Ophiolites in accretionary complexes along the Early Cretaceous margin of NE Asia: age, composition, and geodynamic diversity

Abstract

AbstractThe existing published data, combined with our own new field, petrographic, and geochemical observations and data show that ophiolites of the West Koryak fold system originated in a variety of tectonic environments. This fold system stretches along the boundary shared by two of NE Asia’s largest tectonic units, the Verkhoyansk-Chukotka and Koryak-Kamchatka foldbelts. The fold system abounds in Palaeozoic and Mesozoic ophiolites and sedimentary and volcanic island-arc assemblages. The ophiolites are Palaeozoic and Mesozoic in age. The variety of geological and geochemical signatures implies ophiolite origin in diverse tectonic settings. The Early Palaeozoic ophiolites of the Ganychalan accreted terrane and Devonian(?) ophiolites of the Ust-Belaya accreted terrane are fragments of the Panthalassan oceanic lithosphere. Serpentinite mélange in the Ust-Belaya terrane contains some blocks of island-arc provenance. They are probably Late Palaeozoic-Early Mesozoic in age as determined by K-Ar measurements, which require validation by other techniques. Mesozoic, chiefly Late Jurassic-Early Cretaceous ophiolites of the Beregovoi and Kuyul accreted terranes, originated in a suprasubduction-zone (SSZ) setting (ensimatic island arc and back-arc basin). Among the Mesozoic ophiolites, one finds blocks of oceanic assemblages in serpentinite mélanges as well. Basalt and chert blocks of clearly oceanic derivation are viewed as detached fragments of the upper part of the oceanic lithosphere. The ophiolites have experienced a variety of accretionary scenarios. Palaeozoic ophiolites docked onto the Koni-Taigonos island arc (of Late Palaeozoic-Early Mesozoic age), probably in the Late Palaeozoic or Early Mesozoic, whereas Mesozoic ophiolites accreted onto the Uda-Murgal island arc (of Late Jurassic-Early Cretaceous age) in the terminal Early Cretaceous. Sedimentary deposits, whose base is late Albian in age, make a post-accretionary sequence. These island arcs portray the overall history of the convergent boundary between the North Asian continent and NW Pacific. Ophiolites of the Ganychalan and Ust-Belaya terranes consist of thrust sheets and, jointly with Yelistratov Peninsula ophiolites, make up the basement to the forearc of the Uda-Murgal island arc, ophiolites of Cape Povorotny and Kuyul terrane being incorporated in accretionary prisms of the same arc. Ophiolites and associated metamorphic, volcanic, and sedimentary rocks of Palaeozoic-Early Cretaceous age underwent three deformation phases, each reflecting a different stage in the evolution of the NE Asian continental margin and readily correlative with principal tectonic events in the northern Circum-Pacific region.