| 胶-辽-吉活动带中段古元古代早期构造演化:来自牧牛河和大房身岩体的证据 |
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| 引用本文： | 陈志刚,朱凯,刘杰勋,李文庆.胶-辽-吉活动带中段古元古代早期构造演化:来自牧牛河和大房身岩体的证据[J].地球科学,2021,46(5):1710-1727. |
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| 作者姓名： | 陈志刚 朱凯 刘杰勋 李文庆 |
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| 作者单位： | 自然资源部机关服务局,北京 100812;吉林大学地球探测科学与技术学院,吉林长春 130061;长春工程学院勘查与测绘工程学院,吉林长春 130021;自然资源部东北亚矿产资源评价重点实验室,吉林长春 130061 |
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| 基金项目： | 国家自然科学基金项目41272223中国地质调查局项目1212011220247自然资源部东北亚矿产资源评价重点实验室自主基金课题项目DBY-ZZ-19-22 |
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| 摘 要： | 辽吉花岗岩是胶-辽-吉活动带的重要组成部分，它们是限定胶-辽-吉活动带早期构造属性的重要依据.由于辽吉花岗岩的属性一直存在争议，所以胶-辽-吉带的早期构造环境也一直没有定论.通过对牧牛河-大房身地区的辽吉花岗岩（牧牛河岩体和大房身岩体）进行年代学和地球化学分析，以探讨该地区辽吉花岗岩成因和地质意义.锆石U-Pb定年结果表明，牧牛河岩体和大房身岩体分别形成于2 176±4 Ma和2 179±4 Ma.牧牛河花岗岩和大房身花岗岩具有相似的岩石地球化学特征，它们都富SiO2（72.85%~77.67%），富碱（K2O+Na2O=7.65%~8.86%），贫Ca、Mg、Al（CaO=0.10%~0.92%，MgO=0.03%~0.09%，Al2O3=11.49%~12.67%），且K2O/Na2O值较高（0.99~1.83）.牧牛河花岗岩和大房身花岗岩的稀土配分模式曲线都为右倾型，有较强的负Eu异常（Eu/Eu*=0.08~0.56）和较高的Ga/Al比值，而且岩体富集Zr、U、Y等高场强元素以及Rb、K等大离子亲石元素，贫Ba、Sr等元素.锆石饱和温度计算表明牧牛河花岗岩（855~871 ℃）和大房身花岗岩（850~886 ℃）都属于高温花岗岩.较低的Nb/Y比值和较高的岩浆温度暗示牧牛河花岗岩和大房身花岗岩为A2型花岗岩，主要来源于减薄的下地壳岩石的部分熔融.大量A2型辽吉花岗岩的出现，再结合活动带内最近发现的钠质辽吉花岗岩和钙碱性中基性岩，表明胶-辽-吉活动带早期的构造环境为弧后盆地.
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| 关 键 词： | 胶-辽-吉活动带 辽吉花岗岩 A2型花岗岩 弧后盆地 构造地质学 |
| 收稿时间： | 2020-07-10 |
Early Paleoproterozoic Tectonic Evolution of Central Jiao-Liao-Ji Belt:Evidence from Muniuhe and Dafangshen Plutons |
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| Chen Zhigang,Zhu Kai,Liu Jiexun,Li Wenqing.Early Paleoproterozoic Tectonic Evolution of Central Jiao-Liao-Ji Belt:Evidence from Muniuhe and Dafangshen Plutons[J].Earth Science-Journal of China University of Geosciences,2021,46(5):1710-1727. |
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| Authors: | Chen Zhigang Zhu Kai Liu Jiexun Li Wenqing |
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| Abstract: | Liaoji granitoids are important constituents of the Jiao-Liao-Ji belt (JLJB), and they provide important constraints on tectonic setting of the JLJB. The tectonic setting of the JLJB is still controversial due to the debate on nature of the Liaoji granitoids. It conducted zircon U-Pb geochronological and geochemical analyses of Liaoji granitoids (Muniuhe and Dafangshen plutons) in the Muniuhe-Dafangshen area, and then discuss the petrogenesis and geological significance of these granitoids. LA-ICP-MS U-Pb zircon dating gives the emplacement age of 2 176±4 Ma and 2 179±4 Ma for Muniuhe and Dafangshen plutons, respectively. Muniuhe and Dafangshen granitoids display similar geochemical characteristics. They have high SiO2 (72.85%-77.67%), alkalis (K2O+Na2O=7.65%-8.86%) and K2O/Na2O ratios (0.99-1.83), and low CaO (0.10%-0.92%), MgO (0.03%-0.09%) and Al2O3 (11.49%-12.67%) contents. The chondrite-normalized REE patterns of Muniuhe and Dafangshen granitoids show right-dipping linear trends with slightly negative Eu anomalies (Eu/Eu*=0.08-0.56) and high Ga/Al ratios. They are enriched in high field strength elements (HFSEs; e.g., Zr, U and Y) and large-ion lithophile elements (LILEs; e.g., Rb and K), and depleted in Nb, P, Ti and Sr. In addition, they display high Zr saturation temperatures (855-871 ℃ and 850-886 ℃, repectively). Low Nb/Y ratios and high Zr saturation temperatures indicate that the Muniuhe and Dafangshen granitoids have affinities with A2-subtype granitoids, and they were derived from thinned lower crust. The occurrence of voluminous A2-subtype granitoids, combined with the newly discovered Na-rich granitoids and calc-alkaline mafic rocks, suggests that the tectonic setting of the JLJB is back-arc basin. |
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