今天是2019年07月23日

内蒙古狼山北部早古生代岩浆岩年代学、地球化学特征及构造意义

DOI:10.3799/dqkx.2018.305

作者:张云,孙立新,张天福,滕 飞,张永,孙义伟,杨泽黎,许凡

联系地址:中国地质调查局天津地质调查中心,天津 300170

摘要:内蒙古狼山北部地区位于华北克拉通与兴蒙造山带交接部位,构造上隶属于华北克拉通北缘早古生代陆缘增生带.狼山北部巴音杭盖一带出露的早古生代岩浆岩,对确定华北北缘西段早古生代构造格局和造山带演化具有重要意义.本次研究采用LA-MC-ICP-MS锆石U-Pb测年法,获得了闪长岩、石英闪长岩206Pb/238U年龄为435.8±2.2 Ma~437.7±2.2 Ma,时代为早志留世.岩石为钙碱性系列,富集轻稀土元素,(La/Yb)N=4.30~11.59,表现出不同程度地富集大离子亲石元素(LILE)Rb、Th、U、K、Ba、Sr等,亏损高场强元素(HFSE),具有明显的Nb、Ta、Ti负异常,具有弱的负Eu异常(δEu=0.80~0.96),具有俯冲带岩石的特征.在同位素组成上,早志留世闪长岩体具有明显亏损的特点,εHf(t)=+5.2~+12.6,(87Sr/86Sr)i= 0.704 665 ~0.706 174,εNd(t)=+1.84~+2.00.上述年代学、岩石地球化学、SrNdHf同位素数据结合区域地质资料分析表明,狼山北部早志留世闪长质岩体形成于早古生代温都尔庙洋沿温都尔庙-乌德-索伦山南一线南向俯冲背景下,为经历了俯冲洋板片析出流体交代作用的新生下地壳部分熔融的产物.志留纪岛弧岩浆岩的确定,明确了狼山北部地区属于华北克拉通北缘早古生代活动大陆边缘,为白乃庙岛弧带向西延展的部分,同时为华北北缘西段早古生代“沟-弧-盆”体系的确定提供了重要素材.

关键字:早古生代;锆石U-Pb年代学;地球化学;Sr-Nd-Hf同位素;岛弧岩浆岩;内蒙古狼山北部.

Geochronology, Geochemistry and its Tectonic Significance of the Early Paleozoic Magmatic Rocks in Northern Langshan, Inner Mongolia

Author:Zhang Yun , Sun Lixin , Zhang Tianfu , Teng Fei , Zhang Yong , Sun Yiwei , Yang Zeli , Xu Fan

Author Address:Tianjin Center of China Geological Survey, Tianjin 300170, China

Abstract:The Langshan area in Inner Mongolia is a paramount transitional zone located between the North China Craton (NCC) and the Xingmeng orogenic belt (XOB), and structurally belongs to the Early Paleozoic marginal accretionary belt in the northern margin of the NCC. The Early Paleozoic magmatic rocks distributed in the Bayinhangai area, the northern Langshan, have important implications for the reconstruction of regional Paleozoic tectonic setting and orogenic evolution. The dioritic batholith consists mainly of diorite and quartz-diorite, with the zircon 206Pb/238U ages of 435.8±2.2 Ma-437.7±2.2 Ma, which represent the crystallization age of the Early Silurian. The rocks are calc-alkaline series, enriched in LREE with the (La/Yb)N ratios 4.30~11.59, depleted in HFSE (especially Nb, Ta and Ti) and enriched in LILE (like Rb, Th, K, Ba and Sr), and weakly negative Eu anomalies (δEu=0.80~0.96), indicating that they are formed in island arcs or in active continents margin setting. The Early Silurian diorite batholith shows depleted isotopic compositions, εHf(t)=+5.2-+12.6, (87Sr/86Sr)i=0.704 665-0.706 174,εNd(t)=+1.84-+2.00. Integrated geochronology, geochemical, Sr-Nd-Hf isotopic data and regional geological data suggest that the Early Silurian diorite batholith in northern Langshan was generated in Early Paleozoic and resulted from the southward subduction of Wenduermiao Ocean along Wenduermiao-Wude-northern Suolun. The diorites were formed by partial melting of juvenile crust which was modified by subduction slab fluids. The determination of the Silurian arc magmatic rocks makes it clear that the northern Langshan area belongs to the Early Paleozoic active continental margin of the northern NCC, and it is the westward extended part of the Bainaimiao island arc belt. At the same time, it also provides important materials for the Early Paleozoic “trencharcbasin” system in the west section of the northern NCC.

Keyword:Early Paleozoic; zircon U-Pb geochronology; geochemistry; Sr-Nd-Hf isotopic compositions; arc magmatic rocks; northern Langshan, Inner Mongolia.

 

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作者简介:张云(1991-),男,助理研究员,硕士,从事构造地质学和区域地质研究.ORCID: 0000-0002-1948-1284. E-mail: 571938243@qq.com

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