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引用本文:刘亮,李江涛,杨鹏涛,何学锋,苏画,梁斌,杨宇东,江辉. 新疆博格达造山带石炭纪的构造属性:来自辉长岩年代学与地球化学的证据[J]. 中国地质, 2020, 47(3): 725-741.
LIU Liang,LI Jiangtao,YANG Pengtao,HE Xuefeng,SU Hua,LIANG Bin,YANG Yudong,JIANG Hui. The Carboniferous tectonic attributes of the Bogda orogenic belt in Xinjiang: Evidence from gabbro chronology and geochemistry[J]. Geology in China, 2020, 47(3): 725-741(in Chinese with English abstract).
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新疆博格达造山带石炭纪的构造属性:来自辉长岩年代学与地球化学的证据
刘亮1,2, 李江涛2,3, 杨鹏涛1,2, 何学锋1, 苏画1, 梁斌1,2, 杨宇东1, 江辉1
1.四川省地质矿产勘查开发局川西北地质队, 四川 绵阳 621010;2.西南科技大学环境与资源学院, 四川 绵阳 621010;3.乐山市自然资源局, 四川 乐山 614000
摘要:
博格达造山带广泛分布着基性侵入岩体,其成因对正确认识该区地球动力学背景具有重要意义。鉴于此,本文对位于博格达造山带西段的辉长岩进行了岩石学、地球化学及锆石U-Pb年代学研究,探讨其岩石成因及构造属性,以期为解决博格达造山带的地质构造演化提供依据。岩石地球化学分析结果显示,辉长岩SiO2含量介于48.08%~51.03%,全碱(ALK)含量为3.09%~4.39%(小于5%),富CaO(6.87%~11.41%)、贫Al2O3(12.59%~18.49%),MgO含量介于3.78%~7.66%,Mg#值为31.75~65.73(均值为47.03),铝饱和指数值(A/CNK=0.60~0.80),属准铝质中钾钙碱性岩石系列。岩石稀土元素含量较低(36.30×10-6~147.72×10-6),轻重稀土之间以及轻重稀土内部不存在明显的分馏过程;微量元素中Th、Ta、Nb元素明显亏损,Ti元素亏损不明显以及U元素的轻微富集,具大陆裂谷岩浆活动特点。根据有关微量元素、稀土元素的相关图解比值,指示该区辉长岩岩浆源于亏损的岩石圈地幔,侵位过程中受到了地壳物质的混染,分异演化程度较低,为原始尖晶石相橄榄岩较高程度的部分熔融,形成于板内裂谷环境。此外,辉长岩LA-ICP-MS锆石U-Pb定年结果表明,其形成时代为(305.0±1.6)Ma(晚石炭世末期),处于博格达裂谷火山活动期晚期,为博格达西段裂谷作用由全面伸展向局限伸展转换的标志。综合区域地质资料分析,认为晚古生代期间(早石炭世—早二叠世),博格达造山带存在大面积的与裂谷演化有关的岩浆活动,造山带是在裂谷基础上发展起来,其形成与康古尔塔格洋推动着准噶尔—吐哈地块向北俯冲作用有关。
关键词:  辉长岩  地球化学  锆石U-Pb定年  大陆裂谷  地质调查工程  博格达造山带
DOI:10.12029/gc20200312
分类号:P588.12+4;P541
基金项目:新疆维吾尔自治区地质勘查基金项目“新疆东天山甘河子一带1∶5万区域地质矿产调查”项目(A14-1-LQ03)及国家自然科学基金项目(41472310)联合资助。
The Carboniferous tectonic attributes of the Bogda orogenic belt in Xinjiang: Evidence from gabbro chronology and geochemistry
LIU Liang1,2, LI Jiangtao2,3, YANG Pengtao1,2, HE Xuefeng1, SU Hua1, LIANG Bin1,2, YANG Yudong1, JIANG Hui1
1.Northwest Sichuan Geological and Mineral Exploration Party, Mianyang 621010, Sichuan, China;2.School of Environment and Resource, Southwest University of Science and Technology, Mianyang 621010, Sichuan, China;3.Leshan Natural Resources Bureau, Leshan 614000, Sichuan, China
Abstract:
Basic intrusive rock masses are extensively developed in Bogda orogenic belt, and their origin is of great significance to the correct understanding of the geodynamic background of this area. In this paper, the authors studied systematically petrology, geochemistry and zircon U-Pb geochronology of gabbro in the west of Bogda orogenic belt, in order to discuss their petrogenesis and tectonic significance and then to provide a basis for solving geological tectonic evolution of Bogda orogenic belt. Petrogeochemical analysis shows that their SiO2 values range from 48.08% to 51.03%, and ALK values range from 3.09% to 4.39% (less than 5%), and that they are rich in CaO (6.87%-11.41%), and depleted in Al2O3 (12.59%-18.49%). The MgO values range from 3.78% to 7.66%, Mg#=31.75-65.73 (47.03 on average), and A/CNK=0.60-0.80, indicating that the rocks belong to metaluminous intermediate K calc-alkaline rock series. The analysis also shows that they have low REE (36.30×10-6-147.72×10-6), with no obvious fractionation between light and heavy rare earth elements and between heavy rare earth elements. They are obviously depleted in Th, Ta, Nb elements, with no obvious loss of Ti and slight enrichment of U element, showing the characteristics of continental rift magmatism. According to the relevant diagram and the ratio of trace elements and rare earth elements, the gabbro magma probably originated from depleted lithospheric mantle, with the contamination of the crust; their differentiation evolution degree was low; they experienced higher degree of partial melting of the original phase spinel peridotite, and were formed in the intraplate rift environment. Moreover, gabbro LA-ICP-MS zircon U-Pb dating results show that the formation age is (305.0±1.6) Ma, suggesting the late period of the Bogda rift volcanic activity in late Carboniferous. All these data indicate that the west of Bogda rift underwent a conversion from the overall extension stage to the confined extension stage. The analysis of regional geological data shows that there existed a large rift evolution related to magmatism during Late Paleozoic (Early Carboniferous-Early Permian), and the orogenic belt was developed on the basis of rifting, with its formation related to the northward subduction of the Junggar-Turpan-Hami block driven by the Kangurtag Ocean.
Key words:  gabbro  geochemistry  zircon U-Pb dating  continental rift  geological survey engineering  Bogda orogenic belt