冀西北晚侏罗世辉绿岩的发现对华北克拉通破坏过程的启示  

The discovery of Late Jurassic diabase in northwestern Hebei Province and its implications on the destruction of the North China Craton

作　　者：孟家葆 白春东 李泽阳 许凡 MENG Jiabao;BAI Chundong;LI Zeyang;XU Fan(Hebei Regional Geological Survey,Langfang,Hebei,065000)

机构地区：[1]河北省区域地质调查院,河北廊坊065000

出　　处：《地质论评》2025年第2期392-404,共13页Geological Review

基　　金：河北省自然资源厅“河北省沙岭子、宣化县、深井镇、涿鹿县1∶5万区域地质调查”的成果

摘　　要：前人对晚侏罗世时期华北克拉通的大地构造背景和岩石圈地幔性质转变时间的认识存在分歧。笔者等在华北克拉通北缘张家口市宣化区一带首次发现了晚侏罗世辉绿岩,对其开展地质学、岩石学、地球化学和同位素年代学研究,并对其构造背景进行了研究。本文在辉绿岩中获得LA-ICP-MS锆石U-Pb年龄为152.3±2.3 Ma,时代为晚侏罗世早期。辉绿岩SiO_(2)含量为48.99%~50.43%,K_(2)O含量为1.52%~2.04%;TiO_(2)含量为1.77%~2.05%,里特曼指数σ=3.64~5.78,镁指数Mg^(#)=43~46,其属于大陆板内碱性玄武岩系列。稀土总量ΣREE=211.55×10^(-6)~261.36×10^(-6);LREE/HREE为11.36~12.11,(La/Yb)_(N)=13.92~18.09,(Gd/Yb)_(N)=2.44~3.12,轻重稀土分馏强烈,重稀土分馏强烈;δEu=0.91~1.0,具微弱负铕异常—无异常。晚侏罗世辉绿岩形成于大陆板内拉张环境,属于洋岛型镁铁质岩浆岩,地幔源区为古亚洲洋俯冲洋壳改造的大洋型原始地幔。冀西北晚侏罗世辉绿岩为华北板块北缘首次发现,是区域上最早的古太平洋板块回撤的地质记录。Objective:There are differences in the understanding of the tectonic background and the transition time of lithospheric mantle properties of the North China Craton during the Late Jurassic Epoch.Methods:The author first discovered Late Jurassic diabase in Xuanhua District,Zhangjiakou City,on the northern edge of the North China Craton.The author conducted geological,petrological,geochemical,and isotopic dating studies on diabase,and and studied tectonic background.Results:This article obtained a LA-ICP-MS U-Pb age of 152.3±2.3 Ma from the zircons in the diabase,dating back to the early Late Jurassic.The SiO_(2) content of diabase ranges from 48.99%to 50.43%,and K_(2)O content ranges from 1.52%to 2.04%;TiO_(2) content ranges from 1.77%to 2.05%,with Rittman indexσ=3.64 to 5.78,and magnesium index of Mg^(#)=43 to 46,belonging to the alkaline basalt series within the continental plate.Total rare earth elements contentΣREE=211.55×10^(-6) to 261.36×10^(-6);LREE/HREE ranges from 11.36 to 12.11,(La/Yb)_(N)=13.92 to 18.09,(Gd/Yb)_(N)=2.44 to 3.12,with strong light and heavy rare earth fractionation and strong heavy rare earth elements fractionation;δEu=0.91 to 1.0,with weak negative europium anomalies to no anomalies.Conclusions:The Late Jurassic diabase was formed in the extensional environment within the continental plate and belongs to the oceanic island type mafic magmatic rock.The mantle source area of diabase is the oceanic primitive mantle modified by subducted of oceanic crust in ancient Asian Ocean.The Late Jurassic diabase in northwest Hebei Province was first discovered on the northern edge of the North China Craton,and is the earliest geological record of the retreat of the ancient Pacific Plate in the region.

关 键 词：华北克拉通减薄 晚侏罗世辉绿岩 板内环境 大洋型地幔 

分 类 号：P61[天文地球—矿床学]