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Petrological and Geochemical Studies on the Intermediate-Basic Volcanic Rocks from the Middle-South Part of the Da Hinggan Mountains

Lü Zhi-cheng1 2, DUAN Guo-zheng3, HAO Li-bo3, LI Dian-chao3, PAN Jun3, WU Feng-chang2   

  1. 1. Development and Research Center, China Geological Survey, Beijing 100037, China; 2. Open Lab. Of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China; 3. Jilin University, Changchun 130026, China
  • Received:2004-06-20 Revised:2004-06-20 Online:2004-06-20 Published:2004-06-20

Abstract: The petrogenesis and tectonic background of Mesozoic volcanic rocks from the middle-south part of the Da Hinggan Mountains are closely related to the late stage evolution of the Southem Mongolia-Da Hinggan Mountains orogenic belt and to the genesis of copper-polymetallic deposits.Based on detailed fieldwork,petrological and geochemical studies on volcanic rocks have been carried on.The results show that the volcanic rocks,including basaltic trachyte,trachyandesite,trachyte and dacite,belong to cale-alkaline series.In major elements they are enriched in Si02,Na20 and K20,and depleted in Fe203,FeO,MgO and CaO;and in trace elements they are enriched in lithophile elements,and depleted in siderophile elements and Nb,Ta,Ti etc.In REE patterns they are generally LREE enriched,(87Sr/86Sr)t ratios are 0.7045~0.7077,mostly 0.7045~0.7055,and most of εNd(t)values are positive.The results suggest that partial melting of upper mantle in different degrees Was the major mechanism for generation of the volcanic rocks in the middle-south part of the Da Hingan Mountains。and the volcanic rocks were developed in the tensional tectonic setting.The Mesozoic volcanic activity was a response to the extension caused by upwelling of mantle plume of asthenosphere during the post-orogenic period of the Tianshan-Da Hingan Mountains belt,to the post-orogenic extension background of the Inner Mongolia-Jihei orogenic belt,and to compression background caused by closure of Mongolia-Okhotsk residual ocean in a scissors form.