| 华北古陆中、新元古代年代地层框架SHRIMP锆石年龄新依据 |
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| 关键词:North China Old Land Meso-Neoproterozoic strata Dahongyu Formation Xiamaling Formation SHRIMP dating |
| 基金项目:科技基础性工作专项(编号:2006FY120300-1); 中国地质调查局项目(编号:1212010511607,1212010511702); 自然科学基金项目(编号:40621002); 北京市教改项目 |
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| SHRIMP Zircon Ages: Basis for Refining the Chronostratigraphic Classification of the Meso-and Neoproterozoic Strata in North China Old Land |
| An important progress has been achieved in the completion of the Meso-Neoproterozoic hypostratotype section in Jixian.However,lots of key horizons have not yet been calibrated with the high-quality isotopic ages,which has a remarkable influence upon the competitiveness of GSSA in the Jixian section.A zircon U-Pb age was first obtained for the ash bed in the upper part of the Jixian section,yielding a weighted mean 207Pb/206Pb age of(1368±12) Ma(by Gao Linzhi et al.,2007;analyzed in Beijing SHRIMP Center).In addition,the new age of the Dahongyu Formation(1625.9±8.9) Ma in the Jixian section and that of the Xiamaling Formation(1370±11) Ma in Western Hills of Beijing were obtained and then examined by the SHRIMP Center in Curtin University,Perth,Western Australia.A breakthrough was made in Meso-Neoproterozoic chronostratigraphic research,and the location of the Jixian section was restored in the geological chart.At the same time,a new Meso-Neoproterozoic classification was advanced for the Jixian section.The SHRIMP zircon ages((1368±12) Ma and (1370±11) Ma) have raised new problems before us,and Chinese geologists must face the following challenges: ① The top boundary age of the Tieling Formation is limited at 1400 Ma or younger.② The time limit of the hypostratotype of the Changcheng and Jixian systems may be in 1800～1200 Ma,not in 1800～1000 Ma.According to the age of the Xiamaling Formation,the Changcheng System is limited in 1800～1600 Ma and the Jixian System is in 1600～1400 Ma,being respectively the lower and the middle part of Mesoproterozoic strata.③ The dating serves as evidence of chronostratigraphy for diabase dikes,which are well developed in Meso-and Neoproterozoic strata in the North China Old Land.The strata of 1200～800 Ma in the Yangtze Platform and on the southern margin of the North China Old Land should be further investigated and interpreted.However,the zircon dating is an important achievement of the Precambrian chronostratigraphy in China,which increases the international competitiveness of the Jixian section. |
| GAO Lin-zhi,ZHANG Chuan-heng,YIN Chong-yu,SHI Xiao-ming,WANG Zi-qiang,LIU Yao-ming,LIU Peng-ju,TANG Feng,SONG Biao.2008.SHRIMP Zircon Ages: Basis for Refining the Chronostratigraphic Classification of the Meso-and Neoproterozoic Strata in North China Old Land[J].Acta Geoscientica Sinica,29(3):366-376. |
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