| 内蒙古拜仁达坝石炭纪岩体年代学、地球化学、Sr-Nd同位素特征及其对中亚造山带的制约 |
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| 引用本文： | 张艳飞,周永恒,董洋,李琛,王刚.内蒙古拜仁达坝石炭纪岩体年代学、地球化学、Sr-Nd同位素特征及其对中亚造山带的制约[J].地球科学,2022,47(4):1234-1252. |
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| 作者姓名： | 张艳飞 周永恒 董洋 李琛 王刚 |
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| 作者单位： | 1.中国地质调查局沈阳地质调查中心，辽宁沈阳 110034 |
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| 基金项目： | 中国地质调查局项目(No.DD20190438)； |
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| 摘 要： | 为探讨内蒙古拜仁达坝岩体岩浆来源与构造环境，进而限制古亚洲洋闭合时间，锆石U-Pb年代学、岩石地球化学及Sr-Nd同位素地球化学研究结果表明，岩体由花岗闪长岩和石英闪长岩组成，岩石侵位年龄为327±2 Ma（MSWD=1.4）. 岩体具有偏铝质-弱过铝质钙碱性特征，富集Rb、Th、U、K，亏损Ba、Sr、P及Nb、Ta、Ti等高场强元素，Eu负异常，具典型岛弧钙碱性Ⅰ型花岗岩特征. 岩体具有亏损的Sr-Nd同位素组成，（87Sr/86Sr）i=0.705 8~0.709 6，εNd（t）=-4.93~0.01，TDM2=1.08~1.48 Ga，且锆石中发现有继承锆石，高Rb/Sr（0.70~2.63）、Zr/Hf（35.88~77.17）比值，表明岩浆起源于早石炭世晚期由中元古代幔源基性地壳物质熔融.拜仁达坝岩体形成于俯冲带的活动大陆边缘环境，认为西伯利亚板块南缘在晚石炭世已进入俯冲消减的活动大陆边缘演化阶段，进而表明此时古亚洲洋俯冲作用仍在持续.对兴蒙造山带南部早中二叠世中酸性岩体的研究也得到同样的结论，表明晚石炭世到晚二叠世古亚洲洋一直在向北俯冲消减，直到中晚三叠世后造山伸展环境形成的花岗岩类岩体出现，暗示古亚洲洋完全闭合.
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| 关 键 词： | 拜仁达坝岩体 Sr-Nd同位素 古亚洲洋 活动大陆边缘 岩石学 |
| 收稿时间： | 2021-01-15 |
Geochronological,Geochemical and Sr-Nd Isotopic Characteristics of Carboniferous Rock Mass in Bayern Daba Area,Inner Mongolia and Its Constraints on Central Asian Orogenic Belt |
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| Zhang Yanfei,Zhou Yongheng,Dong Yang,Li Chen,Wang Gang.Geochronological,Geochemical and Sr-Nd Isotopic Characteristics of Carboniferous Rock Mass in Bayern Daba Area,Inner Mongolia and Its Constraints on Central Asian Orogenic Belt[J].Earth Science-Journal of China University of Geosciences,2022,47(4):1234-1252. |
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| Authors: | Zhang Yanfei Zhou Yongheng Dong Yang Li Chen Wang Gang |
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| Abstract: | In order to examine the magma origin and tectonic setting of the Bayern Daba rock mass in Inner Mongolia and thereby limit the closure of the paleo-Asian Ocean, zircon LA-ICP-MS U-Pb geochronological, geochemical and Sr-Nd isotopic measurement and analysis are presented in this paper. Zircon U-Pb dating yields a weighted mean age of 327±2 Ma(MSWD=1.4), indicating an Early Carboniferous magmatic event. The Bayern Daba rock mass is characterized by the high Si, Na, Mg, Fe and metaluminous-peraluminous features. They are relatively enriched in Rb, Th, U and K, depleted in Ba, Sr, P, Nb, Ta and Ti, and enriched in LREE over HREE with negative Eu anormaly, showing the calc-alkaline Ⅰ-type granite in island arc. Their depleted isotopic compositions with (87Sr/86Sr)i from 0.705 8 to 0.709 6, negative εNd(t) values from -4.93 to 0.01, and TDM2 from 1.08 to 1.48 Ga, as well as the inherited zircon present in zircon, indicating that the magma source was derived from the partial melting of Mesoproterozoic mantle-derived basic materials. High Rb/Sr (0.70-2.63) and Zr/Hf (35.88-77.17) ratios and the positive correlation of ISr and εNd(t) isotopic data suggest contamination by a proportion of mantle material. Combined with regional tectonic evolution, the Bayern Daba rock mass was formed in the island-arc environment of an active continental margin in Carboniferous, which further suggests that the subduction of the paleo-Asian Ocean was still ongoing at that time. The same conclusion is also reported about the Early Permian intermediate-acidic rock masses in the southern part of the Xing-Meng orogenic belt, suggesting that the paleo-Asian Ocean had been subducting northward from Late Carboniferous up to Late Permian and did not fully close until the appearance of granitoids formed in a post-orogenic extensional environment in Middle to Late Triassic. |
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