The Central Asian Orogenic Belt ( c . 1000–250 Ma) formed by accretion of island arcs, ophiolites, oceanic islands, seamounts, accretionary wedges, oceanic plateaux and microcontinents in a manner comparable with that of circum-Pacific Mesozoic–Cenozoic accretionary orogens. Palaeomagnetic and palaeofloral data indicate that early accretion (Vendian–Ordovician) took place when Baltica and Siberia were separated by a wide ocean. Island arcs and Precambrian microcontinents accreted to the active margins of the two continents or amalgamated in an oceanic setting (as in Kazakhstan) by roll-back and collision, forming a huge accretionary collage. The Palaeo-Asian Ocean closed in the Permian with formation of the Solonker suture. We evaluate contrasting tectonic models for the evolution of the orogenic belt. Current information provides little support for the main tenets of the one- or three-arc Kipchak model; current data suggest that an archipelago-type (Indonesian) model is more viable. Some diagnostic features of ridge–trench interaction are present in the Central Asian orogen (e.g. granites, adakites, boninites, near-trench magmatism, Alaskan-type mafic–ultramafic complexes, high-temperature metamorphic belts that prograde rapidly from low-grade belts, rhyolitic ash-fall tuffs). They offer a promising perspective for future investigations.

/pdf/tectonic-models-for-accretion-of-the-central-asian-orogenic-4rjcoan76s.pdf

Tectonic models for accretion of the Central Asian Orogenic Belt

[1] The Solonker suture records the termination of the central Asian Orogenic Belt (CAOB). However, tectonic development of the Solonker suture is poorly understood. We report new field data for the Ondor Sum melange in the Ulan valley, and present a new evaluation of the orogenic belt extending from the southern Mongolia cratonic boundary to the north China craton within the context of a new geological framework and tectonic model, which incorporates relevant data from the literature. The southern accretionary zone between the north China craton and the Solonker suture is characterized by the Mid-Ordovician-Early Silurian Ulan island arc-Ondor Sum subduction-accretion complex and the Bainaimiao arc. This zone was consolidated by the Carboniferous-Permian when it evolved into an Andean-type magmatic margin above a south dipping subduction zone. The northern accretionary zone north of the Solonker suture extends southward from a Devonian to Carboniferous active continental margin, through the Hegenshan ophiolite-arc accretionary complex to the Late Carboniferous Baolidao arc associated with some accreted Precambrian blocks. This northern zone had consolidated by the Permian when it developed into an Andean-type magmatic margin above a north dipping subduction zone. Final subduction of the central Asian ocean caused the two opposing active continental margins to collide, leading to formation of the Solonker suture in the end-Permian. Predominant northward subduction during final formation of the suture gave rise in the upper northern plate to a large-scale, postcollisional, south directed thrust and fold belt in the Triassic-Jurassic. In summary, the CAOB underwent three final stages of tectonic development: early Japanese-type accretion, Andean-type magmatism, and Himalayan-type collision.

/pdf/accretion-leading-to-collision-and-the-permian-solonker-3zbth9mq3w.pdf

Accretion leading to collision and the Permian Solonker suture, Inner Mongolia, China: Termination of the central Asian orogenic belt

http://sourcedb.igg.cas.cn/cn/zjrck/200907/W020101130538853730453.pdf

Middle Cambrian to Permian subduction-related accretionary orogenesis of Northern Xinjiang, NW China: Implications for the tectonic evolution of central Asia

The Altaids is one of the largest accretionary orogenic collages in the world with the highest rate of Phanerozoic continental growth and significant metallogenic importance. It is widely accepted that subduction-related orogenesis of the Altaids started in the late Precambrian and gradually migrated southward (present coordinates). However, it is uncertain when and how the building of the Altaids was finally completed. Based on structural geology, geochemical, geochronological, and paleomagnetic data, this paper presents late Paleozoic to early Mesozoic accretionary tectonics of two key areas, North Xinjiang in the west and Inner Mongolia in the east, together with neighboring Mongolia. The late Paleozoic tectonics of North Xinjiang and adjacent areas were characterized by continuous southward accretion along the wide southern active margin of Siberia and its final amalgamation with the passive margin of Tarim, which may have lasted to the end-Permian to early/mid-Triassic. In contrast, in Inner Mongolia and adjacent areas two wide accretionary wedges developed along the southern active margin of Siberia and the northern active margin of the North China craton, which may have lasted to the mid-Triassic. The final products of the long-lived accretionary processes in the southern Altaids include late Paleozoic to Permian arcs, late Paleozoic to mid-Triassic accretionary wedges composed of radiolarian cherts, pillow lavas, and ophiolitic fragments, and high-pressure/ultrahigh-pressure metamorphic rocks. Permian Alaskan-type zoned mafic-ultramafic complexes intruded along some major faults of the Tien Shan. We define a new Tarim suture zone immediately north of the Tarim craton that is probably now buried below the Tien Shan as a result of northward subduction of the Tarim block in the Cenozoic. The docking of the Tarim and North China cratons against the southern active margin of Siberia in the end-Permian to mid-Triassic resulted in the final closure of the Paleoasian Ocean and terminated the accretionary orogenesis of the southern Altaids in this part of Central Asia. This complex geodynamic evolution led to formation of giant metal deposits in Central Asia and to substantial continental growth.

