Tectonostratigraphy of Mino terrane: Jurassic accretionary complex of southwest Japan
Abstract The Mino terrane, a disrupted accretionary terrane in central Japan, consists of four fault-bounded mappable units of Mesozoic and Paleozoic unmetamorphosed sedimentary rocks. The four units are described as (1) Permian greenstone-carbonate-chert unit, (2) Lower Triassic to lowest Cretaceous siliceous pelagite-distal turbidite unit, (3) Middle Jurassic proximal turbidite unit, and (4) upper Lower Jurassic to lowest Cretaceous olistostrome-slump unit. The first unit is interpreted as a sedimentary cover which was formed on and around a seamount in an open-ocean setting. The second unit records the accumulation of deep-water radiolarian-rich sediments in a pelagic realm and a tapering wedge of trench turbidites. The third unit contains submarine fan sediments deposited in a possible trench-slope basin. The forth unit, labeled as sedimentary melange containing blocks derived from accretionary prisms, is considered to be submarine deposits which accumulated in a lower trench-slope basin to trench floor setting. An originally southward-vergent imbricate stacking of structural wedges of these four units characterizes the highly complicated structure of the Mino terrane rocks. Collision and subsequent offscraping accretion of Permian to Middle Jurassic oceanic rocks and Lower Jurassic to lowest Cretaceous clastic rocks provide the most satisfactory explanation for juxtaposition of the structural wedges of the four units which were originally laid down in largely different depositional sites. These tectonic events most probably took place during Early Jurassic to Early Cretaceous time along an active continental margin of East Asia.