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桂西南凭祥火山岩年代学、地球化学及Hf同位素研究——对古特提斯洋最晚北向俯冲事件的启示
(1.桂林理工大学 广西隐伏金属矿产勘查重点实验室, 广西 桂林 541004;2.中国科学院新疆生态与地理研究所新疆矿产资源研究中心, 新疆 乌鲁木齐 830011)
GEOCHRONOLOGY, GEOCHEMISTRY AND HF ISOTOPES OF VOLCANIC ROCKS IN PINGXIANG AREA, SOUTHWEST GUANGXI: IMPLICATIONS FOR THE LATEST STAGE OF PALEO-TETHYAN OCEAN NORTHWARD SUBDUCTION
(1.Guangxi Hidden Mineral Exploration Center, College of Earth Sciences, Guilin University of Technology, Guilin 541004, Guangxi, China;2.Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, Xinjiang, China)
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投稿时间:2019-08-20    修订日期:2019-10-01
中文摘要: 华南西南缘凭祥地区位于特提斯构造域东端,华南与印支陆块碰撞缝合带的北部,该区出露的三叠纪中酸性火山岩是古特提斯洋俯冲过程中在华南陆块边缘形成的大陆弧产物,这些火山岩同时携带的大量来自华南陆块基底的捕获锆石为华南陆块的构造热事件研究将提供重要的信息。对凭祥地区三叠系北泗组英安岩进行了同位素年代学、地球化学及锆石Hf同位素研究,获得了一个英安岩样品的加权平均年龄为(227.8±1)Ma,这些英安岩具有高SiO2、K2O含量,极低的MgO、MnO和CaO含量,富集大离子亲石元素(Rb、Ba、Th和U)和亏损高场强元素(Nb、Ta)的特点,显示了典型的岛弧岩浆作用特征,代表古特提斯洋向北俯冲至华南陆块之下形成的大陆弧产物。其余两个英安岩样品中的70粒锆石主要为来自华南陆块基底的捕获锆石,其年龄数据变化区间较大,为1010~231 Ma,这些捕获锆石U-Pb年龄频谱分布主要集中在四个区间:11010~800 Ma(峰值900 Ma),其锆石的εHft)值为4.5~15.1,响应扬子和华夏陆块之间聚合-裂解-再聚合的构造演化事件,反应了其幔源岩浆的广泛参与;2720~620 Ma(峰值680 Ma)响应南华纪已拼合的扬子-华夏陆块的再次发生裂解;3490~400 Ma(峰值450 Ma),其锆石的εHft)值为2.2~-7.8,响应华南早古生代加里东运动有关的壳-幔相互作用岩浆事件;4280~230 Ma(峰值250 Ma),其锆石εHft)值为-13.6~-16.5,地壳模式年龄为2.3~2.1 Ga,代表了印支与华南陆块之间古特提斯洋俯冲闭合的岩浆事件。文章的研究结果揭示了凭祥北泗组英安岩与华南陆块的亲缘性,其结晶年龄限定了华南与印支陆块之间的古特提斯洋俯冲结束、陆-陆开始碰撞的最晚时限为中-晚三叠纪。
Abstract:Pingxiang area located in the southwest margin of Souch China Block (SCB) and north side of the collision zone between the South China and Indochina plate, tectonically belongs to the eastern part of the Tethyan tectonic domain. The Triassic intermediate-acid volcanics exposed in the Pingxiang area are continental arcs formed during the subduction of the Paleo-Tethysan ocean. They carried a large number of captured zircons sourced from the basement of SCB, which provided important information for the tectono-thermal events in SCB. In this paper, the geochronology, geochemistry and zircon Hf isotope studies were carried out on the dacites from Triassic Beisi Formation in Pingxiang area, and a weighted average age yeild 227.8±1.3 Ma from one dacite sample was obtained, representing its crystallization age. Geochemically, the dacites have high contents of SiO2, K2O, and low MgO, MnO and CaO contents, enriched in LILEs (Rb, Ba, Th and U) and depleted in HFSEs (Nb, Ta), which shows a typical characteristics of island arc magma, representing the continental arc products formed by the northward subduction of the Paleo-Tethysan ocean. The U-Pb age frequency distribution of captured zircons from another two dacite samples is mainly concentrated in (1)1010~800 Ma (peak 900 Ma), and the zircon εHf(t) value is 4.5~15.1, responding to the tectonic evolution events of the convergence-rifting-reconvergence between the Yangtze and Cathaysia blocks and the participation of the mantle-derived magma; (2) 720~620 Ma (peak 680 Ma), responding to the re-rifting of the Yangtze-Cathaysia blocks; (3) 490~400 Ma (peak 450 Ma), the zircon εHf(t) value is 2.2~-7.8, responding to the tectono-magmatic event of crust-mantle interaction related to the Caledonian movement in Early Paleozoic in SCB; (4) 280~230 Ma (peak 250 Ma), the zircon εHf(t) value is -13.6~-16.5, and the crustal model age is 2.3~2.1 Ga, which represents the magmatic event of the Paleo-Tethysan Ocean final subduction to closure between Indochina and South China. The study results reveal the dacites from Beisi formation have an intimate affinity with SCB, and its crystallization age constrains the latest time of the Paleo-Tethysan Ocean subduction ending to closure between SCB and Indochina block at least last to Middle to Late Triassic.
文章编号:     中图分类号:P588.14;P597.3    文献标志码:
基金项目:国家自然科学基金(41888101,41562005,41772059);广西自然科学基金杰出青年科学基金(2018GXNSFFA281009);广西八桂学者项目(2018,有色金属成矿理论与勘查技术);广西中青年教师基础能力提升项目(2019KY0272)
引用文本:
李政林,刘希军,肖文交,鲍厚银,时毓,刘磊,廖帅,覃显著.桂西南凭祥火山岩年代学、地球化学及Hf同位素研究——对古特提斯洋最晚北向俯冲事件的启示[J].地质力学学报,2019,25(5):932-946DOI:10.12090/j.issn.1006-6616.2019.25.05.076
LI Zhenglin,LIU Xijun,XIAO Wenjiao,BAO Houyin,SHI Yu,LIU Lei,LIAO Shuai,QIN Xianzhu.GEOCHRONOLOGY, GEOCHEMISTRY AND HF ISOTOPES OF VOLCANIC ROCKS IN PINGXIANG AREA, SOUTHWEST GUANGXI: IMPLICATIONS FOR THE LATEST STAGE OF PALEO-TETHYAN OCEAN NORTHWARD SUBDUCTION[J].,2019,25(5):932-946DOI:10.12090/j.issn.1006-6616.2019.25.05.076

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