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DEVONIAN MAGMATISM IN THE NORTHERN MARGIN OF THE NORTH CHINA BLOCK AND ITS TECTONIC SETTING

ZHANG Qiqi;ZHANG Shuanhong;Institute of Geomechanics,Chinese Academy of Geological Sciences;Key Laboratory of Paleomagnetism and Tectonic Reconstruction,Ministry of Natural Resources;  
Late Paleozoic-early Mesozoic magmatic rocks are widespread along the northern margin of the North China Block and constitute an east-west belt that is about one thousand kilometers long. As a part of the late Paleozoic-early Mesozoic magmatic belt,the distribution of the Devonian magmatic rocks is not common as that of the Carboniferous-Permian magmatic rocks. However,in recent years,more and moreDevonian magmatic rocks have been identified and their geological background and tectonic implications have been much more attractive than before. Our research in combined with previously published results indicate that the Devonian magantism along the northern North China Block occurred mainly during 400 ~360 Ma. Among them the Devonian alkaline intrusive rocks and mafic-ultramafic intrusive rocks are distributed along the northern North China Block from Guyang to Chifeng areas and their emplacement occurred mainly during 400 ~ 380 Ma. The Devonian volcanic rocks are mainly distributed in Chifeng area in the eastern part of the northern North China Block and their eruption occurred during two peaks at400 Ma and 360 Ma,respectively. The Devonian intrusive rocks consist mainly of monzonite,syenite and alkaline granite with minor monzodiorite and mafic-ultramafic rocks. The Devonian volcanic rocks are composed mainly of metamorphic rhyolitic rocks and metamorphic basaltic andesite, metabasalt( plagioclase amphibolite) and exhibit characteristics of bimodal volcanic rocks. Rock association,weak deformation fabrics,and geochemical and isotopic characteristics of the Devonian magmatic rocks,as well as the tectonic evolution history suggest that formation of the Devonian magmatic rocks in the northern North China Block is related to post-collisional extension after arc-continental collision between the Bainaimiao arc and the northern North China Craton during the latest Silurian. The Devonian magmatic rocks identified from the northern North China Block in recent years are of great significance to better understand the continental crustal growth of the northern margin of North China Block during late Paleozoic period and timing for final closure of the Paleo-Asian ocean.
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