Terrane analysis and accretion in North‐East Asia

Abstract

Abstract A terrane map of North‐East Asia at 1:5 000 000 scale has been compiled. The map shows terranes of different types and ages accreted to the North‐Asian craton in the Mesozoic–Cenozoic, sub‐and superterranes, together with post‐amalgamation and post‐accretion assemblages.The great Kolyma‐Omolon superterrane adjoins the north‐east craton margin. It is composed of large angular terranes of continental affinity: craton fragments and fragments of the passive continental margin of Siberia, and island arc, oceanic and turbidite terranes that are unconformably overlain by shallow marine Middle‐Upper Jurassic deposits. The superterrane resulted from a long subduction of the Paleo‐Pacific oceanic crust beneath the Alazeya arc. Its south‐west boundary is defined by the Late Jurassic Uyandina‐Yasachnaya marginal volcanic arc which was brought about by subduction of the oceanic crust that separated the superterrane from Siberia. According to paleomagnetic evidence the width of the basin is estimated to be 1500–2000 km. Accretion of the superterrane to Siberia is dated to the late Late Jurassic‐Neocomian. The north‐east superterrane boundary is defined by the Lyakhov‐South Anyui suture which extends across southern Chukotka up to Alaska. Collision of the superterrane with the Chukotka shelf terrane is dated to the middle of the Cretaceous.The Okhotsk‐Chukotka belt, composed of Albian‐Late Cretaceous undeformed continental volcan‐ites, defines the Cretaceous margin of North Asia. Terranes eastward of the belt are mainly of oceanic affinity: island arc upon oceanic crust, accretion wedge and turbidite terranes, as well as cratonic terranes and fragments of magmatic arcs on the continental crust and metamorphic terranes of unclear origin and age. The time of their accretion is constrained by post‐accretionary volcanic belts that extend parallel to the Okhotsk‐Chukotka belt but are displaced to the east: the Maastrichtian‐Miocene Kamchatka‐Koryak belt and the Eocene‐Quaternary Central Kamchatka belt which mark active margins of the continent of corresponding ages.