ONLAND ACCRETIONARY WEDGE IN THE MIURA AND BOSO PENINSULAS, CENTRAL JAPAN: ONE OF THE BEST ANALOGS OF MODERN SUBDUCTION-ACCRETION SYSTEM

Since there are major missing links between studies of modern accretionary complex (most examples are composed of late Miocene and younger sediments which are recovered from 1-2 km depths) and ancient accretionary complex (most examples are older than Eocene, experienced max. burial depth deeper than 5 km), the progressive variation of deformation, physical/chemical properties, and diagenetic/metamorphic processes along the subduction mega-thrust has not been successively traced. The Miura and Boso area, central Japan is a unique example representing a young and shallowly buried ancient accretionary wedge that gives us great opportunity to study the missing links and to perform complementary studies of modern accretionary wedges with its spatial and time variations.

The Miura and Boso are composed of two accretionary complexes: the early to middle Miocene Hota accretionary complex buried only 2-4 km, and the late Miocene to early Pliocene Miura-Boso accretionary complex buried less than 1 km with overlying several trench-slope basin sediments. They uplifted rapidly due to the Izu-Bonin island arc collision and therefore have never experienced deeper burial, thermal, and physical overprinting. These accretionary complexes preserve successive variation of deformation and related physical/chemical properties from soon after sedimentation to just prior to seismogenic realm.

In this presentation, we will show the geologic framework of accretionary wedge in the Miura and Boso areas, corresponding characteristics on physical properties and deformation/fabrics, and comparison with modern-plate convergent margins such as Nankai (SW Japan) and Kanto (central Japan) regions.