Integrated Geophysical and Geologic Investigation of the Crustal Structure of Western Canada Basin, Chukchi Borderland and Mendeleev Ridge, Arctic Ocean

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Intellectual merit: 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 deepCanada Basin, Northwind Ridge, Chukchi Borderland, Chukchi Basin, and Mendeleev Ridge; collectingseismic reflection data to determine depositional history and locate potential drill sites; and taking pistoncores to define the sedimentary history of the region. Regional geologic studies, seismic reflectionprofiling from conventional geophysical vessels along the periphery of the Arctic Basin and fromicebreakers within the polar ice pack, aerogeophysics, and satellite altimetry data have led manyresearchers to support the idea that the Amerasia Basin of the Arctic Ocean opened about a pivot point nearthe Mackenzie Delta. Simple reconstruction of the Amerasia Basin is precluded, however, by the presenceof the Chukchi Borderland, an extensive cluster of submarine plateaus in the Amerasia Basin north of theChukchi shelf, and by Mendeleev Ridge. If both the Borderland and the Alpha/Mendeleev Ridge areconstructed 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 andOrdovician shallow-water marine carbonates from Northwind Ridge that are similar to the basement rocksfound beneath the Sverdrup basin of the Canadian Arctic Archipelago. If Chukchi Borderland consists ofcontinental crust, complicated tectonic scenarios must be devised to explain its presence. The crustalcharacter of the Borderland is therefore critical to understanding the origin and kinematics of the AmerasiaBasin's opening. Northwind Ridge, the easternmost plateau of the Chukchi Borderland, faces the EarlyCretaceous 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 AmerasiaBasin. Because Northwind Ridge is a high-standing plateau that adjoins the tectonically enigmaticNorthwind Escarpment, understanding the crustal character of the Chukchi Borderland and the contrastbetween it and that of the deep Canada Basin is very important. Virtually nothing is known of the crustalstructure and seismic stratigraphy of Mendeleev Ridge. They will conduct a seismic reflection andrefraction experiment to resolve fundamental questions concerning the tectonic evolution of the AmerasiaBasin. Cross tracks from the deeper Canada Basin across the Northwind Ridge should determine whetherit has operated as a transform margin, convergent margin or neither. Understanding the evolution of theCanada Basin and its development as a deep-water basin is fundamental to such basic concerns as sea levelfluctuations 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 canbe 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 requiredfor a fast interpretation of the crustal structure of the Chukchi Borderland and the Mendeleev Ridge. Thedata 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 todetermine 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 drillingoperations 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 ofthe Arctic. Determination of the crustal structure of both Chukchi Borderland and Mendeleev Ridge hasimportant 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.