The Altaids of Central Asia: A tectonic and evolutionary innovative review

The Altaids, one of the largest and long-lived accretionary orogens in the world, developed from ca. 600 Ma to 250 Ma by the multiple accretions of terranes of different origin, chiefly microcontinents and island arcs. Considerable geological information supported by geochemical, radiometric and isotopic data suggest that modern geodynamic processes such as seamounts/plateau accretion, ridge-trench interaction, the formation of supra-subduction ridges and back-arc basins, arc-arc collisions and oroclinal bending were responsible for the evolution of the Altaid archipelagos. Because of the paucity of palaeomagnetic and radiogenic data it is still not possible to present a definitive palaeo-reconstruction of the Altaids. Nevertheless, considering the voluminous literature appearing today on the Altaids, it is timely and appropriate to present a review of current understanding of the many inherent tectonic problems, some of which are controversial. The Altaids began its development in Vendian (610-570 Ma)-Early Palaeozoic oceans between three approaching cratons, Siberia, Gondwana and Tarim-North China, where it continually evolved during the Middle-Late Palaeozoic. The peri-Siberian part of the orogen formed around the microcontinents of Tuva-Mongolia and Altai-Mongolia through the multiple accretion of exotic Izu-Bonin-type island arcs (e.g. Uimen-Lebed, Lake-Khamsara), and oceanic islands/seamounts/plateaus (e.g. Kurai, Dzhida, Bayanhongor), and by the formation of back-arc basins (i.e. Altai-Sayan, Barguzin). These multiple accretion-collision events led to the formation of major peri-Siberian sutures by the end of the Early Palaeozoic (e.g. Bayanhongor, Dariv-Agardagh, Borus, Kurtushiba, Dzhida, Olkhon). The Mongol-Okhotsk Ocean opened within this new accreted continent in the Early-Middle Palaeozoic. The Kazakhstan Continent formed mostly by the Early Silurian in Eastern Gondwana by the accretion-collision of several ribbon-microcontinents (e.g. Chatkal-Karatau, Chu-Yili, Aktau-Junggar) and island arc-type terranes (e.g. Boshchekul-Chingiz, Baidaulet-Akbastau). Most Kazakhstan microcontinents originated in Gondwana from which they were detached through two probable stages of stretching in the Vendian and Amgaian (Middle Cambrian). Kazakhstan was finally created by formation of the Kumdykol, Kyrgyz-Terskey, Dzhalair-Naiman sutures in the Arenigian (Lower Ordovician), and by formation of the Maikain-Kyzyltas, Yili-Erementau sutures in the Hirnantian-Rhuddanian (Lower Silurian). The completed Kazakhstanian Continent moved westward toward Siberia and Tarim-North China in the Middle-Late Palaeozoic. The Tarim-North China craton(s) was likely located to the north of Eastern Gondwana during the Vendian-Early Palaeozoic. The tectonic evolution of the northern margin of Tarim-North China in the Early-Middle Palaeozoic mostly took place by island arc accretion (i.e. Tulinkai island arc), active margin accretion (i.e. Bainaimiao arc and Ondor Sum wedge) and by the opening of back-arc basins, which led to separation of the Central Tianshan-Hanshan Microcontinent. From the mid-Palaeozoic, Siberia, Tarim-North China and Kazakhstania began to mutually interact. The new plate tectonic arrangements led to the oroclinal bending and large-scale rotation of Kazakhstania during the Carboniferous, and to the main terminal sutures of the Altaids (i.e. South Tianshan, Turkestan, Uralian, Chara, Junggar-Balkash and Solonker) by the Permo-Triassic. Following the completion of the Altaids, only the Mongol-Okhotsk remained opened until the Jurassic-Cretaceous. During our synthesis we discuss alternative plate tectonic hypotheses, and we propose new models, which may provide potential perspectives for future investigations.