International Geologiical Congress - Oslo 2008

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ASI-02 Geology and mineral resources of Northern and Central Eurasia

 

Tectonic cycles and stages of continents: An example from NW China

 

Jinyi Li, Chinese Academy of Geological Sciences (China)
 

 

Plate tectonic theory being advent in 1960's is considered as Ocean Dynamics in which the tectonic evolution of oceans is summarized as the Wilson cycle. The theory is later used the reconstruction of continental tectonic evolution and made many puzzles be untied, but some perplexities remain.
Xinjiang province of China is located in the center of Asian continent. Available data reveal that the geological history of the region is composed of three tectonic cycles such as Archean- Paleo-proterozoic, Mid-proterozoic-middle Neo-proterozoic and later Neo-proterozoic-Cenozoic. The crust of the region was mainly formed in the third cycle and may be subdivided into Nanhua (755Ma620Ma)-Cambrian continental rifting and divergent stage, Ordovician to Carboniferous continental convergent stage, Late Carboniferous-Permian continental welding stage and Triassic-Quaternary continental stable developing stage. The above first two stages are on the whole equivalent to the Wilson cycle of the ocean, but the later two stages only occur in continental evolution.
Early Mid-proterozoic and the middle Neo-proterozoic bi-model magmatic activities and regional unconformities in the basal of both Mid-proterozoic-early Neo-proterozoic and middle Neo-proterozoic-Paleozoic marine sedimentary sequences in the northern margin of the Tarim basin represent the beginning of two Phanerozoic tectonic cycles of the supercontinental evolution in the central Asia. Occurrence of Ordovician Calcalkaline volcanic eruptions and plutonic magmatic intrusives in the Tianshan and Altay mountains mark the boundary of both stages of continental divergence and convergence. The latest Carboniferous intense regional compressive and strike-slipping deformation and intrusion and eruption of potash-rich acid-intermediate magma in the Tianshan mountains indicate the continental welding stage. In the intra-continental tectonic stage, uplifting and subsidence with occurrence of various basin-range frameworks and paneplanation, and intra-orogeny may took place which are originated from the plate collision in the surrounding margins of the continent or related to interaction between the lithosphere and asthenosphere within the continent.
In combination with available data from other continents on the earth, we suggest that the above tectonic cycles and stages of the continental geological history are suitable to reconstruction of the global continental tectonic evolution since the Paleo-proterozoic, maybe since the Archean. Evidently, tectonic cycles and states of continents are greatly different from those of oceans, which makes us get a primary inference that mantle-convection driving disintegration, divergence and convergence of continents, and anatexis and isostasy of thicken crusts in convergent belts within continents may be main dynamic processes of the continental evolution.

 

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