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Igneous Petrotectonic Assemblages and Tectonic Settings: A Discussion

DENG Jin-fu1, 2,XIAO Qing-hui 1, 2,SU Shang-guo1, 2,LIU Cui1,ZHAO Guo-chun1,WU Zong-xu1,LIU Yong1,2   

  1. 1. State Key Laboratory of Geological Processes and Mineral Resources, Key Laboratory of Lithosphere Tectonics and Lithoprobing Technology of Ministry of Education, China University of Geosciences, Beijing 100083, China;2. Development and Research Center, Survey Bureaus of China Geological, Beijing 100083, China
  • Received:2007-09-20 Revised:2007-09-20 Online:2007-09-20 Published:2007-09-20

Abstract: This paper discusses igneous petrotectonic assemblages of various tectonic settings: 1. mid–ocean ridge spreading; 2. oceanic island; 3. island arc; 4. MORS–type and SSZ–type ophiolites; 5. active coutineutal marginal arc; 6.compositional polarity of subduction–related magmatic arcs; 7. continental collision; 8. continental rift; 9. stable craton or platform, etc. It is emphasized that the tholeiitic ( TH ), calc–alkaline ( CA ) and alkaline ( A ) series defined from various parameters by different authors have different scientific meanings. In this paper it is indicated that the same written terms of TH, CA and A but with various meanings could easily result in abuse of these terms, especially for the recognition of the tectonic settings. The difference between MORS – and SSZ –type ophiolites in terms of igneous petrotectonic assemblages is discussed. The lowest MgOwt% of the HMA is suggested ( Table 2 ), based on the data of petrological experiments. The terms of magnesian andesite–dacite and adakite are discussed, and in turn, the Kay's magnesian andesite–dacite of higher Sr/Y, lower FeO/MgO, and higher MgOwt% as well as higher Ni, Cr contents, are comprehensively used, which can be more satisfactory to define the slab–melt, rather than the single parameter of high Sr/Y. The various schemes of classification for the continental collision are indicated, and it is necessary to be careful for using these schemes. The post–orogenic and the continental rifting A type granites are suggested to be associated with or without the CA/r, respectively, and the meaning of A and CA, here, is determined by the Peacock's alkali–lime index.