During the past decade, the study of paleomagnetism has provided compelling evidence for the displacement and accretion of Alaskan terranes. As indicated by paleomagnetic measurements of ancient latitudes, large areas of crust that now form part of Alaska were once located at lower latitudes with respect to the North American craton. Triassic volcanic rocks, for example, in the Wrangellia terrane of southern Alaska show a poleward shift in latitude greater than 27° (3,000 km). The large displacements that we infer from paleomagnetic data are consistent with the concept that most of Alaska is made up of displaced lithotectonic terranes, which Silberling and others (this volume) defined on the basis of paleontologic and stratigraphic differences. Paleomagnetic studies provide the basic data for measuring the rates of movement and for determining the arrival times of far-travelled terranes along the continental margin. Using this information, we can refine plate-tectonic models by comparing terrane movements with predicted relative motions between North America and the oceanic plates of the Pacific basin.
Paleomagnetic poles from the stable part of North America define a frame of reference for comparison with the paleolatitudes of Cordilleran terranes. This frame of reference, sometimes called the apparent polar wander (APW) path, has been compiled from numerous studies undertaken during the past three decades (McElhinny, 1973, p. 201-206; Irving, 1979; Irving and Irving, 1982). By 1970, the confirmation of sea-floor spreading and the refinement of cratonic reference poles strengthened the interpretation that paleomagnetic anomalies in the Cordillera were the result of translations
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The Geology of Alaska
You get a comprehensive overview of the geology, tectonic evolution, and mineral resources of Alaska and adjacent areas of the continental margin. Plates include state-wide maps showing geology, physiography, lithotectonic terranes, metamorphic rocks, igneous rocks, sedimentary basins, isotopic age data, neotectonics, isostatic gravity, magnetics, and metallic mineral deposits. Summaries of bedrock geology and geologic history are given for eleven large regions of Alaska and adjacent offshore areas. Twenty topical chapters synthesize data on metamorphic and igneous rocks; major onshore and offshore sedimentary basins; the paleomagnetics evidence for latitudinal displacements and rotations, glacial history and periglacial phenomena; and the occurrence, evolution, and potential of Alaska's vast resources of petroleum, coal, and metallic minerals. A summary chapter provides an overview and presents a possible model for Alaska's Phanerozoic evolution. The Geology of Alaska is the largest publication produced in the Decade of North American Geology program, a fitting tribute to this magnificent area.