Foreland Basins at the Miocene Arc-Arc Junction, Central Hokkaido, Northern Japan

Abstract

During the Miocene age, a series of foreland basins were formed in Hokkaido, the northern island of Japan, due to an arc-arc collision event [2–4]. The basin area has a total length of 400 km, and it is characterized by several rows of deep depressions stretched in a north-south direction and separated by topographic highs (Figure 1). The degree of total crustal shortening and exhumation by the collision event is larger in the southern region of the collision zone [5], and thus, the basin geometry and the stratigraphic/sedimentologic architecture of the basin fills vary among the depressions. Namely, the depression in the southern region has suffered progressive deformation due to thrust propagation, and the depocenter has migrated forelandward, a feature noted in many foreland basins [1]. In contrast, the depression in the northern region shows restrictive deformation and foreland-ward migration of depocenter. Thus, the initial geometry and stratigraphic architecture of the basin fill are well preserved even in the proximal margin of the basin. On the other hand, unlike the northern and southern regions, the depression located near the center of the foreland basin area has been affected by the existence of a projection on the foreland lithosphere. As a result, the depression shows very narrow basin geometry and restrictive foreland-ward migration of the depocenter.