LA-MC-ICP-MS Zircon U-Pb Dating of the Volcanic Rocks from the Gegen Obo Formation in East Ujimqin Banner Area, Inner Mongolia, and Its Significance
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摘要: 内蒙古东乌珠穆沁旗地区格根敖包组为一套海陆交互相中酸性火山岩、火山碎屑岩以及陆源碎屑岩组合,含有动植物化石。其时代具有争议。本文获得了格根敖包组二段火山岩LA-MC-ICP-MS锆石U-Pb年龄(307.3±0.99) Ma和(311.6±1.3) Ma,表明其形成于晚石炭世。结合前人古生物化石资料,认为格根敖包组上部(三、四、五段)陆源碎屑沉积地层,时代为早二叠世,而火山岩及其以下地层(一段、二段)属于晚石炭世。从而将格根敖包组形成时代限定为晚石炭—早二叠世。格根敖包组下部(一段、二段)地层与邻区宝力高庙组时代一致,同属晚石炭世。Abstract: The Gegen Obo Formation consists of intermediate-acidic lava and volcaniclastic as well as terrigenous clastic rocks, and is considered to be marine-continental alternative facies according to its abundant fossils and petrogenetic features. However, its age is still under discussion. The authors have obtained zircon LA-MC-ICP-MS U-Pb ages of (307.3±0.99) Ma and (311.6±1.3) Ma from volcanic rocks of the Gegen Obo Formation, suggesting Late Carboniferous. Combined with previous fossil evidence and stratigraphic studies of related rocks,the authors assigned the upper sediments of Gegen Obo Formation (member 3, 4 and 5) to Early Permian, and the lower part (member 1 and 2) to Late Carboniferous. Thus the age of Gegen Obo Formation is confined to late Carboniferous-early Permian. The lower parts (member 1 and 2) of Gegen Obo Formation and Baoligaomiao Formation have the same upper limit of age, both belonging to late Carboniferous.
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Key words:
- Gegen Obo Formation /
- Baoligaomiao Formation /
- East Ujimqin Banner
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