| 内蒙古狼山地区乌花辉长岩的年代学、地球化学和Sr-Nd-Hf同位素组成:对地幔源区特征和岩石成因的约束 |
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| 引用本文： | 张云,孙立新,张天福,孙义伟,张祺,李艳锋,杨泽黎,刘文刚.内蒙古狼山地区乌花辉长岩的年代学、地球化学和Sr-Nd-Hf同位素组成:对地幔源区特征和岩石成因的约束[J].现代地质,2020,34(3):450-465. |
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| 作者姓名： | 张云 孙立新 张天福 孙义伟 张祺 李艳锋 杨泽黎 刘文刚 |
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| 作者单位： | 1.中国地质调查局 天津地质调查中心,天津 3001702.华北地质科技创新中心,天津 300170 |
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| 基金项目： | 国家自然科学基金项目(41572172);中国地质调查局项目(DD20189615);中国地质调查局项目(DD20160041) |
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| 摘 要： | 内蒙古狼山地区乌花辉长岩体主要由橄榄辉长岩和角闪辉长岩组成,其锆石LA-ICP-MS U-Pb同位素测年结果表明,岩体形成于(319.8±1.8)325.4±1.6 Ma,属于早石炭世末期岩浆活动的产物。地球化学特征上,乌花辉长岩属低钾钙碱性玄武岩系列,具有较高的Mg#(多在76.70~80.35之间)、Al2O3(13.55%~25.13%)和较低的TiO2(0.18%~1.35%)。稀土总含量较低(∑REE=8.92×10^-6~40.10×10^-6),稀土元素分馏程度不高,呈现出轻稀土元素(LREE)略微富集、重稀土元素(HREE)相对亏损((La/Yb)N =1.74~3.06)的特点,Eu呈明显的正异常(δEu=1.156~3.86)。岩石富集Pb和K、Rb、Ba、Sr等大离子亲石元素,明显亏损Nb、Ta、Zr、Hf、Th等高场强元素,较低的Zr含量(4.38×10^-6~26.6×10^-6)和Zr/Y比值(1.08~2.35),呈现出典型的俯冲-消减带弧火山岩的地球化学特征。Sr-Nd-Hf同位素研究表明,乌花辉长岩岩浆源区为富集地幔,在侵位过程中受到的地壳混染程度较弱。结合区域地质背景,认为乌花辉长岩为俯冲-消减构造体制下由俯冲带流体交代富集地幔部分熔融而成,代表了俯冲相对早期阶段的产物,指示华北板块北缘西段在早石炭世晚期开始进入到安第斯型活动大陆边缘阶段,并可能结束于早二叠世之前。
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| 关 键 词： | 辉长岩 锆石U-PB年代学 地球化学 SR-ND-HF同位素 安第斯型活动大陆边缘 内蒙古狼山地区 |
| 收稿时间： | 2018-11-02 |
| 修稿时间： | 2019-12-11 |
Geochronology,Geochemistry and Sr-Nd-Hf Isotopic Compositions of the Wuhua Gabbros in Langshan,Inner Mongolia: Constraints for Mantle Sources and Petrogenesis |
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| ZHANG Yun,SUN Lixin,ZHANG Tianfu,SUN Yiwei,ZHANG Qi,LI Yanfeng,YANG Zeli,LIU Wengang.Geochronology,Geochemistry and Sr-Nd-Hf Isotopic Compositions of the Wuhua Gabbros in Langshan,Inner Mongolia: Constraints for Mantle Sources and Petrogenesis[J].Geoscience——Journal of Graduate School,China University of Geosciences,2020,34(3):450-465. |
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| Authors: | ZHANG Yun SUN Lixin ZHANG Tianfu SUN Yiwei ZHANG Qi LI Yanfeng YANG Zeli LIU Wengang |
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| Institution: | 1. Tianjin Center of Geological Survey, China Geological Survey, Tianjin 300170, China2. North China Center for Geoscience Innovation, Tianjin 300170, China |
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| Abstract: | Two types of gabbros (i.e., olivine and hornblende gabbros) are exposed in the Wuhua gabbroic intrusions. LA-ICP-MS zircon U-Pb dating indicates that the Wuhua gabbros were emplaced in the late Early Carboniferous ((319.8±1.8) Ma to (325.4±1.6) Ma). The Wuhua gabbros are tholeiitic, with high Mg# va-lues (mostly 76.70-80.35), high Al2O3 (13.55%-25.13%) and low TiO2 (0.18%-1.35%). The rocks have low total REE contents (∑REE=8.92×10-6-40.10×10-6), and are featured by LREE enrichments ((La/Yb)N=1.74-3.06) and positive Eu anomaly (δEu=1.156-3.86). The Pb and LILE (K, Rb, Ba, Sr) enrichments and HFSE (Nb, Ta, Zr, Hf, Th) depletions, and the relatively low Zr content (4.38×10-6-26.6×10-6) and low Zr/Y ratio (1.08-2.35) resemble those of typical subduction-related arc volcanic rocks. The Sr-Nd-Hf isotopic data show that the Wuhua gabbros were derived from an enriched mantle source, and that crustal assimilation was likely insignificant. According to geochemical data and previous regional geological studies, we consider that the Wuhua gabbros may have formed from partial melting of the hydrated and enriched lithospheric mantle wedge. The Wuhua gabbros were likely formed in the incipient subduction phase, when the western section of the northern North China Plate margin started to become an Andean-type continental arc in the late Early Carboniferous. This tectonic phase may have ended before the Early Permian. |
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| Keywords: | gabbro zircon U-Pb geochronology geochemistry Sr-Nd-Hf isotope Andean-type active continental margin Langshan Inner Mongolia |
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