TECTONIC EVOLUTION OF THE ALTAIDS: CONCEPTS, CONTROVERSIES AND NEW IDEAS

The Altaids extends from the Urals to the Pacific and from the Siberian and East European (Baltica) cratons to the North China (Sino-Korean) and Tarim cratons. It began its tectonic history with oceanic subduction and growth at ca. 542 Ma and continued to ca. 250Ma, when the Palaeo-Asian Ocean (PAO) and its branches closed and the South Tianshan-Solonker suture was formed. However, the huge orogenic collage of Asia is either named the Central Asian Orogenic Belt (CAOB) or the Altaids, which are differnet in time and space. The Altaids formed from c. 542 Ma to 250 Ma and does not include the late Precambrian Baikalide – Pre-Uralide orogens, whereas the CAOB includes both and extends from ca. 1.0 Ga to 250 Ma.

The foundamental evolution of the Altaids/CAOB is controversial. Most scientists consider that CAOB formed by growth and accretion of many island arcs, oceanic islands, seamounts, accretionary wedges and microcontinents, but some believe that the Altaids comprises only one main island arc (the c. 7000 km long Kipchak – Tuva – Mongol arc) that formed inboard of the Baikalides and Pre-Uralides orogens. Later, successive roll-back of the arc in the Cambrian to mid-Silurian gave rise to the Khanty-Mansi back-arc ocean. Differential rotation of Siberia and Baltica led to duplication of the arc by strike-slip shuffling and to oroclinal bending and closure of the ocean by the late/end Palaeozoic. Several early Precambrian blocks within the orogen were rifted off the margins of Siberia and Baltica, but none from Gondwana.

In recent years much progress has been made in understanding the development of accretionary orogens including: (1) The tectonic attribution of microcontinents, (2) The time scales and tectonic settings of ophiolitic mélanges, (3) The nature and role of oceanic versus continental arcs, (4) The formation and dynamics of accretionary complexes, (5) The role of ultra-high pressure metamorphism, (6) The occurrence of ridge subduction, (7) Interactions between mantle plumes and plates. Many of these advances are relevant to the evolution of the Altaids and CAOB such as: (1) The early evolution and subduction initiation of the PAO, (2) The accretionary history of the extroversion of the PAO, (3) The nature of the mantle of the PAO, (4) The interactions between the PAO and the Paleo-Tethys Ocean, (5) The different styles of continental growth and excision, (6) The mechanism of formation of several major oroclines.