内蒙古集宁地区徐武家变质辉长岩的形成背景及其地质意义  

Tectonic setting and geological significance of Xuwujia metagabbro in Jining area,Inner Mongolia

作　　者：王智 王惠初 施建荣 常青松 张家辉 任云伟 相振群[3,4] WANG Zhi;WANG Hui-chu;SHI Jian-rong;CHANG Qing-song;ZHANG Jia-hui;REN Yun-wei;XIANG Zhen-qun(China Mining News,Beijing 100037,China;International Mining Research Center,China Geological Survey,Beijing 100037,China;Tianjin Centre,China Geological Survey,Tianjin 300170,China;Precambrain Geological Research Centre,China Geological Survey,Tianjin 300170,China)

机构地区：[1]中国矿业报社,北京100037 [2]中国地质调查局国际矿业研究中心,北京100037 [3]中国地质调查局天津地质调查中心,天津300170 [4]中国地质调查局前寒武纪地质研究中心,天津300170

出　　处：《地质调查与研究》2020年第2期97-113,共17页Geological Survey and Research

基　　金：中国地质调查局地调项目“燕山-太行成矿带丰宁和天镇地区地质矿产调查(DD20160042)”;“河北怀安-内蒙古凉城地区区域地质调查(DD20190035)”;“全球矿业大数据挖掘集成与智能决策服务平台建设(DD20201181)”;国家自然科学青年基金项目“天镇地区与孔兹岩系共生的“MORB”型高压基性麻粒岩成因研究(41902196)”;“阿拉善地块东缘叠布斯格地区高压基性麻粒岩的变质作用P-T-t轨迹研究(41602199)”。

摘　　要：徐武家变质辉长岩出露于内蒙古集宁土贵乌拉地区,侵入在孔兹岩系中,与孔兹岩系的超高温变质作用和深熔作用存在密切的成因联系。本文在区域地质填图基础上,对徐武家辉长岩开展了岩石学、岩石地球化学和同位素年代学等研究。徐武家辉长岩属偏碱性中基性岩,钾钠含量变化大。岩石富集稀土,轻、重稀土分馏强烈,显弱负铕异常。微量元素表现大离子亲石元素Rb、Ba、K、Sr、Pb富集,高场强元素Th、U、Nb、Ta、Ti明显亏损。从变质辉长岩中获得了1917±12 Ma的岩浆结晶年龄和1910±26 Ma、1915±11 Ma的变质年龄。锆石Hf同位素测试显示εHf(t)多为负值,Hf模式年龄(TDM)为2273~2501 Ma。综合研究表明徐武家辉长岩可能来源于富集地幔,在上升过程中遭受了地壳物质的混染,并在就位后遭受了麻粒岩相变质作用和富钾质流体的交代。辉长岩就位于下地壳,表明在其侵位之前孔兹岩系已处于地壳深部。结合怀安地块上高压麻粒岩的形成年龄(1.95~1.93 Ga),集宁孔兹岩系原岩沉积时代应早于1.95 Ga。徐武家变质辉长岩应形成于古元古代陆-陆碰撞造山过程中由挤压背景向伸展背景的转换阶段,是碰撞造山峰期俯冲板片断离、幔源岩浆上涌侵位的产物,对造山峰期的时限有重要制约作用。The Xuwujia metagabbro exposed in Tuguiwula area,Jining,Inner Mongolia,intruded into khondalite occur as small plutons and is believed to be closely related to the ultrahigh-temperature metamorphism and anatexis of the khondalite.Based on the regional geological mapping,this paper focuses on the characteristic of petrology,petrochemistry and isotopic geochronology of the Xuwujia metagabbro.The metagabbro belongs to alkaline series rock,with SiO2 content of 48.58%~55.25%,and the content of potassium and sodium varies greatly(K2O/Na2O of 0.33~1.68).It is characterized by enriched rare earth elements,strong fractionation between light and heavy rare earth elements with a weak negative Eu anomaly and enrichment of large ion lithophile elements Rb,Ba,K,Sr and Pb,and evident depletion of the high field strength elements Th,U,Nb,Ta and Ti.The magmatic crystallization age of 1917±12 Ma and the metamorphic ages of 1910±26 Ma and 1915±11 Ma were obtained from the metagabbro.The test result of zircon Hf isotope shows thatεHf(t)is mostly negative with a single-stage Hf model age(TDM)in the range of 2273~2501 Ma.It is suggested that the Xuwujia gabbro may originate from the enriched mantle source,which was contaminated by crustal materials during the ascending process,and subsequently suffered granulite facies metamorphism and potassium rich fluid metasomatism.The gabbro emplaced in lower crust,which means that the khondalite has entered the lower crust before emplacement of the gabbro.According to the 1.95~1.93 Ga metamorphic age of the high-pressure granulite in the Huai'an block,it can be inferred that the protolith sedimentary age of the khondalite in Jining should be earlier than 1.95 Ga.It can be concluded that the Xuwujia metagabbro was formed in the transition stage from compression to extension during Paleoproterozoic collision orogeny.It is the product of subduction slab-breakoff,lithosphere delamination and upwelling emplacement of mantle derived magma,and has an important constraints on the time of collision o

关 键 词：变质辉长岩 孔兹岩系 古元古代 构造背景 集宁地区 华北克拉通 

分 类 号：P534.52[天文地球—古生物学与地层学] P588.311[天文地球—地质学]