| 昌宁-孟连缝合带南汀河早古生代埃达克岩锆石U-Pb年龄及其地质意义 |
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| 引用本文： | 吴喆,王保弟,王冬兵,刘函,周放.昌宁-孟连缝合带南汀河早古生代埃达克岩锆石U-Pb年龄及其地质意义[J].地球科学,2020,45(8):3003-3013. |
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| 作者姓名： | 吴喆 王保弟 王冬兵 刘函 周放 |
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| 作者单位： | 1.中国地质科学院, 北京 100037 |
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| 基金项目： | 中国地质调查局项目DD20190053国家自然科学基金项目41773026 |
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| 摘 要： | 前人在昌宁-孟连缝合带获得了大量的晚古生代岩浆活动与沉积地层的记录，但是早古生代的相关记录十分稀少，大大限制了对昌宁-孟连缝合带早古生代演化过程的理解.对南汀河地区早古生代英云闪长岩的锆石U-Pb年龄、全岩地球化学特征开展研究，并探讨其岩石成因，揭示早古生代(原)特提斯演化过程.通过LA-ICPMS锆石U-Pb定年，获得英云闪长岩206Pb/238U加权平均年龄为454.1±2.7 Ma、443.2±2.4 Ma，代表岩浆结晶时代.地球化学分析显示，南汀河英云闪长岩SiO2含量为63.41%~68.57%，K2O含量为1.31%~2.17%，同时具有富Na(Na2O=4.11%~5.07%)贫Mg(MgO=0.98%~1.39%)的特点.REE配分曲线呈现出轻稀土富集、重稀土亏损的特征，大离子亲石元素Sr、Ba等富集，高场强元素Nb、Ta、Ti亏损，与岛弧岩浆的特征相吻合；指示岩浆来源于俯冲板片的部分熔融，在岩浆上升过程中受到了俯冲沉积物的混染，形成于与原特提斯洋俯冲有关的弧火山岩环境，进一步指示早古生代原特提斯洋在454~443 Ma就已经发生了俯冲消减作用.南汀河蛇绿岩与羌塘地区龙木错-双湖缝合带桃形湖等蛇绿岩形成时代一致、地球化学性质相似，由此认为昌宁-孟连缝合带与龙木错-双湖缝合带一起代表了一个统一的古特提斯洋壳的残余.
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| 关 键 词： | 埃达克岩 早古生代 昌宁-孟连缝合带 龙木错-双湖缝合带 特提斯 地球化学 地质年代学 |
| 收稿时间： | 2020-03-23 |
Zircon U-Pb Dating of Early Paleozoic Adakites from Nantinghe Ophiolitic Mélange in Changning-Menglian Suture Zone and Its Geological Implications |
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| Abstract: | A large number of records of magmatic activities and sedimentary strata in the Late Paleozoic have been obtained in the Changning-Menglian suture zone,but the records of Early Paleozoic are very rare,which greatly limits understanding of the Early Paleozoic evolution process in this area. In this paper,the zircon U-Pb age and geochemical characteristics of the Early Paleozoic tonalite are reported in the Nantinghe area,and its petrogenesis is discussed to reveal the evolution process of the Early Paleozoic Tethys. LA-ICPMS zircon U-Pb dating shows that the weighted mean 206Pb/238U ages are 454.1±2.7 Ma and 443.2±2.4 Ma for tonalite,representing the crystallization age of magmatic rocks. Geochemical analyses of the tonalite show that its SiO2 content is 63.41%-68.57% and the K2O content is 1.31%-2.17%,and it is rich in Na (Na2O=4.11%-5.07%) and poor in Mg (MgO=0.98%-1.39%). The REE distribution curve shows the enrichment of LREE and the depletion of HREE,large ion lithophile elements Sr,Ba enrichment,high field strength elements Nb,Ta,Ti depletion,which is consistent with the characteristics of island arc magma,indicating that they were derived from the partial melting of subduction oceanic slab and was contaminated by subduction sediments in the magma rising process,and formed in the arc volcanic environment related to the subduction of the original Tethys ocean,further indicating that the subduction of the proto-Tethys Ocean occurred in 454-443 Ma. The chronology and geochemsitry characteristics of the Nantinghe ophiolite in Changning-Menglian suture zone can be well correlated with the Taoxing Lake ophiolite in the Longmuco-Shuanghu suture zone of Qiangtang area. Thus,it is suggested that both the Changning-Menglian and Longmuco-Shuanghu sutures probably represent the original of a unified paleo-Tethys oceanic crust. |
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