/pdf/end-permian-to-mid-triassic-termination-of-the-accretionary-4halebz94r.pdf

End-Permian to mid-Triassic termination of the accretionary processes of the southern Altaids: implications for the geodynamic evolution, Phanerozoic continental growth, and metallogeny of Central Asia

Abstract Asia is the world’s largest composite continent, comprising numerous old cratonic blocks and young mobile belts. During the Phanerozoic it was enlarged by successive accretion of dispersed Gondwana-derived terranes. The opening and closing of palaeo-oceans would have inevitably produced a certain amount of fresh mantle-derived juvenile crust. The Central Asian Orogenic Belt (CAOB), otherwise known as the Altaid tectonic collage, is now celebrated for its accretionary tectonics and massive juvenile crustal production in the Phanerozoic. It is composed of a variety of tectonic units, including Precambrian microcontinental blocks, ancient island arcs, ocean island, accretionary complexes, ophiolites and passive continental margins. Yet, the most outstanding feature is the vast expanse of granitic intrusions and their volcanic equivalents. Since granitoids are generated in lower-to-middle crustal conditions, they are used to probe the nature of their crustal sources, and to evaluate the relative contribution of juvenile v. recycled crust in the orogenic belts. Using the Nd-Sr isotope tracer technique, the majority of granitoids from the CAOB can be shown to contain high proportions (60 to 100%) of the mantle component in their generation. This implies an important crustal growth in continental scale during the period of 500–100 Ma. The evolution of the CAOB undoubtedly involved both lateral and vertical accretion of juvenile material. The lateral accretion implies stacking of arc complexes, accompanied by amalgamation of old microcontinental blocks. Parts of the accreted arc assemblages were later converted into granitoids via underplating of basaltic magmas. The emplacement of large volumes of post-accretionary alkaline and peralkaline granites was most likely achieved by vertical accretion through a series of processes, including underplating of basaltic magma, mixing of basaltic liquid with lower-crustal rocks, partial melting of the mixed lithologies leading to generation of granitic liquids, and followed by fractional crystallization. The recognition of vast juvenile terranes in the Canadian Cordillera, the western US, the Appalachians and the Central Asian Orogenic Belt has considerably changed our view on the growth rate of the continental crust in the Phanerozoic.

The Central Asian orogenic belt and growth of the continental crust in the Phanerozoic

The paper reviews and integrates new results on the evolution of the Paleo-Asian Ocean and its related geodynamics and geology of Altai-Sayan Region (ASR) in Central Asia. A revised terrane classification based on Vendian-Cambrian geodynamic units and evolution of terranes is described. Reactivated suture zones along the terrane boundaries are proposed. The obtained data suggest the important role of strike-slip deformations in the formation of mosaic-block structure of Central Asia. Those complicated and multi-stage deformations resulted from the Late Devonian-Early Carboniferous collision of Gondwana-derived terranes. The deformations reached their peak in the Late Carboniferous-Permian due to the collision of the Kazakhstan and Siberian continents. A system of sinistral strike-slip faults formed ASR along the margin of the Siberian continent as a result of the Late Carboniferous-Permian collision. The intrusion of granites occurred in East Kazakhstan and northwestern Gorny Altai in the Late Carboniferous and Permian. This resulted in the formation of the Northern Eurasia continent. Geodynamic evolution of the Paleo-Asian ocean and paleotectonics of ASR allow to recognize in the region the following five geodynamic stages: Vendian-Early Cambrian, Early Ordovician, Early-Middle Devonian, Late-Devonian-Early Carboniferous and Late Carboniferous-Early Permian times.

https://www.igm.nsc.ru/labs/lab212/~safonova/pdf/gsj-busl2001.pdf

Evolution of the Paleo-Asian Ocean (Altai-Sayan Region, Central Asia) and collision of possible Gondwana-derived terranes with the southern marginal part of the Siberian continent

Late Paleozoic-Early Mesozoic Geodynamics of Central Asia

Equipment for Studying the Earth’s Magnetic Field

AbstractUpper Cretaceous magnetostratigraphy of northern West Siberia has been reconstructed using new paleomagnetic data from five wells in the Kharampur oil-gas-condensate field (1049, 109N, 106P-Yu, 105N, and 2073N). The scientific motivation of this investigation was to construct a composite Upper Cretaceous magnetostratigraphic section of the north of Western Siberia based on integrated paleomagnetic and biostratigraphic data, which represent a part of the Upper Cretaceous magnetic polarity scale of all Western Siberia. The study area is located within the Middle Pur trench in the Pur-Taz interfluve. Natural remanent magnetization in the samples of the Pokur, Dorozhkovo, Okhteurievka, Kuznetsovo, Lower Berezovo, and Upper Berezovo Formations was analyzed by stepwise alternated field (AF) and thermal demagnetization and used to compile the magnetostratigraphic sections of the five wells. Correlations among the well sections form a basis for a composite magnetostratigraphic record of Upper Cretaceous (Cenomanian through Campanian) strata in the area. The composite section comprises two normal polarity zones NK2(sn-st) and NK2cp and correlates with the regional Upper Cretaceous magnetostratigraphic section of southern West Siberia, as well as with the global polarity time scale.KeywordsPaleomagnetismMagnetostratigraphyGeomagnetic polarityMagnetozoneUpper CretaceousPur-Taz interfluveNorthern West Siberia 

N. N. Semakov

Papers

Evolution of the Paleo-Asian Ocean (Altai-Sayan Region, Central Asia) and collision of possible Gondwana-derived terranes with the southern marginal part of the Siberian continent

Late Paleozoic-Early Mesozoic Geodynamics of Central Asia

Equipment for Studying the Earth’s Magnetic Field

Upper Cretaceous Paleomagnetism and Magnetostratigraphy of the Pur-Taz Interfluve (Northern West Siberia)