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MAJOR GEOLOGICAL EVENRI OF JINNING PERIOD AND THEIR TECTONIC SETTINGS IN THE NORTH QINLING

PEI Xian-zhi1;2, WANG Tao1;2, WANG Yang2, LI Hou-min2 LI Guo-guang2   

  1. 1. Department of Geology, Northwest University, Xi’an, 710069; 2. Xi’an Engineering University, Xi’an, 710054
  • Received:1999-06-20 Revised:1999-06-20 Online:1999-06-20 Published:1999-06-20

Abstract: The Proterozoic tectono-lithostratigraphic units in the North Qinling orogenic belt mainly include the QinLing complex of Paleo-Proterozoic,the Xiaba Group, Kuanping Group and Wuguan Group of the Mesoproterozoic, Songshugou ophiolite tectonic slice of the Late Mesoproterozoic, the Danfeng Group and lower part lithostratigraphic units of the Neoproterozoic Erlangping Group. The Qinling complex belongs to metamorphic crystalline basement(2 226~1 984Ma) of the North Qinling orogenic belt. The Xiahe Group(1 605 Ma), Kuanping Group(1 827~1 142Ma) and Wuguan Group(1 382Ma)were respectively formed in the tectonic settings of the active continent margin, back-arc small ocean basin and continent rift in the Mesoproterozoic. The Songshugou ophiolite was formed in small ocean-basin of the late Mesoproterozoic. The Danfeng Group(973~825Ma)and lower part of the Erlangping Group(948~708Ma)were formed respectively in the tectonic settings of the island-arc and back are-basin in the Neoproterozoic. Strong tectono-magmatic-metamorphic geological events of the Jinning period (1 000~800Ma) occurred widely in the North Qinling, which include island-arc-type basic-intermediate basic and granitic magmatism, collision type granitic magmatism, tectonic emplacement of the Songshugou ophiolite, regional and high-pressure metamorphism of the meta-geological bodies during main metamorphic stage (996~ 744Ma), strong structural deformation and tectonic superimposition, as we1l as intensive crust accretion. These geological events indicate that main body of the North Qinling was an ancient orogenic belt formed during the Neoproterozoic. Although these events may not suggest a direct subduction-collision integrating between the Yangtze block and North China block, they are evidences for a subduction-collision integrating between “the Middle Qinling micro-blocks” with characteristics of the Yangtze block basement and the North Qinling micro-block or the North China block. The continent breakup happened after the Sinian period in the Qinling region, which marked the beginning of the Pbanerozoic tectonic evolution stages. The major geological events of Jinning period(1 000~800Ma)and the tectonic history after the Sinian period in the Qinling orogenic belt ale coincidence with the formation of the Rodinia supercontincnt during the Neopmterozoic and breakup of the Rodinia supercontinent during 700~570Ma as suggested by some geologists.