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

Geochronology of the Phanerozoic granitoids in northeastern China

A synopsis of events related to the assembly of eastern Gondwana

Paleozoic multiple accretionary and collisional tectonics of the Chinese Tianshan orogenic collage

A review of the western part of the Altaids: A key to understanding the architecture of accretionary orogens

Isotope provinces, mechanisms of generation and sources of the continental crust in the Central Asian mobile belt: geological and isotopic evidence

/pdf/early-stages-of-the-paleoasian-ocean-formation-results-of-3dmf05yrt7.pdf

Early stages of the Paleoasian Ocean formation: Results of geochronological, isotopic, and geochemical investigations of Late Riphean and Vendian-Cambrian complexes in the Central Asian Foldbelt

U-Pb age of Syn- and postmetamorphic granitoids of south Mongolia : Evidence for the presence of grenvillides in the central Asian foldbelt

The succession of magmatic events associated with development of the Early Carboniferous-Early Permian marginal continental magmatic belt of southern Mongolia is studied. In the belt structure there are defined the successive rock complexes: the older one represented by differentiated basalt-andesite-rhyodacite series and younger bimodal complex of basalt-comendite-trachyrhyolite composition. The granodiorite-plagiogranite and banatite (diorite-monzonite-granodiorite) plutonic massifs are associated with the former, while peralkaline granite massifs are characteristic of the latter. First systematic geochronological study of igneous rock associations is performed to establish time succession and structural position of both complexes. Geochronological results and geological relations between rocks of the bimodal and differentiated complexes showed first that rocks of the differentiated complex originated 350 to 330 Ma ago at the initial stage of development of the marginal continental belt. This is evident from geochronological dates obtained for the Adzh-Bogd and Edrengiyn-Nuruu massifs and for volcanic associations of the complex. The dates are consistent with paleontological data. The bimodal association was formed later, 320 to 290 Ma ago. The time span separating formation of two igneous complexes ranges from several to 20–30 m.y. in different areas of the marginal belt. The bimodal magmatism was interrelated with rifting responsible for development of the Gobi-Tien Shan rift zone in the belt axial part and the Main Mongolian lineament along the belt northern boundary. Loci of bimodal rift magmatism likely migrated with time: the respective magmatic activity first initiated on the west of the rift system and then advanced gradually eastward with development of rift structures. Normal granitoids untypical but occurring nevertheless among the products of rift magmatism in addition to peralkaline massifs are assumed to have been formed, when the basic magmatism associated with rifting stimulated crustal anatexis and generation of crustal granitoid magmas under specific conditions of rifting within the active continental margin.

Geochronology of igneous rocks and formation of the Late Paleozoic south Mongolian active margin of the Siberian continent

New data on the geology and tectonics of the main structural elements of the East Transbaikalian segment of the Central Asian Foldbelt are discussed. Correlation charts of the main stratified and igneous complexes are compiled. The rocks of the Baikal-Patom and Baikal-Muya belts, as well as the Barguzin-Vitim Superterrane, are characterized by new Nd isotopic data, which have allowed us to establish the sources of these rocks, to separate isotopic provinces, and to distinguish two stages of crust-forming processes: the Early Baikalian (1.0–0.8 Ga) and the Late Baikalian (0.70–0.62 Ga). The Early Baikalian crust was formed in relatively narrow and spatially isolated troughs of the Baikal-Muya Belt and probably in the Amalat Terrane, whereas the Late Baikalian continental crust was formed and reworked in the Karalon-Mamakan, Yana, and Katera-Uakit zones of the Baikal-Muya Belt. The Baikal-Patom Belt and most of the Anamakit-Muya Zone in the Baikal-Muya Belt are characterized by remobilization of the Early Precambrian continental crust and by a subordinate role of Late Riphean juvenile sources. Reworking of the mixed Late Riphean and Early Precambrian crustal sources is typical of the Barguzin-Vitim Superterrane. The origination and evolution of the continental crust in the studied region are considered in light of new data; alternative versions of paleogedynamic reconstructions are discussed.

V. P. Kovach

Papers

Isotope provinces, mechanisms of generation and sources of the continental crust in the Central Asian mobile belt: geological and isotopic evidence

Early stages of the Paleoasian Ocean formation: Results of geochronological, isotopic, and geochemical investigations of Late Riphean and Vendian-Cambrian complexes in the Central Asian Foldbelt

U-Pb age of Syn- and postmetamorphic granitoids of south Mongolia : Evidence for the presence of grenvillides in the central Asian foldbelt

Geochronology of igneous rocks and formation of the Late Paleozoic south Mongolian active margin of the Siberian continent

Isotopic structure and evolution of the continental crust in the East Transbaikalian segment of the Central Asian Foldbelt