Evolution of clastic piles in an arc-arc collision zone: late cenozoic depositional history around the Tanzawa Mountains, central Honshu, Japan

Abstract

Late Cenozoic clastic piles around the Tanzawa Mountains represent trough (trench) landward and seaward basin-fills developed in an arc-arc collision zone in central Honshu, Japan. The landward basin-fills are clastic wedges prograded from the northern orogenic highlands and are characterized by fan deltaic successions succeeding submarine volcano-submarine fan/slope successions on basin plain deposits. The landward basin-fills were generally developed intermittently from north to south since the Middle Miocene. Evolution of the landward basin-fills depended on the interplay of the northward buoyant subduction and suturing of the Izu-Bonin arc in central Honshu (Honshu arc), together with submarine magmatism on the landward basin-slope emplaced by the subducting Pacific plate beneath the Izu-Bonin arc to the west. The seaward basin-fills, however, generally lack terrigenous detritus derived from the northern highlands, except for a trough fill which received some detritus shed from the rising highs just to the north, and are characterized by pyroclastic flow deposits prograded from the southern submarine volcanoes or a volcanic island on the ocean basin. The northward progradation of the pyroclastic flow deposits may have been emplaced by the northward drifting of the ocean basin. The Tanzawa Mountains, on the other hand, consist mainly of Early to Middle Miocene subaqueous volcaniclastic rocks intercalated with some volcanic conglomerates and shallow marine coquinas and can be interpreted as a Miocene volcanic island. Punctuated initiation and propagation of the Late Cenozoic basin-fills diachronously from the north to the south of the Tanzawa Mountains can be explained by northward drifting and collision of the Tanzawa Block (a paleo-volcanic island) with central Honshu, during Middle to Late Miocene and the consequent jump of the subduction zone to the south of it since Late Miocene, preceding the collision of the Izu Peninsula (Izu Block) with the south of the youngest basin-fills developed in the southern front of the Tanzawa Mountains since the Middle Pleistocene. After collision of the Izu Block with the southernmost basin-fills, the Late Cenozoic clastics in and around the Tanzawa Mountains were uplifted and deformed into northward imbricated structures by rapid slip on the faults framing this area.