| 藏东南措美大火成岩省中OIB型镁铁质岩的全岩地球化学和锆石Hf同位素 |
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| 引用本文： | 夏瑛,朱弟成,赵志丹,王青,袁四化,陈越,莫宣学.藏东南措美大火成岩省中OIB型镁铁质岩的全岩地球化学和锆石Hf同位素[J].岩石学报,2012,28(5):1588-1602. |
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| 作者姓名： | 夏瑛 朱弟成 赵志丹 王青 袁四化 陈越 莫宣学 |
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| 作者单位： | 1. 地质过程与矿产资源国家重点实验室,中国地质大学地球科学与资源学院,北京100083
2. 防灾科技学院,三河,101601 |
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| 基金项目： | 本文受国家973项目(2012CB822001、2009CB421002)、国家自然科学面上基金项目(40973062、40973026)、国家自然科学重点基金项目(40830317)、中国地质调查局工作项目(1212011121260、1212011121066)、长江学者和创新团队发展计划(IRT1083)及国土资源部公益性行业科研专项(201011054)联合资助. |
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| 摘 要： | 西藏南东部新识别出来的措美大火成岩省的地幔柱头部物质成分尚未得到很好的约束。为探讨此问题,在全岩地球化学数据基础上,本文首次报道了藏东南措美大火成岩省中机布淌、打隆、措美和哲古错OIB型镁铁质岩的锆石Hf同位素和微量元素数据。本文报道的OIB型镁铁质岩包括碱性(组Ⅰ)和亚碱性(组Ⅱ)系列的辉长岩和辉绿岩,以岩墙或岩床的形式产出。这些镁铁质岩具有高的TiO2(2.61%～4.07%)和P2O5(0.32%～0.51%)含量,富集轻稀土元素和高场强元素,地球化学特征类似于OIB。全岩微量元素地球化学指标显示组Ⅰ样品没有或很少受到地壳混染,组Ⅱ样品经历了较高程度的地壳混染。组Ⅰ中一件样品(JBT03-1)具有变化范围大的锆石εHf(t)值(-4.8～+5.3),可能暗示其受到了地壳和/或岩石圈地幔物质的混染。本文结果表明锆石Hf同位素比全岩地球化学数据能够更为有效地识别基性岩浆是否受到地壳和/或岩石圈地幔物质混染。措美大火成岩省中的OIB型镁铁质岩样品(组Ⅰ和组Ⅱ),具有不同于俯冲带镁铁质岩和洋壳镁铁质岩的锆石稀土元素配分型式和锆石Ti温度,这可能是岩浆源区温度和成分不同的结果。综合考虑全岩地球化学和锆石Hf同位素指标,本文提出未受到地壳或岩石圈地幔混染的打隆镇辉长岩体(以组I中的DL01样品为代表)很可能代表了措美大火成岩省纯的地幔柱头部物质成分87Sr/86Sr(t)=0.7047,εNd(t=+1.5,εHf(t=+2.1～+5.7]。这些成分与代表白垩纪Kerguelen地幔柱头部物质的Site 1138和Bunbury Casuarina玄武岩非常相似,可能指示措美大火成岩省中的OIB型镁铁质岩本身就是Kerguelen地幔柱头部物质发生减压熔融的产物。
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| 关 键 词： | 地球化学 锆石Hf同位素 OIB型镁铁质岩 措美大火成岩省 特提斯喜马拉雅带 藏东南 |
| 收稿时间： | 2012/1/12 0:00:00 |
| 修稿时间： | 2012/4/14 0:00:00 |
Whole-rock geochemistry and zircon Hf isotope of the OIB-type mafic rocks from the Comei Large Igneous Province in southeastern Tibet |
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| XIA Ying,ZHU DiCheng,ZHAO ZhiDan,WANG Qing,YUAN SiHu,CHEN Yue and MO XuanXue.Whole-rock geochemistry and zircon Hf isotope of the OIB-type mafic rocks from the Comei Large Igneous Province in southeastern Tibet[J].Acta Petrologica Sinica,2012,28(5):1588-1602. |
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| Authors: | XIA Ying ZHU DiCheng ZHAO ZhiDan WANG Qing YUAN SiHu CHEN Yue and MO XuanXue |
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| Institution: | State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China;State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China;State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China;State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China;Institute of Disaster Prevention, Sanhe 101601, China;State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China;State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China |
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| Abstract: | The plume head composition of the newly recognized Comei Large Igneous Province(LIP) in southeastern Tibet has not yet been well constrained.This paper first reports zircon Hf-isotope and trace elemental data of OIB-type mafic samples from Jibutang,Dalong,Comei and Chigu Tso located within the Comei LIP.These data,combined with the whole-rock geochemical data,are used to explore this issue.The OIB-type mafic rocks reported in this paper include alkaline(Group I) and sub-alkaline(Group II) gabbros and diabases,which outcropped as dikes and sills.These mafic rocks have high TiO2(2.61% ～ 4.07%) and high P2O5(0.32% ～ 0.51%) contents,and are enriched in light rare earth elements(LREEs) and high field strength elements(HFSEs),similar geochemically to Ocean Island basalt(OIB).Geochemical signatures of whole-rock trace element indicate little or no appreciable crustal contamination for Group I samples and significant crustal contamination for Group II samples,respectively.One sample in Group I(JBT03-1) display a wide range of zircon εHf(t) values(-4.8 ～ + 5.3),indicating the involvement of component from crust and/or sub-continental lithospheric mantle.This result suggests that zircon Hf-isotope data can be used as an effective geochemical fingerprint superior to whole-rock geochemistry to determine whether mafic rocks contain components derived from crust and/or subcontinental lithospheric mantle or not.The OIB-type mafic samples in the Comei LIP(Group I and Group II) display distinct zircon rare earth element patterns and Ti-in-zircon temperature from those of mafic rocks from subduction zone and oceanic crust.Such difference is most likely controlled by the different temperature and composition of their magma source regions.Considering the wholerock geochemical and zircon Hf-isotope signatures,this paper proposes that the Dalong gabbroic pluton(represented by sample DL01 in Group I) without contributions from crust and/or sub-continental lithospheric mantle likely represents the pure compositions of plume head of the Comei LIP namely:87Sr/86Sr(t) = 0.7047,εNd(t) = + 1.5,zircon εHf(t) = + 2.1 ～ + 5.7].These compositions are very similar to those of the basalts from Site 1138 and Bunbury Casuarina in SW Australia that were interpreted to represent the Cretaceous Kerguelen plume head materials.This similarity indicates that the OIB-type mafic rocks in the Comei LIP may be the product of decompression melting of the Kerguelen plume head materials. |
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| Keywords: | Geochemistry Zircon Hf isotope OIB-type mafic rocks Comei Large Igneous Province Tethyan Himalaya Southeastern Tibet |
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