The paper provides a review of the published and new geological and geochronological data on the metamorphic rocks in the Kurai accretionary prism, considering the evolution of the Kuznetsk-Altai island-arc paleosubduction channel of the Siberian continent. The following two stages are distinguished by 40Ar/39Ar and U/Pb dating: (1) 636–619 Ma and earlier: sinking of ophiolites into the subduction zone; (2) 604–585 Ma: sinking of the large bo­dies of oceanic uplifts into the subduction zone. These processes led to the exhumation of the high-pressure rocks and the hot Chagan-Uzun peridotites. The dynamo-thermal effect of the latter on the basalts is reflected in the inverted metamorphic zoning and the occurrence of garnet amphibolites and plagiogranite migmatites. It is probable that the paleo-seamounts collided with the island arc during the Vendian–Early Cambrian. The data reviewed in this paper give evidence of an active margin of the West Pacific type in the western Altai-Sayan folded region in the Vendian–Cambrian.

Middle-Late Paleozoic geodynamics and structure of Gorny Altai are studied with reference to gravity data. The northern and central parts of the area belong to the Gorny Altai terrane consisting of Late Precambrian-Paleozoic rocks originated in different tectonic settings on the Siberian continental margin, including Devonian active-margin volcanoplutonic complexes. In the south and east, the Gorny Altai terrane borders the Altai-Mongolia terrane along the Charysh-Terekta-Ulagan shear zone. The Altai-Mongolia terrane is composed of Early Paleozoic turbidites of the Kazakhstan-Baikal continent, Middle Paleozoic collisional garnet-disthene-andalusite schists, and Late Paleozoic zoned andalusite-cordierite schists, with granitic plutons on their periphery. The pattern of these complexes is similar to that of Cenozoic volcanoplutonic and metamorphic domes in the Kamchatka and Chukchi Peninsulas. The Devonian volcanoplutonic complexes from the Gorny Altai terrane and the Middle-Late Paleozoic metamorphic complexes from the Altai-Mongolia terrane are well evident in the gravity field. In general, gravity anomalies in the two terranes strike in different directions: NW in the Gorny Altai terrane and W-E in the Altai-Mongolia terrane, which highlights the structural heterogeneity of the Gorny Altai region. New dates have been obtained for magmatic detrital zircons from Paleozoic sedimentary rocks of the Anui-Chuya basin in the Gorny Altai terrane. The inferred source areas of zircon hosts are igneous rocks of the Precambrian craton basement and the Vendian-Early Ordovician Kuznetsk-Altai island arc. Early Neoproterozoic (1.00-0.75 Ma) detrital zircons are abundant in the Early Paleozoic turbidites of the Altai-Mongolia terrane but are absent from samples of the Gorny Altai terrane. Populations of detrital zircons in the the Gorny Altai terrane contain Devonian and Early Neoproterozoic specimens. The reported data prove that the Kazakhstan-Baikal and Siberian continents amalgamated in the Middle-Late Paleozoic. The resulting Gorny Altai tectonic framework of that time is recorded in the gravity field and in the provenance of detrital zircons. (C) 2017, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

The Central Asian Orogenic Belt is a gigantic tectonic collage of numerous accreted terranes. However, its geodynamic evolution has been hotly debated primarily due to incomplete knowledge on the nature of these enigmatic terranes. This work presents new detrital zircon U–Pb and Hf isotopic data to constrain the crustal nature and origin of the Russian Altai, a critical segment of Altai-Mongolian terrane. The youngest zircon 206Pb/238U ages of 470Ma constrain that the Terekta Formation, previously envisaged as Precambrian basement, was actually deposited after the Middle Ordovician. As for the three more sedimentary sequences above the Terekta Formation, they have youngest zircon 206Pb/238U ages of 425Ma, 440Ma and 380Ma, respectively, indicating their depositions likely in the Late Silurian to Devonian. From all analyses, it is noted that many zircon U–Pb ages cluster at ca. 520Ma and ca. 800Ma, and these zircons display oscillatory zoning and have subhedral to euhedral morphology, which, collectively, suggests that adjacent Neoproterozoic to Paleozoic igneous rocks were possibly dominant in the sedimentary provenance. Additionally, a few rounded Archean to Mesoproterozoic zircon grains are characterized by complex texture, which are interpreted as recycling materials probably derived from the Tuva–Mongolian microcontinent. Precambrian rocks have not been identified in the Russian Altai, Chinese Altai and Mongolian Altai so far, therefore, Precambrian basement may not exist in the Altai-Mongolian terrane, but this terrane probably represents a large subduction–accretion complex built on the margin of the Tuva–Mongolian microcontinent in the Early Paleozoic. Multiple episodes of ridge–trench interaction may have caused inputs of mantle-derived magmas to trigger partial melting of the newly accreted crustal materials, which contributed to the accretionary complex. During accretionary orogenesis of the CAOB, formation of such subduction–accretion complex is likely ubiquitous, indicating continental crust growth by both lateral accumulation and vertical basaltic injection.

