摘要:

AbstractNewly obtained radiolarian biostratigraphic age combined with previous isotopic age of the Troodos ophiolite shows that the ophiolite becomes systematically younger from east to west: Turonian, early Campanian, and late Campanian. The youngest late Campanian part of the ophiolite is directly covered by the volcaniclastic sediment derived from an active island arc, whereas the older part is covered by pelagic radiolarite. These facts constitute evidence that the Troodos ophiolite was probably emplaced during the subduction of an active spreading ridge.

ISSN:1038-4871    

DOI:10.1111/j.1440-1738.1993.tb00070.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe significance of timing and formation of mélange in accretionary prisms, particularly concerning basaltic and related rocks and pelagic sediments, is exemplified in the Sawadani area of the Jurassic Chichibu accretionary complex in Shikoku, southwest Japan. Major and trace element geochemistry of the basaltic and related rocks indicates that all are of a hot‐spot origin which produced a seamount. Most of the rocks have a trend of differentiation from an alkalic parental magma. The time relationship between the blocks and matrices of the mélange deduced from radiolarian fossil evidence and macro‐ to microscopic characteristics of contacts between different lithologies indicates two stages of mixing of materials in the seafloor. The first mixing occurred on the flank of the seamount in the pelagic environments in the Late Permian, and the second occurred on the trench floor or in the accretionary prism after the Early Jurassic. These two stages show respectively the geological phenomena of a seamount within the Izanagi‐Kula plate and its incorporation into the Asian continental

ISSN:1038-4871    

DOI:10.1111/j.1440-1738.1993.tb00071.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe history of Mesozoic accretion and growth of the Asia eastern margin, occupied by Southeastern Russia, includes five main events; two main tectonic regimes were responsible for the growth of the continent. In the Triassic‐Jurassic, Early Cretaceous and Late Cretaceous‐Paleogene, the subduction of the oceanic lithosphere resulted in the formation of wide accretionary wedges of the Mongol‐Okhotsk, Khingan‐Okhotsk and Eastern Sikhote‐Alin active continental margins, respectively. These stages of the comparatively slow growth of the continent were broken by stages of rapid growth and drastic changes in the shape of the continent, since at these stages large terranes of various tectonic nature collided with active continental margins. At the end of the Early‐Middle Jurassic, the Bureya terranes collided with the Mongol‐Okhotsk active margin, and at the beginning of the Late Cretaceous there was collision of the Central and Southern Sikhote‐Alin terranes with the Khingan‐Okhotsk active margin.Collision‐related structural styles in all cases are indicative of oblique collision and great strike‐slip motions along the main sutures. The peculiarities of the terrane's geological structure show that prior to collision with the Mongol‐Okhotsk and Khingan‐Okhotsk active margins, they had already accreted to Asia and then migrated along its margins along the strike‐slip faults. The Bureya terranes were squeezed out of the compression zone between Siberia and North China. This compression zone originated after the Paleozoic oceans which divided these cratons had closed. The Khanka terranes and Mesozoic accretionary wedge terranes of the Sikhote‐Alin shifted along the strike‐slip faults subparallel to the Asia Pacific margin. Strike‐slip motions resulted in duplication

ISSN:1038-4871    

DOI:10.1111/j.1440-1738.1993.tb00072.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA 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

ISSN:1038-4871    

DOI:10.1111/j.1440-1738.1993.tb00073.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY