华北克拉通和巴西圣弗朗西斯科-刚果克拉通新元古代早期岩浆作用(ca.940~890Ma)序列与成因  

Sequence and genesis of the Early Neoproterozoic magmatism(ca.940~890Ma)in the North China Craton and S o Francisco-Congo Craton

作　　者：苏向东 彭澎[2] SU XiangDong;PENG Peng(Geothermal and Ecological Geology Research Center,School of Ecology and Environment,Zhengzhou University,Zhengzhou 450001,China;China-Brazil Joint Geoscience Research Center,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]郑州大学生态与环境学院,地热与生态地质研究中心,郑州450001 [2]中国科学院地质与地球物理研究所,中国-巴西联合地学研究中心,北京100029

出　　处：《岩石学报》2025年第1期167-182,共16页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42302219);中国科学院前沿项目(QYZDB-SSWDQC04281712250)联合资助.

摘　　要：华北克拉通和巴西圣弗朗西斯科-刚果克拉通新元古代早期的岩墙和岩床及玄武岩(ca.940~890Ma)岩浆活动时间对比和古地磁研究结果表明,上述克拉通在新元古代可能相邻。这些阶段性岩浆作用的演化趋势和源区特征及其所反映的地质过程与构造背景对进一步开展大陆重建有重要意义。本文系统总结和对比分析了两个克拉通新元古代镁铁质岩石的岩相学、地球化学和同位素年代学数据。研究发现,这些岩石大致可分为两类多期:(1)年龄较老(ca.940~920Ma)且演化的高Ti岩石(MgO<6.5%,TiO_(2)>2%),负Eu异常明显(Eu/Eu^(*)=0.7~1.0);(2)年龄较年轻(ca.915~890Ma)且较为原始的低Ti岩石(MgO>6.5%,TiO_(2)<2%),具有正Eu异常(Eu/Eu^(*)=1~1.2)或者没有Eu异常(Eu/Eu=1)。早期高Ti岩浆源区类似于EMⅠ型地幔端元(ε_(Nd)(t)=-8~+3),Sr-Nd同位素特征表明其可能是软流圈上涌熔融产生的岩浆与岩石圈地幔相互作用的结果;而晚期低Ti岩石Nd同位素与球粒陨石值类似(ε_(Nd)(t)=-2~+3),可能来源于软流圈地幔。这两类岩石在华北克拉通和巴西圣弗朗西斯科-刚果克拉通几乎同时出现,且可类比。岩浆演化趋势、微量元素和Sr-Nd同位素等特征及单斜辉石-熔体平衡深度计算表明,早期高Ti岩浆产生于大陆岩石圈破裂初期,经历了较高程度的结晶分异作用;而晚期低Ti岩浆的持续作用(~30Myr)可能与岩石圈破裂过程中不断增强的软流圈岩浆活动相关。该裂谷演化进程在Sr同位素特征变化上也有体现,即与早期高Ti岩石相比,晚期低Ti岩石的Sr同位素更为富集但Nd同位素保持不变,表明该类岩石的产生可能在大陆裂谷发育过程中受到海水蚀变的影响。以上证据表明,华北克拉通和巴西圣弗朗西斯科-刚果克拉通在新元古代早期具有可类比的岩石圈应力演化状态,且经历了相似的地幔地球化学动力学过程,支持两个克拉通在该时期相邻。The Early Neoproterozoic(ca.940~890Ma)magmatic event in the North China Craton and S o Francisco-Congo Craton,including dykes,sills and volcanics,were possibly cogenetic and paleo-geographically neighbored based on their coeval ages and close paleomagnetic poles during the Neoproterozoic.The trends in magmatic evolution,mantle source features,and geological processes related to the magmatism are crucial for understanding its genesis and application in continental reconstruction.This study systematically summarizes and analyzes petrological,geochemical,and isotopic data for the Neoproterozoic mafic rocks exposed in the cratons.We found that this sequential magmatism can be roughly divided into two types:(1)the older age group(ca.940~920Ma)includes evolved high Ti rocks(MgO<6.5%,TiO_(2)>2.0%;significant negative Eu anomaly,Eu/Eu^(*)=0.7~1.0);(2)the younger age group(ca.915~890Ma)includes more primitive low Ti rocks with MgO>6.5%,TiO_(2)<2.0%,and either positive Eu anomalies(Eu/Eu^(*)=1.0~1.2)or no Eu anomalies(Eu/Eu=1.0).The mantle source of the early high Ti magmatic component is affinitive to the EMⅠ-type end-member(ε_(Nd)(t)=-8~+3).Geochemical modelling suggests that these features were caused by the interaction between asthenospheric-derived magma and lithospheric mantle.The late low Ti component hasε_(Nd)(t)values near the chondrite values(ε_(Nd)(t)=-2~+3),indicating they were derived from asthenospheric mantle.Both types of magmatism in the North China Craton and S o Francisco-Congo Craton occurred almost simultaneously and can be compared.The characteristics of magma evolution,the features of trace elements and Sr-Nd isotopes,as well as the clinopyroxene-melt equilibrium depth calculation indicate that the early high Ti rocks were generated during the initial rupture of the continental lithosphere and underwent a high degree of crystallization differentiation.The relatively longer magmatic duration of the late low Ti rocks(~30Myr)may be related to the intensified asthenospheric magmatic activity during

关 键 词：华北克拉通 圣弗朗西斯科-刚果克拉通 新元古代 大火成岩省 

分 类 号：P542.4[天文地球—构造地质学] P588.124[天文地球—地质学] P588.145