Two-Phase Magmatic Events during Late Paleozoic in the North of the Central Inner Mongolia-Da Hinggan Orogenic Belt and Its Tectonic Significace
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    Abstract:

    The Inner Mongolia-Da Hinggan Orogenic Belt, located in the eastern segment of Central Asian Orogenic Belt, has long been a focus study region for geologists. The Bayanwula area in the north of Sonid Zuoqi, is characterized by the volcano-sedimentary strata of the Baolige Formation and felsic intrusive rocks. By means of zircon LA-ICP-MS U-Pb dating, the age of volcanic rocks in the Aershanbaolag region abtained (310.5±0.78 Ma) that is consistent with the previous ages of the Baolige Formation rocks around the Bayanwula village(307.1±6.3 Ma, 308.9±1.8 Ma). It turns out that the Baolige Formation strata formed during Late Carboniferous. The age of granite porphyry dyke is 286.6±0.75 Ma, and the granodiorite to the south region is 312.5±0.75 Ma. They all formed during the Late Carboniferous-Early Permian. Combined with the regional geology analysis, there are two crucial phases of magmatic activities in the north of the central IMDOB, with the peak ages of 318 Ma and 281 Ma. Geochemical data show that the volcanic rocks in the Baolige Formation are characterized by a transitional feature from low-K tholeiitic to calcium alkaline and alkaline series, mainly being in the calcium alkaline and alkaline series. Moreover the Early-Permian granite porphyries belonging to the A-type granite, are similar to the A-type granites in the Xinlinhot area and Bayanwula-Dong Ujimqin Banner belt. In the tectonic discrimination diagrams of granites, all the granite porphyries fall into the post-orogenic area. Meanwhile the tectonic environment of magmas develope toward a post-orogenic setting in the diagrams and the K2O content increase gradually in the SiO2 vs K2O and Na2O vs K2O diagrams from the Late Carboniferous to the Early Permian, which imply a stable within-plate geological setting. In addition, these Late Paleozoic magmatic activities probobly were related to the formation of the Erlian-Hegenshan ophiolite complex belt. The Late Carboniferous magmas developed in a post-orogenic setting. Along with the occurrence of volume A-type granites, alkaline magmas and bimodal volcanic rocks, the tectonic environment changed into a widespread extensional regime in Early Permian.

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LI Ke, ZHANG Zhicheng, FENG Zhishuo, LI Jianfeng, TANG Wenhao, LUO Zhiwen, CHEN Yan.2015. Two-Phase Magmatic Events during Late Paleozoic in the North of the Central Inner Mongolia-Da Hinggan Orogenic Belt and Its Tectonic Significace[J]. Acta Geologica Sinica,89(2):272-288

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History
  • Received:December 27,2013
  • Revised:April 28,2014
  • Adopted:February 12,2015
  • Online: February 12,2015
  • Published: