洛南任家滩—荞麦山正长斑岩成因及其对古元古代晚期裂解的指示——岩石化学及锆石U-Pb年龄和Lu—Hf同位素特征  

The genesis of the Renjiatan—Qiaomaishan syenite porphyry in Luonan County and its indication for the late Paleoproterozoic Breakup———Petrochemistry,zircon U-Pb age and Lu—Hf isotope characteristics

作　　者：李毅 李佐臣[1] 赵端昌 赵鹏彬 吕军利 张亚峰 LI Yi;LI Zuochen;ZHAO Duanchang;ZHAO Pengbin;LU Junli;ZHANG Yafeng(School of Earth Science and Resources,Chang’an University,Xi’an,710054;Shaanxi Mineral Geological Survey Center,Xi’an,710068;Shaanxi Institute of Geological Survey,Xi’an,710054)

机构地区：[1]长安大学地球科学与资源学院,西安710054 [2]陕西省矿产地质调查中心,西安710068 [3]陕西省地质调查院,西安710054

出　　处：《地质论评》2024年第1期83-101,共19页Geological Review

基　　金：陕西省公益性地质调查项目“陕西省潼关县幅1∶25万区域地质调查(修测)”(编号:202001);国家自然科学基金资助项目(编号:41872235);中央高校基本科研业务费专项资金项目(编号:300102270202,202110710062,300103183081,300104282717,201810710233);陕西省自然科学基础研究计划项目(编号:2019JM-312);陕西省地质勘查基金项目“陕西小秦岭成矿带石坡地区基础地质调查”(编号:61202110379)的成果。

摘　　要：华北克拉通南缘的陕西洛南—河南豫西地区出露一系列形成于1.8~1.6 Ga的碱性岩,对这些碱性岩的研究有助于提高对华北克拉通南缘古元古代构造环境的认识。笔者等选取陕西省洛南县任家滩—荞麦山一带碱性侵入体进行系统的岩石学、LA-ICP-MS锆石U-Pb年代学、Lu—Hf同位素分析和岩石地球化学研究,讨论了其成因机制和构造背景。研究表明,任家滩—荞麦山岩体的主体岩性为正长斑岩,加权平均年龄为1689±20 Ma(MSWD=0.12),表明其侵位时代为古元古代。该岩体富碱(Na_(2)O+K_(2)O=7.95%~9.5%),高钾(K_(2)O=4.67%~8.51%);稀土元素总量较高(496.15×10^(-6)~650.16×10^(-6),平均543.06×10^(-6)),轻、重稀土元素分馏比较明显,轻稀土元素相对富集(LREE=454×10^(-6)~605×10^(-6)),重稀土元素亏损(HREE=39.3×10^(-6)~45.6×10^(-6)),具有弱负铕异常;K、Rb、Ba、Th富集,Nb、Ta、P、Ti亏损,并且具有明显的Sr负异常。εHf(t)值<0,TDM1值为2038~2218 Ma,TDM2值为2250~2516 Ma,说明岩浆源区物质与富集地幔有关或受到过地壳物质的混染。因此,任家滩—荞麦山岩体是由地幔玄武质岩浆与地壳基底太华杂岩形成的中酸性花岗质岩浆混合后形成的熔体,经强烈的结晶分异作用形成的,其形成于陆内裂谷的构造环境,是华北克拉通南缘对哥伦比亚超大陆裂解事件的响应。Objectives:In the southern margin of North China Craton,a series of alkaline rocks of 1.8~1.6 Ga were found in Luonan,Shaanxi Province,and the west area of Henan Province.The study of these alkaline rocks can facilitate the understanding of the Paleoproterozoic tectonic environment of the southern margin of the North China Craton.Methods:This paper systematically studied the alkaline intrusive rocks in the Renjiatan—Qiaomaishan area in Luonan County,Shaanxi Province in terms of petrology,LA-ICP-MS zircon U-Pb dating,Lu—Hf isotope analysis,and petrogeochemistry,and discussed their genetic mechanism and tectonic setting.Results:The results show that the main lithology of the Renjiatan—Qiaomaishan pluton is syenite porphyry,with a weighted average age of 1689±20 Ma(MSWD=0.12),which indicates that the emplacement of the pluton happened in the Paleoproterozoic.The syenite porphyry is rich in alkali(Na_(2)O+K_(2)O=7.95%~9.5%)and high in potassium(K_(2)O=4.67%~8.51%).The total amount of rare earth elements is high(496.2×10^(-6)~650.2×10^(-6),average 543.1×10^(-6)),and the fractionation of light(LREE=454×10^(-6)~605×10^(-6))and heavy rare earth elements is obvious(HREE=39.3×10^(-6)~45.6×10^(-6)).The light rare earth elements are relatively rich,while the heavy rare earth elements are deficient,and there is a weak negative europium anomaly.In addition,K,Rb,Ba,Th is rich,while Nb,Ta,P,Ti is deficient,and there is an obvious negative Sr anomaly.The value ofεHf(t)is less than 0,the value of TDM 1 is 2038~2218 Ma and TDM2 is 2250~2516 Ma,indicating that the materials in the magmatic source area are related to the enriched mantle or contaminated by the crustal materials.Conclusions:Therefore,the syenite porphyry in the Renjiatan—Qiaomaishan area is a melt formed by mixing the basaltic magma of the mantle with the medium—acid granitic magma formed by the Taihua complex TTG crust.It was formed in the tectonic environment of an intracontinental rift through strong crystallization differentiation,reflecting a re

关 键 词：华北克拉通南缘 碱性侵入体 哥伦比亚超大陆 裂解 

分 类 号：P588.13[天文地球—岩石学] P534.3[天文地球—地质学] P597.3