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北京密云元古宙常州沟组之下环斑花岗岩古风化壳岩石的发现及其碎屑锆石年龄
引用本文:和政军,牛宝贵,张新元,赵磊,刘仁燕.北京密云元古宙常州沟组之下环斑花岗岩古风化壳岩石的发现及其碎屑锆石年龄[J].地质通报,2011,30(5):798-802.
作者姓名:和政军  牛宝贵  张新元  赵磊  刘仁燕
作者单位:1. 中国地质科学院地质研究所,北京,100037
2. 中国地质调查局发展研究中心,北京,100037
基金项目:国家自然科学基会项目,中国地质调查局项目,中国地质调查局项目
摘    要:在北京密云地区,最近发现环斑花岗岩(脉)上发育有古风化壳,并被长城系常州沟组砂岩覆盖。风化壳物质的组成主要为来自环斑花岗岩的原地风化残留物和粗碎屑岩,采用SHRIMP和LA-ICP-MS方法,分别获得环斑花岗岩古风化壳碎屑岩的碎屑锆石U-Pb年龄值为(1682±20)Ma、(1708±6)Ma等,与相邻的密云环斑花岗岩年龄相同。这套古风化壳碎屑岩的存在和测年结果显示,长城系常州沟组的底界年龄应小于1682Ma。

关 键 词:古风化壳岩石  环斑花岗岩  碎屑锆石SHRIMP和LA-ICP-MS测年  长城系常州沟组  中元古界  北京

Discovery of the paleo-weathered mantle of the rapakivi granite covered by the Proterozoic Changzhougou Formation in the Miyun area,Beijing and their detrital zircon dating
HE Zheng-jun,NIU Bao-gui,ZHANG Xin-yuan,ZHAO Lei,LIU Pen-yan.Discovery of the paleo-weathered mantle of the rapakivi granite covered by the Proterozoic Changzhougou Formation in the Miyun area,Beijing and their detrital zircon dating[J].Geologcal Bulletin OF China,2011,30(5):798-802.
Authors:HE Zheng-jun  NIU Bao-gui  ZHANG Xin-yuan  ZHAO Lei  LIU Pen-yan
Affiliation:HE Zheng-jun1,NIU Bao-gui1,ZHANG Xin-yuan2,ZHAO Lei1,LIU Ren-yan1 1.Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China,2.Development Research Center of China Geological Survey
Abstract:Recently, the Proterozoic rapakivi granites (dike) with the paleo-weathered mantle-clastic rocks covered directly by the sandstones of the Changzhougou Formation of Changchengian System are discovered in the Miyun County, Beijing. The detrital components of the rocks embrace the in-situ weathered mantle saprolites and coarse-grained clastic rocks from rapakivi granites. Through SHRIMP and LA-ICP-MS dating methods, we have obtained the U-Pb dating ages of 1682±20 Ma and 1708±6 Ma from the detrital zircons sampled in the rocks; those age data are the same with the nearby Miyun rapakivi granite. The existence of this suite of weathered saprolites and clastic rocks, as well as the analysis of the dating results, have shown that the age of the base of the Changzhougou Formation should be younger than 1682 Ma.
Keywords:paleo-weathering mantle rocks  rapakivi granite  detrital zircon SHRIMP and LA-ICP-MS dating  Changzhougou Formation of Changchengian System  Mesoproterozoic  Beijing
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