| 东昆仑祁漫塔格寒武纪岛弧:来自拉陵高里河地区玻安岩型高镁安山岩/闪长岩锆石U-Pb年代学、地球化学和Hf同位素证据 |
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| 引用本文： | 王秉璋,潘彤,任海东,王涛,赵志逸,封建平,张金明.东昆仑祁漫塔格寒武纪岛弧:来自拉陵高里河地区玻安岩型高镁安山岩/闪长岩锆石U-Pb年代学、地球化学和Hf同位素证据[J].地学前缘,2021,28(1):318-333. |
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| 作者姓名： | 王秉璋 潘彤 任海东 王涛 赵志逸 封建平 张金明 |
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| 作者单位： | 青海省地质调查院青藏高原北部地质过程与矿产资源重点实验室,青海西宁810012;青海省地质矿产勘查开发局,青海西宁810001;青海大学地质工程系,青海西宁810012 |
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| 基金项目： | 国家自然科学基金项目(41762006);国家自然科学基金项目(41862011);第二次青藏高原综合科学考察研究(STEP)项目(2019QZKK0702) |
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| 摘 要： | 祁漫塔格构造带是东昆仑造山带的重要组成部分,在青藏高原北部早古生代汇聚板块边缘地质研究中具有重要意义。祁漫塔格构造带在早古生代通常被认为是弧或弧后盆地,但其早期形成阶段的地质记录尚未报道,初始俯冲的时代也有待进一步限定。本文选择了祁漫塔格东段拉陵高里河地区祁漫塔格群火山岩和闪长岩进行岩石学、地球化学、锆石U-Pb年龄学和Hf同位素研究,探讨了岩石成因和构造意义。火山岩以安山岩为主,安山岩SiO2含量中等(54.02%~63.99%),具有低TiO2(0.19%~0.24%)、Al2O3(10.67%~12.86%)、P2O5(0.03%~0.05%)和低FeOT/MgO比值(0.80%~1.04)的特征,具有高的MgO(7.86%~11.44%)和Mg#(63~69);闪长岩SiO2含量为53.62%~55.81%,也具有低TiO2(0.19%~0.25%)、Al2O3(10.58%~11.52%)、P2O5(0.02%~0.04%)和低FeOT/MgO比值(0.9~1.0)的特征,同样具有高的MgO(9.86%~11.63%)和Mg#(64~66)的特点。高镁安山岩和闪长岩微量元素组成相近,Th(0.22~1.23 μg/g)、Rb(4.11~16.11 μg/g)和Ba(66.7~166 μg/g)含量低,Cr(286~668 μg/g)和Ni(57~181 μg/g)含量高,δEu=0.91~1.47,Sr/Y比值(19.7~36.1)较低,∑REE含量介于11.8~27.3 μg/g,(La/Yb)N = 1.3~4.3,轻重稀土分馏弱。在微量元素原始地幔标准化图解上大离子亲石元素Sr、Ba和Pb具明显的正异常,高场强元素Ta、Nb和Ti具有明显的负异常。高镁安山岩LA-ICP-MS 锆石U-Pb同位素年龄为519 Ma;闪长岩LA-ICP-MS 锆石U-Pb同位素年龄为520 Ma和516 Ma,两者锆石Hf同位素组成相似,εHf(t)值分布在+10.5~+15.8。上述研究结果表明,祁漫塔格东段拉陵高里河地区高镁安山岩/闪长岩源于亏损的地幔楔的部分熔融,形成于原特提斯洋俯冲早期的岛弧环境。本研究进一步证明祁漫塔格构造带古洋盆俯冲时代早于520 Ma,该认识也为恢复东昆仑造山带原特提斯洋早期俯冲演化历史提供了重要地质资料。
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| 关 键 词： | 高镁安山岩/闪长岩 寒武纪 祁漫塔格 东昆仑 |
| 收稿时间： | 2020-11-13 |
Cambrian Qimantagh island arc in the East Kunlun orogen:Evidences from zircon U-Pb ages,lithogeochemistry and Hf isotopes of high-Mg andesite/diorite from the Lalinggaolihe area |
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| WANG Bingzhang,PAN Tong,REN Haidong,WANG Tao,ZHAO Zhiyi,FENG Jianping,ZHANG Jinming.Cambrian Qimantagh island arc in the East Kunlun orogen:Evidences from zircon U-Pb ages,lithogeochemistry and Hf isotopes of high-Mg andesite/diorite from the Lalinggaolihe area[J].Earth Science Frontiers,2021,28(1):318-333. |
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| Authors: | WANG Bingzhang PAN Tong REN Haidong WANG Tao ZHAO Zhiyi FENG Jianping ZHANG Jinming |
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| Institution: | 1. Key Laboratory of the Northern Qinghai-Tibet Plateau Geological Processes and Mineral Resources,Qinghai Geological Survey Institute, Xining 810012, China2. Bureau of Geological Exploration and Development of Qinghai Province, Xining 810001, China3. Department of Geological Engineering, Qinhai University, Xining 810016, China |
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| Abstract: | The Qimantagh belt is an important component of the East Kunlun orogen and plays a key role in reconstructing the early Paleozoic convergent history of the northern Tibetan Plateau. The Qimantagh belt used to be interpreted as part of early Paleozoci arc or back-arc basin, however, the geological records of the early-stage of subduction have seldom been reported and the age of subduction initiation still remains poorly constrained. In this paper, we studied the petrology, geochemistry, zircon U-Pb ages and Hf isotopes of volcanic rocks and diorite from the Qimantagh Group of the Lalinggaolihe area and discussed their petrogenesis and tectonic significance. Volcanic rocks are dominated by andesites with moderate SiO2 contents (54.02%-63.99%), low TiO2(0.19%-0.24%), Al2O3(10.67%-12.86%) and P2O5(0.03%-0.05%) contents and low FeOT/MgO ratios (0.80-1.04), high MgO contents (7.86%-11.44%) and Mg# (63-69). Diorites have moderate SiO2 contents (53.62%-55.81%), low TiO2(0.19%-0.25%), Al2O3(10.58%-11.52%) and P2O5(0.02%-0.04%) contents and low FeOT/MgO ratios (0.9-1.0) with high MgO contents (9.86%-11.63%) and Mg# (64-66). The high-Mg andesites and diorites share similar trace-elements compositions and have low Th(0.22-1.23 μg/g), Rb(4.11-16.11 μg/g) and Ba(66.7-166 μg/g) contents, high Cr(286-668 μg/g) and Ni(57-181 μg/g) contents, moderate δEu (0.91-1.47) and low Sr/Y ratios (19.7-36.1). They also have low total REE contents (11.8-27.3 μg/g) and (La/Yb)N values (1.3-4.3), indicating weak LREE/HREE fractionation. The primitive mantle-normalized trace-element diagram shows positive Sr, Ba and Pb anomalies and negative Ta, Nb and Ti anomalies. The LA-ICP-MS U-Pb zircon ages of high-Mg andesites and dorites are 519 and 520/516 Ma, respectively. Both zircons share similar Hf isotopic compositions with εHf(t) of +10.5 to +15.8. These results indicate that the andesites and diorites from the Lalinggaolihe area originated from partial melting of depleted mantle wedge in island arc setting during the early stage of subduction of the Proto-Tethyan Ocean. This study further demonstrates that the subduction of paleo-ocean basin in the Qimantagh belt predated 520 Ma, which improves the understanding on the early-stage subduction history of the Proto-Tethys Ocean in the East Kunlun orogen. |
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| Keywords: | high-Mg andesite/diorite Cambrian Qimantagh East Kunlun |
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