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  

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

作　　者：和政军[1] 牛宝贵[1] 张新元[2] 赵磊[1] 刘仁燕[1] 

机构地区：[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

出　　处：《地质通报》2011年第5期798-802,共5页Geological Bulletin of China

基　　金：国家自然科学基金项目<冀西北尚义盆地的晚侏罗世同构造沉积响应>(批准号:40872081);中国地质调查局项目<亚洲三大构造域动力演化过程及其转化关系研究>(编号:1212010611808);<兴蒙造山带基本构造格局综合调查和研究>(编号:1212011085476)

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。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.

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 

分 类 号：P534.3[天文地球—古生物学与地层学] P597.3[天文地球—地质学]