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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.

Reclassification of the Meso- and NeoproterozoicChronostratigraphy of North China by SHRIMP Zircon Ages [查看] GAOLinzhi、ZHANGChuanheng、LIUPengju、TANGFeng、SONGBiao、DINGXiaozhong

High-quality zircon U-Pb ages acquried from Meso-and Neoproterozoic strata in North China in recent years has provided a hig-resolution chronostratigraphic famework for dating.A basis of this hig-level chronostratigraphic system provides the foundation for a global Precambrian study and stratigraphic correlation and so recent geological studies have focused attention on systemic SHRIMP zircon dating.A chronology of Meso-and Neoproterozoic strata and the time of origin of the overlying Changcheng System is given on the basis of new SHRIMP zircon dating from the Qianxi Complex and diabase of the Chuanlinggou Formation.A new tectonostratigraphy for a Neoproterozoic chronostratigraphic framework in the southeastern margin of the North CHina continent is underpinned by the new SHRIMP zircon dating of Neoproterozoic mafic magma diabase in the Jiao-LIao-Xu-Huai Sub-Province.

Report on 3.4 Ga SHRIMP Zircon Age from the Yuntaishan Geopark in Jiaozuo, Henan Province [查看] GAOLinzhi、ZHAOTing、WANYusheng、ZHAOXun、MAYinsheng、YANGShouzheng

Using the reported new U-Pb age with the Sensitive High-Resolution Ion hlicroprobe (SHRIRIP-II), zircon U-Pb ages were obtained from two samples of K-feldspar felsic paragneiss and K-feldspar gneissoid trondhjemite on the southern margin of the Taihang hlountains in the North China Craton. The protolith of the K-feldspar felsic paragneiss is argillaceous-sandy clastic sedimentary rock, probably deposited in the Neoarchean. Most of the detritus zircons show heavy loss of Pb. Five spots of zircons near the upper point, yield a weighted mean 207Pb/206Pb age of 3399±8 Ma, representing an age of the sedimentary source. Two groups of zircons from the K-feldspar gneissoid trondhjemite give weighted mean 207Pb/206Pb ages of 2511±13 Ma and 2735±16 Ma respectively. The former represents the emplacement time of the pluton, while the latter is interpreted as the age of the inherited zircons. The new data support that the Archean geological body in the central zone has an affinity with those from the eastern block of the North China Craton.

A New SHRIMP Age of the Xiamaling Formation in the North China Plate and Its Geological Significance [查看] GAOLinzhi、ZHANGChuanheng、SHIXiaoying、ZHOUHongrui、WANGZiqiang、SONGBiao

Setting up the hypostratotype of late Precambrian is the main aim of the research on the meso-and Neoproterozoic in North China.The chronostratigraphic position is the key in this study,However,many key horizons have not been calibrated with the high-quality isotopic ages.Using the reported new U-Pb age with the Sensitive High-Resolution Ion Microprobe(SHRIMP II),a zircon U-Pb age was obtained of the ash bed in the Xiamaling Formation in North China Plate,yielding a weighted mean 206Pb/238U age of 1368±12Ma.It is the first SHRIMP U-Pb age from the Ciamaling Formation in the North China Plate,and represents the depositing time of the middle part of the Xiamaling Formation.The zircon age plays an important role to understanding geological evolution of the North China Plate during Meso-and Neoproterozoic.

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.

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