| 拉萨地体中部古新世早期灯垌火山-侵入杂岩成因及地壳硅质岩浆演化 |
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| 引用本文： | 周逍遥,张玉修,张吉衡,胡俊成,李武毅,黄荣才,廖驾,王家浩,唐显春,朱利东.拉萨地体中部古新世早期灯垌火山-侵入杂岩成因及地壳硅质岩浆演化[J].地球科学,2021,46(2):474-488. |
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| 作者姓名： | 周逍遥 张玉修 张吉衡 胡俊成 李武毅 黄荣才 廖驾 王家浩 唐显春 朱利东 |
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| 作者单位： | 1.中国科学院大学地球与行星科学学院, 北京 100049 |
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| 基金项目： | 中央高校基本科研业务费专项资金;中国地质调查局项目;国家自然科学基金项目 |
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| 摘 要： | 花岗岩-流纹岩的成因研究是认识地壳演化机制的重要途径.通过岩石学、地球化学和同位素地质学方法，对拉萨地体中部措麦地区灯垌破火山机构的火山-侵入杂岩进行了成因研究.灯垌火山-侵入杂岩主要由花岗斑岩、流纹岩和流纹质熔结凝灰岩组成，锆石SHRIMP U-Pb年龄分别为64.1±0.8 Ma、62.9±0.7 Ma和63.2±0.7 Ma，形成时代一致.他们同属高钾钙碱性准铝质-过铝质岩浆岩，亏损高场强元素、富集大离子亲石元素，轻稀土元素富集、重稀土元素平坦，具有一致的锆石δ18O值（6.15‰~7.34‰），为同源岩浆演化的产物.流纹岩与花岗斑岩亏损Ba、Sr、P和Ti元素，具显著的负Eu异常，是岩浆发生不同程度分异演化的产物，前者代表晶粥体分离的熔体相，而后者是晶粥体富矿物相部分的产物.流纹质熔结凝灰岩轻重稀土元素分异程度相对较弱，具中等-弱的Eu负异常，是晶粥体自身被活化喷发的产物.结合前人研究成果，认为灯垌火山-侵入杂岩可能形成于古新世新特提斯洋北向俯冲于拉萨地体之下的过程中，俯冲带流体进入地幔楔并使其部分熔融，形成的幔源物质上涌，使地壳部分熔融形成的中酸性岩浆侵入或喷发而形成侵入岩或火山岩.
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| 关 键 词： | 岩浆演化 复式岩体 锆石U-Pb-O同位素 拉萨地体 地质年代学 地球化学 |
| 收稿时间： | 2019-09-15 |
Petrogenesis of Early Paleocene Dengtong Volcanic-Plutonic Complex in Central Lhasa Terrane and Evolution of Crustal High-Silica Magma |
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| Zhou Xiaoyao,Zhang Yuxiu,Zhang Jiheng,Hu Juncheng,Li Wuyi,Huang Rongcai,Liao Jia,Wang Jiahao,Tang Xianchun,Zhu Lidong.Petrogenesis of Early Paleocene Dengtong Volcanic-Plutonic Complex in Central Lhasa Terrane and Evolution of Crustal High-Silica Magma[J].Earth Science-Journal of China University of Geosciences,2021,46(2):474-488. |
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| Authors: | Zhou Xiaoyao Zhang Yuxiu Zhang Jiheng Hu Juncheng Li Wuyi Huang Rongcai Liao Jia Wang Jiahao Tang Xianchun Zhu Lidong |
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| Affiliation: | (College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;Key Laboratory of Computational Geodynamics,Chinese Academy of Sciences,Beijing 100049,China;Gold Geological Party No.11 of the CAPF,Lhasa 850000,China;Sinoprobe Center,Chinese Academy of Geological Sciences,Beijing 100037,China;Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu 610059,China) |
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| Abstract: | Genetic study on the granite-rhyolite associations is an essential way to uncover the mechanism of crustal evoltion.Geochemistry,zircon U-Pb dating,and oxygen isotopes of the Dengtong volcanic-plutonic complex in the central Lhasa Terrane are reported in this paper.Zircon SHRIMP U-Pb ages for the granite porphyry,rhyolite and rhyolitic ignimbrite samples are 64.1±0.8 Ma,62.9±0.7 Ma and 63.2±0.7 Ma,respectively.These rocks display similar geochemical characterstics.They are high K calc-alkaline and weakly peraluminous,exhibit HFSE depletion,LILE and LREE enrichment,and flat HREE,with consistent zircon oxygen isotopic composition(δ18 O=6.15‰-7.34‰),suggesting consecutive magma evolution of cognate origin.The rhyolite and granite porphyry are depleted in Ba,Sr,P and Ti with significant negative Eu anomaly,indicating conspicuous fractionation.The rhyolite presents the extracted melt from the mush enriched in mineral phases,while the granite porphyry generated from the mush by fractional crystallization.The rhyolitic ignimbrite displays relatively weak negative Eu anomaly,and was generated by the eruption of the residual magma mush.Considering the temporal and spatial distribution of the Paleocene magmatic rocks along the central Lhasa Terrane,it is proposed that the roll-back of the Yarlung-Zangbo Neo-Tethyan oceanic lithosphere subducted beneath the Lhasa Terrane was responsible for the geodynamic regime of the Dengtong volcanic-plutonic complex.The upwelling of the asthenosphere material caused partial melting of lower crust,and resulted in intrusive or volcanic rocks. |
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| Keywords: | magma evolution volcanic-plutonic complex zircon U-Pb-O isotopes Lhasa Terrane geochronology geochemistry |
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