Abstract

The basin-forming process along a convergent margin off the eastern coast of Eurasia was pursued on the basis of geological, geochemical, and geophysical approaches. Central Hokkaido has been a site of vigorous tectonic events throughout the Cenozoic reflecting the long-standing subduction of oceanic plates in the region. Geochemical modeling provided an estimate of the eroded Paleogene unit in the study area. Data on the considerable thickness of the missing unit implied continued subsidence of the forearc region and its subsequent exhumation under the emergence of a compressive regime synchronous with the back-arc opening stage. Spatially large facies variety in the Paleogene system suggests that basin compartmentalization occurred as a result of the trench-parallel component of the plate convergence. Right-lateral motion seems to have been the dominant type in Hokkaido and the forearc of northeast Japan since the Late Cretaceous, except for a left-lateral episode during rapid subsidence of the Izanagi Plate around 110 Ma. Numerical modeling demonstrated that dextral slip on a bunch of longitudinal strike-slip faults restored the Neogenedepocenters in central Hokkaido, together with an east-west compressive regime related to an arc-arc collision.