the sediments, and the crustal velocities allow quantitative mapping of continental, oceanic, and transitional domains.

2-D gravity and magnetic models have been generated along several of the seismic lines using the sonobuoy velocities to constrain density parameters. Laboratory measurements of the new grab samples show the velocity-density relationships are consistent with standard published curves. These models provide useful visualization of rift styles along the margins, and estimates of crustal thickness. Integrated with detailed interpretation of magnetic anomalies, the models allow for revised calculation of the direction and magnitude of overall extension for opening of the Canada Basin.

We highlight these and other results from the on-going Canadian/U.S. cooperation on Arctic geological and tectonic studies. We will present a summary of these results with recently published material into a new “tectonic events” chart to continue the discussion on the timing and evolution of the Amerasia Basin.