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Regional Tectonic Transformation in East Kunlun Orogenic Belt in Early Paleozoic: Constraints from the Geochronology and Geochemistry of Helegangnaren Alkali-feldspar Granite
作者姓名:LI Ruibao  PEI Xianzhi  LI Zhuochen  SUN Yu  PEI Lei  CHEN Guochao  CHEN Youxin  LIU Chengjun and WEI Fanghui
作者单位:1 School of Earth Science and Resources, Chang’an University, Xi’an 710054, China;2 Key Laboratory of Western China’s Mineral Resources and Geological Engineering, Ministry of Education, Xi’an 710054, China;3 National Key Laboratory of Remote Sensing Information and Image Analysis Technology, Beijing Research Institute of Uranium Geology, Beijing 100029, China;4 School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China
基金项目:The work is financially supported by National Natural Science Foundation of China (Grant Nos. 41172186, 40972136 and 40572121), Special Fund for Basic Scientific Research of Central Colleges, Chang’an University, China (Grant Nos. CHD2011TD020, CHD2009JC070, CHD2009JC053 and CHD2009JC046), the Commonweal Geological Survey, the Aluminum Corporation of China and the Land-Resources Department of Qinghai Province (Grant No. 200801).
摘    要:The Helegangnaren feldspar granite exposed in the eastern part of East Kunlun, is characterized by high concentrations of SiO2 and alkaline, low abundances of Fe, Mg and Ca, metaluminous-weak peraluminous. Trace elements analysis shows that the granite is depleted extremely in Ba, Sr and Eu, and rich in some large-ion lithophile elements and high field strength elements. Besides, the granite has high Ga contents, the values of 104(Ga/Al) vary from 2.50 to 2.77, which is mainly greater than the lower limit of A-type granites (2.6), and is higher than the I- and S-type granites’ average (2.1 and 2.28, respectively). Rare earth element (REE) is characterized by relatively high fractionations of light REE (LREE) and heavy REE (HREE) (LREE/HREE=9.3–13.60, (La/Yb)N=10.92–18.02), pronounced negative Eu anomalies (δEu=0.08–0.13), and exhibits right-dipping gull pattern. Major elements, rare elements and trace elements features show the granite is ascribed to A-type granite and A2 subtype in tectonic genetic type. They are plotted into post-collision or within-plate area in a variety of tectonic discriminations. Geological and geochemical data comprehensively suggest that the granite is formed in a post-collision extensive tectonic setting. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating yields a weighted mean age of 425?Ma, belonging to Middle Silurian, which is similar to the age of the post-collision geological events in the region. The differences of magmatic rocks in formation age, rocks assemblage and rocks series systematically indicate that the regional tectonic stress regime in the East Kunlun orogenic belt experienced a major transformation from compress to extension in Middle Silurianin, and the Helegangnaren feldspar granite intruded in the early stage of tectonic transformation.

关 键 词:A-type  granite    post  orogeny    compound  orogeny    East  Kunlun
收稿时间:6/6/2012 12:00:00 AM
修稿时间:2012/11/22 0:00:00

Regional Tectonic Transformation in East Kunlun Orogenic Belt in Early Paleozoic: Constraints from the Geochronology and Geochemistry of Helegangnaren Alkali-feldspar Granite
Authors:LI Ruibao  PEI Xianzhi  LI Zhuochen  SUN Yu  PEI Lei  CHEN Guochao  CHEN Youxin
Institution:1. School of Earth Science and Resources, Chang'an University, Xi'an 710054, China;Key Laboratory of Western China's Mineral Resources and Geological Engineering, Ministry of Education,Xi'an 710054, China
2. National Key Laboratory of Remote Sensing Information and Image Analysis Technology, Beijing Research Institute of Uranium Geology, Beijing 100029, China
3. School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China
4. School of Earth Science and Resources, Chang'an University, Xi'an 710054, China
Abstract:The Helegangnaren feldspar granite exposed in the eastern part of East Kunlun, is characterized by high concentrations of SiO2 and alkaline, low abundances of Fe, Mg and Ca, metaluminous‐weak peraluminous. Trace elements analysis shows that the granite is depleted extremely in Ba, Sr and Eu, and rich in some large‐ion lithophile elements and high field strength elements. Besides, the granite has high Ga contents, the values of 104(Ga/Al) vary from 2.50 to 2.77, which is mainly greater than the lower limit of A‐type granites (2.6), and is higher than the I‐ and S‐type granites’ average (2.1 and 2.28, respectively). Rare earth element (REE) is characterized by relatively high fractionations of light REE (LREE) and heavy REE (HREE) (LREE/HREE=9.3–13.60, (La/Yb)N=10.92–18.02), pronounced negative Eu anomalies (δEu=0.08–0.13), and exhibits right‐dipping gull pattern. Major elements, rare elements and trace elements features show the granite is ascribed to A‐type granite and A2 subtype in tectonic genetic type. They are plotted into post‐collision or within‐plate area in a variety of tectonic discriminations. Geological and geochemical data comprehensively suggest that the granite is formed in a post‐collision extensive tectonic setting. Laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) zircon U‐Pb dating yields a weighted mean age of 425 Ma, belonging to Middle Silurian, which is similar to the age of the post‐collision geological events in the region. The differences of magmatic rocks in formation age, rocks assemblage and rocks series systematically indicate that the regional tectonic stress regime in the East Kunlun orogenic belt experienced a major transformation from compress to extension in Middle Silurianin, and the Helegangnaren feldspar granite intruded in the early stage of tectonic transformation.
Keywords:A-type granite  post orogeny  compound orogeny  East Kunlun
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