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    Detrital Zircon Dating of Meso-and Neoproterozoic Rocks in North China and Its Implications [查看] GAOLinzhi、LIUPengju、YINChongyu、ZHANGChuanheng、DINGXiaozhong、LIUYanxue、SONGBiao
    New dates from Meso-and Neoproterozoic strata contribute to the recently defined Orecambrian stratigraphical timescale of China agreed by the Subcommission on the Precambrian System,and the National Commission on Stratigraphy of CHina on Nov.24,2009.First,the age range of the Chingcheng System,including the Changzhougou,Chuanlinggou,Tuanshanzi and Dahongyu formations has been constrained to 1.8-1.6Ga.second,the Jinxian System including the Gaoyuzhuang,Yangzhuang,Wumishan,HOngshuizhuang and Tieling formations has been constrained to 1.6-1.4Ga.Third,an as-yet unnamed(undefined)system(1.4-1.0Ga)is only developed in the Xiamaling Formation at JIxian section,Tianjing.OFrth,the Qingbaikou System,including the Luotuoling and jing'eryu formationshas been constrained to 1.0-0.78Ga.Fifth,the Nanhuan System ranges betwwen 780-635Ma，and the Sinian System is within 635-542Ma,However,according to a series of SHRIMP U-Pb dates from the late Precambrian in the JIangnan Orogen Belt in South China Platform,the constrained strata will be redefined as in the upper part of the Qingkaikou SYstem.To aid global geodynamics,it is useful to denote a late Precambrain section with unified,precise and high-precision chronological dating;this is here defined in North China Block and Jiaoliao-Korean Block. However,the Neoproterozoic Qingkaikou study in North China will be influence in whole Meso-and Neoproterozoic in the Jiangnan Orogenic Belt in betwwen the Yangtze Block and the Cathaysia Block in South China.
    An Important Spreading Event of the Neo-Tethys Ocean during the Late Jurassic and Early CretaceousEvidence from Zircon U-Pb SHRIMP Dating on Diabase in Nagarze,Southern Tibet [查看] JIANGSihong、NIEFengjun、HUPeng、LIUYan
    Widely distributed in Gyangze-Chigu area,southern Tibet,NW-and nearly E-W-trending diabase(gabbro)-gabbro diorite dykes are regarded as the product of the large-scale spreading of the late Neo-Tethys Ocean.In order to constrain the emplacement age of these dykes,zircons of two samples from diabases in Nagarze were dated by using the U-Pb SHRIMP method.Two nearly the same weighted mean 206Pb/238Uages were obtained in this paper,which are 134.9±1.8Ma(MSWD=0.65)and 135.5±2.1(MSWD=1.4),respectively.They not only represent the crystallization age of the diabase,but also documented an important spreading event of the Neo-Tethys Ocean during the late Jurassic and early Cretaceous.This dating result is of great significance to reconstruct the temporal framework of the late Neo-Tethys Ocean in the Qinghai-Tibet Plateau.
    Zircon U-Pb dating for the earliest Neoproterozoic mafic magmatism in the southern margin of the North China Block [查看] LIUYongqing、GAOLinzhi、LIUYanxue、SONGBiao、WANGZongxiu
    Huge diabase occurs within the Pro-terozoic strata in the southern margin of the North China Block, geographically in the northern parts of Anhui and Jiangsu provinces, where no strata younger than Neoproterozoic have been found. Zir-cons from the diabase show three different structures from cathodoluminesecence imaging, but they are all of magmatic origin. SHRIMP U-Pb dating yields a range of 206Pb/238U ages from 2600 to 124 Ma, but two geological events can clearly be identified from both concordant and discordant ages. One gives two weighted mean 207Pb/206Pb ages of 976 ± 24 and 1038 ± 26 Ma which are interpreted as timing of dia-base crystallization, and the other has a weighted mean 207Pb/206Pb age of 2523 ± 52 Ma that repre-sents formation time of inherited zircon from the old crust. The dating results indicate that the mafic magmatic event occurred in a transition period from the latest Mesoproterozoic to the earliest Neopro-terozoic, consistent with global subduction of Grenvill ocean crust to result in the assembly of superconti-nent Rodinia. Therefore, the North China Block needs to be taken into account when reconstructing the position of China continents within the framework of Rodinia supercontinent.
    U-Pb zircon age for the Daohugou Biota at Ningcheng of Inner Mongolia and comments on related issues [查看] LIUYongqing、LIUYanxue、JIShu’an、YANGZhiqing
    SHRIMP U-Pb zircon dating was carried out for the Daohugou Biota near Ningcheng of Inner Mongolia and for lavas overlying or underlying sala-mander-bearing strata at Reshuitang in Lingyuan of West Liaoning. The results suggest that the Dao-hugou Biota occurred at an interval from 168 Ma to 164-152 Ma. Both the Daohugou Biota and the salamander-bearing fossil assemblage are the same biota and thus developed from 168 to 152 Ma, i.e. from late Middle Jurassic to the early Late Jurassic. The Daohugou Biota-bearing rocks, resting on the Jiulongshan Formation in disconformity and being overlain in unconformity by Late Jurassic Tuchengzi Formation and Early Cretaceous rocks containing the Jehol Biota, are mainly composed of volcanic-sedi-mentary rocks in a normal sequence. It is recom-mended that the Daohugou Biota and the related stratigraphy should be correlated with the Tiaojishan Formation (Lanqi Formation in West Liaoning) or its synchronous rocks. It is suggested that the Dao-hugou Biota and the Jehol Biota would be neither taken into one biota nor considered as the earliest elements of the Jehol Biota. The Daohugou Biota and the related rocks and the Yixian Formation were re-spectively formed in different periods of vol-canic-sedimentary tectonics.
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