上海基底地层格架的锆石LA-ICP-MS U-Pb年龄及微体化石特征制约  

Zircon LA-ICP-MS U-Pb ages and microfossil characteristics constraintsof the Shanghai basement stratigraphic framework

作　　者：谢建磊[1] XIE Jianlei(Shanghai Institute of Geological Survey,Shanghai 200072,China)

机构地区：[1]上海市地质调查研究院,上海200072

出　　处：《上海国土资源》2023年第3期12-22,共11页Shanghai Land & Resources

基　　金：中国地质科学院科研项目“上海区域地质调查片区总结与服务产品开发”(DD20160345-07)。

摘　　要：基底地层特征对构造单元和地震地质背景认识具有重要意义。上海位于扬子克拉通和华夏造山系的交界区,同时位于江南造山带北东侧,构造位置比较特殊,但长期以来对其基底地层特征的认识比较薄弱。本文对典型钻孔揭露的变质岩、凝灰岩开展了锆石LA-ICP-MS U-Pb定年和疑源类化石分析,斜长角闪岩和花岗质糜棱岩分别获得1091.1±8.8 Ma、1753±24 Ma的原岩年龄,片麻岩获得上交点年龄2445±27 Ma、下交点年龄581±110 Ma,安山质糜棱岩206Pb/238U谐和年龄有2708~2447 Ma、1371~1097 Ma和956~903 Ma三个区间,凝灰岩获得801±13 Ma、774±12 Ma的原岩年龄,板岩中含较多炭化剧烈的Leiosphaeridia化石。认为区内基底自下而上可划分出金山群、惠南板岩和河上镇群,分别形成于古元古代初期—中元古代、青白口纪早—中期和青白口纪晚期,总体年龄特征表现出与华夏造山系的亲缘性特征。2447~2507 Ma、1753 Ma、1091.1 Ma、801~774 Ma和581±110 Ma等建造和改造事件是对凯若兰超大陆、哥伦比亚超大陆、罗迪尼亚超大陆和冈瓦纳超大陆汇聚裂解过程的响应。The characteristics of the basement strata are important for understanding tectonic units and seismic geological background.Shanghai is located at the junction of the Yangtze Craton and Cathaysia orogenic system,as well as on the northeast side of the Jiangnan orogenic belt.Despite the special tectonic location,knowledge of its basement strata has been limited for a long time.Herein,laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)uranium-lead zircon dating and fossil analysis of metamorphic rocks and tuff exposed to typical boreholes were performed.The protolith ages of plagioamphibolite and granitic mylonite are 1091.1±8.8 Ma and 1753±24 Ma,respectively.The upper and lower intersection age of gneisses is 2445±27 Ma and 581±110 Ma,respectively.The 206Pb/238U concordance ages of the andesitic mylonite is 2708~2447 Ma,1371~1097 Ma,and 956~903 Ma.The protolith ages of the tuff are 801±13 Ma and 774±12 Ma,and the slate contains more intense carbonization Leiosphaeridia fossils.The basement of this area can be divided into the Jinshan group,Huinan slate,and Heshangzhen group,which were formed during the early Paleoproterozoic-Middle Proterozoic,early middle Qingbaikou,and late Qingbaikou periods,respectively.The general age characteristics show an affinity between the basement and the Cathaysia orogenic system.The construction and modification events,such as 2447~2507 Ma,1753 Ma,1091.1 Ma,801~774 Ma,and 581±110 Ma,were in response to the convergence and breakup of the Kenorland,Colombian,Rodinia,and Gondwana supercontinents.

关 键 词：基岩地质 基底地层 锆石定年 微体化石 金山群 惠南板岩 河上镇群 

分 类 号：P535[天文地球—古生物学与地层学]