后马场镁铁-超镁铁岩体岩石成因及其对华北克拉通破坏的指示意义  

Petrogenesis of the Houmachang Mafic-ultramafic Intrusion and Its Implications for the Destruction of the North China Craton

作　　者：张飞飞 邓宇峰[1,2,3] 袁峰 张儒林[1,2,3] 王乐乐 逯登栋 李卫东 ZHANG Feifei;DENG Yufeng;YUAN Feng;ZHANG Rulin;WANG Lele;LU Dengdong;LI Weidong(School of Resources and Environmental Engineering,Hefei University of Technology,Hefei 230009,Anhui,China;Anhui Provincial Key Laboratory for Deep Exploration,Evaluation and Utilization of Strategic Mineral Resources,Hefei 230009,Anhui,China;Anhui Province Engineering Research Center for Mineral Resources and Mine Environments,Hefei 230009,Anhui,China;Geological Tam 325 of Anhui Provincial Bureau of Geology and Mineral Exploration,Huaibei 235000,Anhui,China;Qinghai Yellow River Mining Co.,Ltd.,Golmud 816000,Qinghai,China;No.6 Geological Team,Xinjiang Bureau of Geology and Exploration,Hami 839000,Xinjiang,China)

机构地区：[1]合肥工业大学资源与环境工程学院,安徽合肥230009 [2]安徽省战略性矿产资源深部探测与评价利用重点实验室,安徽合肥230009 [3]安徽省矿产资源与矿山环境工程技术研究中心,安徽合肥230009 [4]安徽省地质矿产勘查局三二五地质队,安徽淮北235000 [5]青海黄河矿业有限责任公司,青海格尔木816000 [6]新疆地质矿产勘查开发局第六地质大队,新疆哈密839000

出　　处：《大地构造与成矿学》2024年第5期1128-1147,I0017,I0018,共22页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(42272083,U1803113);第二次青藏高原综合科学考察研究项目(2019QZKK0708);安徽省公益性地质工作项目(2021-g-2-9,2021-g-2-11)联合资助。

摘　　要：文本通过对华北克拉通东南缘徐宿弧地区后马场镁铁质?超镁铁质岩体进行岩相学、锆石U-Pb年代学、单斜辉石和橄榄石矿物成分、全岩地球化学以及锆石Hf同位素研究,确定该岩体的形成时代、岩石成因及其构造环境,探究华北克拉通深部地幔性质及其演化过程。后马场岩体主要由辉长岩、橄长岩和橄榄辉长岩组成,其中辉长岩LA-ICP-MS锆石U-Pb年龄为109±2 Ma,指示该岩体形成于早白垩世晚期。不同岩性岩石的Si_(2)、CaO、Al_(2)O_(3)、Ti_(2)、Na_(2)O+K_(2)O与MgO呈明显的规律性变化,具有相似的主量元素特征,说明其为同源岩浆演化的产物。后马场岩体相对富集大离子亲石元素(Rb、Ba、Sr),亏损高场强元素(Nb、Ta、Zr、Hf、Ti),具有典型的岛弧型岩浆特征。辉长岩中锆石的ε_(Hf)(t)值为–14.5~5.6,大部分为负值,说明岩浆源区以富集地幔占主导,同时也具有亏损地幔的特征。微量元素Nb/U-Ce/Pb模拟计算结果显示,岩浆发生了80%~90%的上地壳混染,然而岩浆无法同化混染如此高比例的上地壳物质,因此部分地壳物质可能是通过陆壳俯冲并进行源区交代作用进入岩浆。岩石的La/Ba、Th/Yb值与俯冲交代岩石圈地幔相似,Nb/Zr、Th/Zr、Rb/Y和Nb/Y值显示俯冲熔体交代的特征,指示俯冲扬子陆壳衍生熔体交代了岩石圈地幔,在白垩纪古太平洋俯冲板片回卷,岩石圈地幔受到上涌的软流圈地幔的加热,产生的镁铁质岩浆形成了后马场岩体。区域镁铁质岩石锆石ε_(Hf)(t)值的变化规律指示后马场岩体侵位时期是华北克拉通东南缘地幔源区由富集地幔向亏损地幔转折的关键期,在此之后,镁体质岩浆主要源于亏损地幔,因此华北克拉通东南缘早白垩世晚期镁铁质岩浆指示岩石圈地幔源区性质由富集向亏损转变的结束,也代表着华北克拉通破坏的结束。Based on petrography,zircon U-Pb chronology and Hf isotope analyses,the compositions of clinopyroxene and olivine,whole-rock geochemistry of the Houmachang mafic-ultramafic intrusion in the Xusuhu area along the southeast margin of the North China Craton,the petrogenesis and tectonic environment of the intrusion were studied to explore the mantle evolution process beneath the North China Craton.The Houmachang intrusion is mainly composed of gabbro,troilite,and olivine gabbro.The gabbro LA-ICP-MS zircon U-Pb age is 109±2 Ma,indicating that the intrusion was formed in the late Early Cretaceous.The coordinated variation between Si_(2),CaO,Al_(2)O_(3),TiO_(2),Na_(2)O+K_(2)O,and MgO,the similar major element distribution patterns for the different types of intrusive rocks,suggest that they are related to each other by differentiation of the same primary magma.The Houmachang intrusive rocks are enriched in large-ion lithophile elements(Rb,Ba,and Sr)and depleted in high-field strength elements(Nb,Ta,Zr,Hf,and Ti)relative to mid-ocean ridge basalt,similar to those of typical island arc basalts.The zirconε_(Hf)(t)values of the gabbros range from-14.5 to 5.6,most of which are negative,indicating that the mantle source of the intrusive rocks was dominantly enriched mantle.The simulation calculation results for the Nb/U and Ce/Pb ratios showed that the parental magma of the Houmachang intrusive rocks could have experienced 80%-90%contamination with the upper crust,but the magma could not contaminate such a high proportion of the upper crust material.Therefore,some of crust material may have entered the magma through subduction of the continental crust and metasomatism in the source region.The La/Ba and Th/Yb ratios are similar to those of the metasomatic lithospheric mantle.The Nb/Zr,Th/Zr,Rb/Y,and Nb/Y ratios of the Houmachang rocks are similar to those of basalts derived from melt-metasomatized mantle,indicating that their primary magma was generated by partial melting of the lithospheric mantle metasomatized by subducte

关 键 词：华北克拉通东南缘 镁铁-超镁铁质岩 地球化学特征 锆石U-Pb年龄 HF同位素 俯冲交代岩石圈地幔 

分 类 号：P581[天文地球—岩石学] P595[天文地球—地质学]