M.M. Buslov a,c,*, H. Geng b, A.V. Travin a, D. Otgonbaatar c,d, A.V. Kulikova a,c, Chen Ming b, G. Stijn e, N.N. Semakov a,c, E.S. Rubanova a,c, M.A. Abildaeva a,c, E.E. Voitishek c, D.A. Trofimova a,c a V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia b Department of Earth Sciences, University of Hong Kong, Pokfulam Road, Hong Kong c Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia d Institute of Geology and Mineral Resources, Mongolian Academy of Sciences, Peace Ave. 63, P.O. Box 118, Ulaanbaatar, 210351, Mongolia e Ghent University, Sint-Pietersneuwstraat 25, B-9000, Ghent, Belgium

Packages of Late Paleozoic tectonic nappes and associated major NE-trending strike-slip faults are widely developed in the Altai-Sayan folded area. Fragments of early deformational phases are preserved within the Late Paleozoic allochthons and autochthons. Caledonian fold-nappe and strike-slip structures, as well as accompanying metamorphism and granitization in the region, are typical of the EW-trending suture-shear zone separating the composite Kazakhstan-Baikal continent and Siberia. In the Gorny Altai region, the Late Paleozoic nappes envelop the autochthon, which contains a fragment of the Vendian-Cambrian Kuznetsk-Altai island arc with accretionary wedges of the Biya-Katun' and Kurai zones. The fold-nappe deformations within the latter zones occurred during the Late Cambrian (Salairian) and can thus be considered Salairian orogenic phases. The Salairian fold-nappe structure is stratigraphically overlain by a thick (up to 15 km) well-stratified rock unit of the Anyui-Chuya zone, which is composed of Middle Cambrian-Early Ordovician fore-arc basin rocks unconformably overlain by Ordovician-Early Devonian carbonate-terrigenous passive-margin sequences. These rocks are crosscut by intrusions and overlain by a vokanosedimentary unit of the Devonian active margin. The top of the section is marked by Famennian-Visean molasse deposits onlapping onto Devonian rocks. The molasse deposits accumulated above a major unconformity reflects a major Late Paleozoic phase of folding, which is most pronounced in deformations at the edges of the autochthon, nearby the Kaim, Charysh-Terekta, and Teletskoe-Kurai fault nappe zones. Upper Carboniferous coal-bearing molasse deposits are preserved as tectonic wedges within the Charysh-Terekta and Teletskoe-Kurai fault nappe zones.Detrital zircon ages from Middle Cambrian-Early Ordovician rocks of the Anyui-Chuya fore-arc zone indicate that they were primarily derived from Upper Neoproterozoic-Cambrian igneous rocks of the Kuznetsk-Altai island arc or, to a lesser extent, from an Ordovician-Early Devonian passive margin. A minor age population is represented by Paleoproterozoic grains, which was probably sourced from the Siberian craton. Zircons from the Late Carboniferous molasse deposits have much wider age spectra, ranging from Middle Devonian-Early Carboniferous to Late Ordovician-Early Silurian, Cambrian-Early Ordovician, Mesoproterozoic, Early-Middle Proterozoic, and early Paleoproterozoic. These ages are consistent with the ages of igneous and metamorphic rocks of the composite Kazakhstan-Baikal continent, which includes the Tuva-Mongolian island arc with accreted Gondwanan blocks, and a Caledonian suture-shear zone in the north. Our results suggest that the Altai-Sayan region is represented by a complex aggregate of units of different geodynamic affinity. On the one hand, these are continental margin rocks of western Siberia, containing only remnants of oceanic crust embedded in accretionary structures. On the other hand, they are represented by the Kazakhstan-Baikal continent composed of fragments of Gondwanan continental blocks. In the Early-Middle Paleozoic, they were separated by the Ob'-Zaisan oceanic basin, whose fragments are preserved in the Caledonian suture-shear zone. The movements during the Late Paleozoic occurred along older, reactivated structures and produced the large intracontinental Central Asian orogen, which is interpreted to be a far-field effect of the colliding East European, Siberian, and Kazakhstan-Baikal continents. (C) 2013, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.