Principal Investigators: Lawrence Lawver and Harm Van Avendonk

Funding agency: National Science Foundation (Award# ARC-0327626)

Abstract: The Principal Investigators will undertake an integrated geophysical and geological study of the western section of the Amerasian Basin of the Arctic Ocean to include: determining the crustal structure of the deep Canada Basin, Northwind Ridge, Chukchi Borderland, Chukchi Basin, and Mendeleev Ridge; collecting seismic reflection data to determine depositional history and locate potential drill sites; and taking piston cores to define the sedimentary history of the region. Regional geologic studies, seismic reflection profiling from conventional geophysical vessels along the periphery of the Arctic Basin and from icebreakers within the polar ice pack, aerogeophysics, and satellite altimetry data have led many researchers to support the idea that the Amerasia Basin of the Arctic Ocean opened about a pivot point near the Mackenzie Delta. Simple reconstruction of the Amerasia Basin is precluded, however, by the presence of the Chukchi Borderland, an extensive cluster of submarine plateaus in the Amerasia Basin north of the Chukchi shelf, and by Mendeleev Ridge. If both the Borderland and the Alpha/Mendeleev Ridge are constructed of igneous rocks that postdate opening of the Amerasia Basin, simple closure is not a problem. However, Grantz and others have cored Phanerozoic sediments, including Cambrian and Ordovician shallow-water marine carbonates from Northwind Ridge that are similar to the basement rocks found beneath the Sverdrup basin of the Canadian Arctic Archipelago. If Chukchi Borderland consists of continental crust, complicated tectonic scenarios must be devised to explain its presence. The crustal character of the Borderland is therefore critical to understanding the origin and kinematics of the Amerasia Basin's opening. Northwind Ridge, the easternmost plateau of the Chukchi Borderland, faces the Early Cretaceous Canada Basin (the largest and deepest part of the Amerasia Basin) at Northwind Escarpment. The escarpment is a distinctive feature invoked in many tectonic models for the opening of the Amerasia Basin. Because Northwind Ridge is a high-standing plateau that adjoins the tectonically enigmatic Northwind Escarpment, understanding the crustal character of the Chukchi Borderland and the contrast between it and that of the deep Canada Basin is very important. Virtually nothing is known of the crustal structure and seismic stratigraphy of Mendeleev Ridge. They will conduct a seismic reflection and refraction experiment to resolve fundamental questions concerning the tectonic evolution of the Amerasia Basin. Cross tracks from the deeper Canada Basin across the Northwind Ridge should determine whether it has operated as a transform margin, convergent margin or neither. Understanding the evolution of the Canada Basin and its development as a deep-water basin is fundamental to such basic concerns as sea level fluctuations and paleoclimate in the Mesozoic.

The experiment will require building 25 sea-ice seismometers [SIS] that will be deployed on the ice using the U.S. Coast Guard (USCG) helicopters. The hydrophone of the SIS will be deployed through a hole augered through the ice. Radio transmitters will allow monitoring of the arrival data on board so that the SISs can be retrieved as soon as the refracted arrivals are observed. A global positioning system (GPS) unit in the SIS will provide continuous location. A basic arrival time versus offset analysis of real-time data will provide key information required for a fast interpretation of the crustal structure of the Chukchi Borderland and the Mendeleev Ridge. The data will also be used in iterative travel-time tomographic inversions to delineate details of the velocity structure. The velocity structure will be used in conjunction with existing seismic reflection and geologic data to produce complete crustal sections of Chukchi Borderland, Chukchi Basin and Mendeleev Ridge. The resulting crustal sections will be used to calibrate existing ship, satellite, submarine and aerogravity data, to construct realistic models, and to address such questions as the tectonic origin and degree of extension in the Chukchi Borderland, the origin of Mendeleev Ridge, and to determine whether there has been convergence between Northwind Ridge and Canada Basin. Broader Impacts: The Principal Investigators will include at least four crossed lines suitable for siting future drilling operations in the region. The IODP drill sites will be used to study the climate history of the Arctic region, ocean circulation patterns, and impact of ice-covered versus ice-free conditions on the biotic evolution of the Arctic. Determination of the crustal structure of both Chukchi Borderland and Mendeleev Ridge has important implications for Law of the Sea considerations. Three graduate students and a minimum number of two undergraduates will be recruited to participate in this cruise.