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EARLY PALAEOZOIC SEDIM ENTATION AND TECTONIC EVOLUTION IN QINLING

Mei Zhichao, Cui Zhilin, Meng Qingren, Qu Hongjun   

  1. Departmem of Geology, Northwest University, Xi’an, 710069
  • Received:1995-06-20 Revised:1995-06-20 Online:1995-12-20 Published:1995-12-20

Abstract: The Qinlng orogenic belt has a complex evolutionary history. During early Palaeozioic time, the Southern Qinling was a passive continental margin of the Yangtze Plate, whereas the Northern Qinling became an active continental margin with the northward subduction of oceanic crust to the south. The belt underwent two great transgressive-regressive events. The first event occurred in the Cambrian and up to the Early Arenig, and the second one took place in the Late Arenig up to the Silurian. Thick platform carbonares in Zhenan Xichuan of the Southern Qinling and the North China Craton, and widespread pelagic and hemipelagic sediments composed of radiolarian cherts, siliceous and carbonaceous slates in oceanic or rift basins, suggesting that the Qinling area was in general in a spreading stage during the Early Palaeozoic Era. The uplift and denudation in the southern margin of the North China Craton during the Middle Arching and the appearance of a deep-water rift basin in the southwestern margin of the North China Craton in the Caradoc might be related to plate subduction. From the Late Ordovician to the Silurian, a large-scale regression occurred in this area. In the wide area, south of the Shangdan suture zone, the tectonic deformation and foreland basin deposits related to Caledonia movement have not been found and the Silurian sediments are still characterized by quartz sandstone with high maturity. Thus, we consider that the collision orogenesis did not occurred in this time,and this regression was probably related to the global sea—level descending.