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Phanerozoic tectonic evolution of the Circum-North Pacific

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. ABSTRACT The Phanerozoic tectonic evolution of the Circum-North Pacific is recorded mainly in the erogenic collages of the Circum-North Pacific mountain belts that separate the North Pacific from the eastern North Asian and western North American Cratons. The collages consist of tectonostratigraphic terranes, composed of fragments of igneous arcs, accretionary-wedge and subduction-zone complexes, passive continental margins, and cratons, that are overlapped by continental margin arc and sedimentary basin assemblages. The geologic history of terranes and overlap assemblages is highly complicated because of post-accretion dismemberment and translation during strike-slip faulting that occurred subparallel to continental margins. The complex tectonics of this region is analyzed by the following steps. (1) Tectonic environments for the erogenic collage are assigned from regional compilation and synthesis of stratigraphic and faunal data. The tectonic environments include cratonal, passive continental margin, metamorphosed continental margin, continental-margin arc, island arc; oceanic crust, seamount, and ophiolite, accretionary wedge and subduction zone, turbidite basin, and metamorphic. (2) Correlations are made between terranes. (3) Coeval terranes are grouped into a single tectonic origin, i.e., a single island arc or subduction zone. (4) Igneous arc and subduction zone terranes, that are interpreted as being tectonically linked, are grouped into coeval, curvilinear arc-subduction zone complexes. (5) By use of geologic, faunal, and paleomagnetic data, the original positions of terranes are interpreted. And (6) the paths of tectonic migration are constructed. Six processes overlapping in time were responsible for most of the complexities of the collage of terranes and overlap assemblages around the Circum-North Pacific. First, in the Late Proterozoic, and the Late Devonian and Early Carboniferous, major periods of rifting occurred along the margins of Northeast Asia and northwestern part of the North American Cordillera. The rifting resulted in fragmentation and formation of cratonal and passive continental margin terranes from each continent that eventually migrated and accreted to other sites along the evolving margins of the original or adjacent continents. Second, from about the Late Triassic through the mid-Cretaceous, a succession of island arcs and tectonically paired subduction zones formed near continental margins. Third, from about mainly the mid-Cretaceous through the Present, a succession of igneous arcs and …