北京平原区晚中生代安山岩锆石U-Pb年代学及其地质意义  

Zircon geochronology and its structural implications of Late Mesozoic andesite from the Beijing plain

作　　者：渠洪杰[1,2] 王尔国 张磊[4] 李海龙[2] 康艳丽[2] 胡健民[2] 

机构地区：[1]北京探矿工程研究所地质调查研究室,北京100083 [2]中国地质科学院地质力学研究所,北京100081 [3]北京市地质矿产勘查开发总公司,北京100050 [4]北京市地质调查研究院,北京102206

出　　处：《岩石学报》2016年第11期3547-3556,共10页Acta Petrologica Sinica

基　　金：国家自然科学青年基金项目(41102057);中国地质调查项目(1212011121095)联合资助

摘　　要：本文对北京平原区Jr173井和Jr176井安山岩进行了SHRIMP和LA-LCP-MS锆石U-Pb定年,用以精确限定北京平原区火山岩时代、盆地形成与地貌转变之间的关系。2个安山岩中的锆石多晶型良好,具有典型的生长环带和较高的Th/U比值,显示其为岩浆锆石。Jr173井底部安山岩14颗锆石的206Pb/238U年龄可分为两组,其加权平均年龄分别为122.6Ma和138.4Ma;Jr176底部安山岩53颗锆石的206Pb/238U加权平均年龄为122.63Ma,表明该期火山岩的形成时代为早白垩世晚期,与前人认为的侏罗纪有较大区别。结合前人资料,北京地区沿着黄庄-高丽营断裂一线形成断陷盆地,西部隆升为山脉,东部下降为平原,就其安山岩喷发时代、空间展布和盆地发育特征而言,可视为中国东部晚中生代构造演化的一个缩影。This paper presents zircon SHRIMP U-Pb age of Well Jr173 and LA-LCP-MS U-Pb age of Well Jr176 andesite samples in the Beijing plain, to constrain the volcanic rocks formation time and their relation to the transformation of geomorphology in Beijing. Zircon grains from the two andesite samples are euhedral the subhedral in shape and show the typical oscillatory zoning with high Th/U ratios, implying that they should be magmatic in origin. The weighted mean 206pb/238u ages of two group＇s zircons from the andesite sample of Well Jr173 are 122. 6 and 138.4Ma, respectively. Zircon grains in Well Jr176 show weighted mean 2066pb/23s U age of 122. 63Ma, indicating that the volcanic rocks were formed in late stage of Early Cretacesous rather than Jurassic as previously believed. Based on the spatial variations of ages of the Mesozoic volcanic rocks and characteristics of basin, it is suggested that the formation and evolution in Beijing area are microcosm of basin-mountain pattern in eastern of China.

关 键 词：北京平原 安山岩 锆石U-Pb定年 早白垩世 黄庄.高丽营断裂 伸展盆地 

分 类 号：P588.144[天文地球—岩石学] P597.3[天文地球—地质学]