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Harbert, W.P., 1987

Tectonics of Alaska, plate tectonics of the Pacific basin, and paleomagnetism of the Aleutian arc

Bibliographic Reference

Harbert, W.P., 1987, Tectonics of Alaska, plate tectonics of the Pacific basin, and paleomagnetism of the Aleutian arc: Palo Alto, California, Stanford University, Ph.D. dissertation, 327 p., illust., maps.


In this thesis several independent observations are used to describe the tectonics and structure of the Aleutian Islands, the Aleutian forearc and the Pacific plate boundary. Relative plate motion poles, reflection seismic profiles and paleomagnetic methods are used to describe the tectonics of Alaska and the plate tectonics of the Pacific basin. Periods of strong convergence between the continental Eurasian and North American plates in the arctic from Maastrichtian to Paleocene and transform motion between these plates from middle to upper Eocene are correlated with deformational and plutonic events in the Bering sea region. Combined geologic and seismic reflection data show that the Atka Basin appears to have formed in response to a combination of initiation of trench-floor-filling turbidite deposition, an increased rate and normal component in Pacific plate subduction and formation of a broad and thick accretionary wedge. Paleomagnetic inclinations from early Oligocene aged units in the Aleutian Islands are not significantly different from that expected for the North America plate during the early Oligocene. Tectonic rotation of paleomagnetic delinations are commonly observed along island arcs and the edges of continental plates. Using a rotational block model that assumes a pair of master strike-flip faults between which rotation occurs, paleomagnetic data from the Aleutian arc shows that the amount of required strike-slip motion along the crest of the arc is only a small fraction (no more than 4%) of total tangential North America-Pacific motion. To constrain the Neogene motion of the Pacific plate magnetic isochrons 2A, 3, 3A and 4 were modelled from marine magnetic traverses of the ridge. Our analysis suggests that a change in Pacific-Antarctic relative motion occurred between chron 2A and the beginning of chron 3 time. Calculation of Pacific-North America Euler poles suggests that this change in Pacific motion corresponded to a change from strike-slip to transpression in the Mendocino region of Northern California. We have investigated the position of the northern boundary of the Pacific Tertiary, rotation of blocks along the Aleutian arc, the development and deformation of the central Aleutian forearc, and a recent change in Pacific-hotspot, and Pacific-North America motion. These studies have shown the importance of plate tectonics and paleomagnetism to the accurate understanding of deformed regions.

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