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The metasedimentary rocks from the eastern margin of the Tarim Craton:Petrology,geochemistry,zircon U-Pb dating,Hf isotopes and tectonic implications

The metasedimentary rocks from the eastern margin of the Tar...

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中国科学院地质与地球物理研究所2013年度（第13届）学术年会

作者： Zhong-Mei Wang Chun-Ming Han Ben-Xun Su Patrick Asamoah Sakyi Sanjeewa P.K.Malaviarachchi Song-Jian Ao Luo-Juan Wang State Key Laboratory of Lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of Sciences University of Chinese Academy of Sciences Department of Earth Science University of Ghana Department of Geology Faculty of ScienceUniversity of Peradeniya State Key Laboratory of Lithosphefic Evolution Institute of Geology and GeophysicsChinese Academy of Sciences

The Dunhuang Block,located in the eastern Tarim Craton,widely exposes Precambrian TTG gneisses and metamorphosed supracrustal rocks.A suite of metasedimentary rocks of the Dunhuang Group in the Hongliuxia area on the eastern margin of the Tarim Craton are characterized by moderate contents of quartz,plagiodase,and biotite,with minor amounts of garnet or kyanite,most of which have experienced strong deformation,resulting in welldeveloped amphibolite-facies *** examined samples are characterized by moderate FeO+MgO and TiO contents,and AlO/SiO and KO/NaO ratios with low Chemical Index of Alteration(CIA)and high Index of Compositional Variability(ICV)values,suggesting that the protolith sediments originated from continental island arc *** U-Pb ages of magmatic-type detrital zircons from the Hongliuxia metasedimentary rocks range between 2476 Ma and 1950 Ma,with a peak at 2417 *** zircons of metamorphic origin yielded an age peak at 1832 Ma,which may represent a tectono-thermal event in the Paleoproterozoic,Considering that the main age populations of the analyzed samples are consistent with the tectono-thermal events in the Tarim Craton during the early Paleoproterozoic,we propose that the Tarim Craton was possibly the major source for the protolith sediments of the metasedimentary rocks in the Hongliuxia area,Zircon Hf isotopic compositions (ε(t)=-5.8 to+2.9)suggest voluminous addition of juvenile materials to the crust and minor reworking of old materials in the eastern Tarim Craton during the Mesoarchean(T=2.8-2.9 Ga).The metasedimentary rocks of the Hongliuxia area provide dear constraints to the evolution of the Tarim Craton,A possible tectonic model is that multiple thermal events(～2.4 Ga,2.2 Ga,2.0 Ga and 1.8 Ga)occurred in the study area,and the time period of Mesoarchean was important for crustal growth in the eastern Tarim Craton,whereas the～1.83 Ga metamorphism might represent a thermal event assodated with the Tarim Craton wit

关键词： Tarim Craton Metasedimentary rocks Provenance Zircon U-Pb dating hfisotopes

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Geochemistry and zircon U-Pb chronology of charnockites in the Yinshan Block,North China Craton:tectonic evolution involving Neoarchaean ridge subduction

Geochemistry and zircon U-Pb chronology of charnockites in t...

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中国科学院地质与地球物理研究所2013年度（第13届）学术年会

作者： Xudong Ma Hong-Rui Fan M.Santosh Jinghui Guo Key Laboratory of Mineral Resources Institute of Geology and GeophysicsChinese Academy of Sciences School of Earth Sciences and Resources China University of Geosciences Beijing State Key Laboratory of Lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of Sciences

The Yinshan Block,part of the Neoarchaean basement of the Western Block of the North China Craton,is composed of granite-greenstone and granulite-charnockite *** report research on a suite of charnockites from the gran- ulite-charnockite complex and characterize their geochemistry,zircon U-Pb geochronology,and Hf isotopic composition. The charnockites can be divided into intermediate(SiO=59-63 wt.%)and silicic(SiO=69-71 wt.%)groups.U-Pb zircon data yield protolith formation ages of 2524±4 Ma.2533±15 Ma,followed by metamorphism at 2498±3 Ma, 2490±11 Ma,respectively,for these *** the intermediate chamockites are characterized by higher AlO, TiO,FeO,MnO,MgO,CaO,PO,KO,Sr,and FREE content than the silicic charnockites,the ages and Hf isotopic composition of zircons and REE patterns of both intermediate and silicic charnockites are remarkably *** indicates that they are genetically *** chamockites are predominantly metaluminous to slightly peraluminous, calc-alkalic to calcic,and magnesian一characteristics generally related to a subduction ***-Sr+Ba granites with low KO/NaO characteristics,shown by these charnockites,imply a mixture of matiic and felsic magmas generated from an enriched mantle+lower *** MgO,Ni,Cr and Mg#,low KO/NaO,and metaluminous to slightly peraluminous natures imply that the source rocks most likely were *** calc-alkaline magmatism and high-T granulitefacies metamorphism under low-HO activity in the area lead us to propose a model involving mid-ocean ridge subduction within a Neoarchaean convergent *** arc-related rocks accreted along the continent margin,and became a barrier when the lithospheric mantle ascended through the slab *** derived from the decompressing mantle mixed with melt derived from the overlying,juvenile lower crust melt,which was warmed and metamorphosed by the ascending lithospheric mantle.

关键词： end of Archaean charnockites hfisotopes zircon U-Pb geochronology Yinshan Block North China Craton

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