International Geologiical Congress - Oslo 2008

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ASI-06 Pre-Mesozoic accretionary tectonics in Central Asia

 

Plate tectonic reconstructions of the Central Asian Orogenic Belt

 

Caroline Wilhem, University of Lausanne (Switzerland)
Cyril Hochard, University of Lausanne (Switzerland)
Gérard M. Stampfli, University of Lausanne (Switzerland)
 

 

The large accretionary collage forming the Central Asian Orogenic Belt (CAOB) is located between the Siberian Craton to the North and the Tarim/North China Blocks to the South. The Urals Belt and the Pacific accretionary margin mark its western and eastern limit, respectively. During the last decade, geological knowledge about this orogenic belt increased considerably. Different global paleogeographic or regional tectonic models were discussed, and we propose here a first Paleozoic plate tectonic model of the CAOB replaced in a larger context.
The plate tectonic reconstruction method is based on paleomagnetism, paleogeographic data, geological data of geodynamic interest, plate kinematics and spatiotemporal constraints. In spite of the global dimension of our models, we work at the terrane scale, and a given area takes its true meaning only in a global context, as neighbouring areas create spatial constraints. At first, a terranes map, compiled from many publications, was established (ArcGIS software) and, subsequently, relevant geological data were added. The multitude of terranes and, thus, the multitude of sutures that form the Central Asian Orogenic Belt lead to a complex model.
The reconstructions start at 600Ma, at the time of the Panotia supercontinent. Siberia was isolated from other major blocks forming Panotia and the North China/Tarim blocks started to detach from the Cadomian plate nearly accreted to the northern margin of Gondwana. At that time, detachment, through roll-back forces, of a part of the Kazakhstan terranes (e.g. Chatkal-Karatau, Tourgai...) from the western margin of Siberia, and of some Mongolian terranes (e.g. Tuva-Mongolia, Khangai, Ereendavaa?) from the southern margin, took place. Some other microcontinents of the CAOB could have a North China/Tarim origin. Many terranes appeared only during the Paleozoic (e.g Junggar-Harlik, Onon...); they are composed by neoformed island arcs and their accretionnary margins. The Paleozoic oceanic framework of the peri-Siberia and North China/Tarim area was dominated by the Paleoasian, the Khanty-Mansi and the Mongol-Okhotsk oceanic plates, but many other oceanic basins, often smaller, had also an important role (e.g. Dzhida, Bayanhongor, Hengenshan...). Beside the cratonal North China/Tarim and Siberian plates, plates composed of microcontinents (e.g. Kazakhstan and South Mongolian plates) grew up also by accreting material during the whole Paleozoic. Proceeding by steps of 10-20Ma, we reconstructed and monitored the evolution of the oceanic realms and the geological history of each terranes involved in the formation of the Central Asian Orogenic Belt, until the final Late Paleozoic closure.

 

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