内蒙古东乌旗北部早古生代火山岩年代学、地球化学特征及地质意义  

Geochronology,geochemistry and geological significance of Early Paleozoic volcanic rocks in northern East Ujimqin Banner,Inner Mongolia

作　　者：杨泽黎 胡晓佳 王树庆 辛后田 李承东[1] 刘文刚 YANG ZeLi;HU XiaoJia;WANG ShuQing;XIN HouTian;LI ChengDong;LIU WenGang(Tianjin Center of Geological Survey,CGS,Tianjin 300170,China)

机构地区：[1]中国地质调查局天津地质调查中心,天津300170

出　　处：《岩石学报》2020年第4期1107-1126,共20页Acta Petrologica Sinica

基　　金：中国地质调查局地质矿产调查项目(DD20160041)资助.

摘　　要：内蒙古北部二连-东乌旗地区出露早古生代火山岩,为兴蒙造山带北缘构造-岩浆岩带的组成部分,对研究造山带早古生代构造格局及演化具有重要作用。本文对东乌旗北部早古生代中基性及酸性火山岩进行了锆石U-Pb年代学、岩石学、全岩地球化学及Sr-Nd-Hf同位素分析。定年结果显示,中基性火山岩成岩年龄为452±2Ma,酸性火山岩为430±2.0Ma,表明早古生代岩浆活动可延续至中志留世。地球化学组成上,中基性火山岩稀土总量中等,Eu异常不明显,富集Rb、Sr、Th、U等大离子亲石元素,亏损Nb、Ta等高场强元素,特征类似岛弧岩浆岩;酸性火山岩富集Th、U,Eu负异常显著,但Rb、Ba等大离子亲石元素富集程度不高,Nb、Ta等高场强元素亏损不明显,表现出板内岩浆特点。中基性和酸性火山岩均具有亏损的同位素组成:中基性火山岩εNd(t)=+2.03^+2.67,εHf(t)值介于+7.9^+14.5之间;酸性火山岩εNd(t)=+4.94,εHf(t)值为+9.9^+15.3。岩石学及地球化学分析表明,中基性火山岩为岛弧环境下遭受俯冲流体交代的地幔楔部分熔融产物,酸性火山岩则来源于新生基性下地壳熔融并具有板内岩浆特征,可能指示了俯冲的结束。结合前人资料,二连-东乌旗地区早古生代岩浆活动介于晚寒武-中志留世之间,形成时间及阶段性演化特征近似于苏尼特左旗-锡林浩特早古生代岩浆岩带,暗示两者可能具有成因联系,均为早古生代古亚洲洋向北俯冲的产物。Early Paleozoic volcanic rocks are outcropped in the Erenhot-East Ujimqin Banner area of northern Inner Mongolia,and taken for part of the Paleozoic tectonic-magmatic belt of northern Xing-Meng Orogenic Belt(XMOB).However,little attention has been paid on these volcanic rocks in previous works.In this study,we present petrological investigations as well as geochronological,geochemical and Sr-Nd-Hf isotopic data for the volcanic rocks in northern East Ujimqin Banner,to reveal their petrogenesis and envisage the Early Paleozoic tectonic evolution of XMOB.Volcanic rocks could be classified into basic-intermediate and felsic sort.Zircon LA-ICP-MS U-Pb dating indicates the basic-intermediate volcanic rocks erupted 452±2Ma ago and the felsic volcanic rocks yields a weighted mean age of 430±2Ma,indicating that the Early Paleozoic magmatic activity may extend to the Middle Silurian.Geochemically,the basic-intermediate volcanic rocks are generally enriched in LILE and LREE,depleted in HFSE,without obvious Eu anomalies,which is similar to the island arc or active continental margin magmatite.The felsic volcanic rocks display the characteristics of within-plate magmatism,with enrichment of Th,U,depletion of HFSE(e.g.,Nb,Ta),and not obvious enriched in LILE(e.g.,Rb,Sr).All the volcanic rocks show depleted isotopic composition:εNd(t)values of basic-intermediate and felsic volcanic rocks are+2.03^+2.67 and+4.94 respectively,andεHf(t)values of those varying from+7.9^+14.5 and+9.9^+15.3.Taking all the data into consideration,we suggest that the Late Ordovician intermediate-basic volcanic rocks were generated in island arc setting and formed by partial melting of a mantle wedge metasomatized by subducted slab derived fluids,while the felsic volcanic rocks were derived from juvenile basic lower crust and with features of within-plate granite.Combined with previous studies,our research demonstrates that the formation time and magmatic evolution characteristics of Early Paleozoic igneous rocks in Erenhot-East Ujimqin Banner area

关 键 词：火山岩 早古生代 兴蒙造山带 古亚洲洋 构造-岩浆演化 

分 类 号：P588.14[天文地球—岩石学] P597.3[天文地球—地质学]