| 北山造山带早泥盆世埃达克岩的发现及地质意义 |
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| 引用本文： | 杨镇熙,丁书宏,张晶,樊新祥,孔维琼,赵吉昌,荆德龙.北山造山带早泥盆世埃达克岩的发现及地质意义[J].岩石矿物学杂志,2021,40(2):185-201. |
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| 作者姓名： | 杨镇熙 丁书宏 张晶 樊新祥 孔维琼 赵吉昌 荆德龙 |
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| 作者单位： | 甘肃省地质矿产勘查开发局 第四地质矿产勘查院, 甘肃 酒泉 735000;兰州新区自然资源局, 甘肃 兰州 730000;中国地质调查局 西安地质调查中心, 陕西 西安 710054 |
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| 基金项目： | 甘肃省基础地质调查项目（甘财经二[2017]105号,甘财经二[2018]59号,甘财经二[2019]39号,甘资财环[2020]28号）;陕西省自然科学基础研究计划（2019JQ-934） |
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| 摘 要： | 北山造山带位于中亚巨型造山带南缘,是剖析中亚造山带南缘增生构造过程的关键地区之一,古亚洲洋闭合时间存在较大争议,聚焦于泥盆纪古亚洲洋仍在俯冲还是已经闭合。作者在北山造山带南缘黑山头一带首次识别出具典型埃达克岩特征的中酸性侵入体,对其进行了岩石地球化学和锆石U-Pb年代学研究。黑山头岩体中花岗闪长岩LA-ICP-MS锆石U-Pb加权平均年龄为407.7±1.6 Ma,形成于早泥盆世。地球化学数据表明,黑山头岩体为过铝质,属钙碱性系列,具典型埃达克岩特征:高硅(SiO_2=60.85%～67.81%)、高铝(Al_2O_3=15.59%～16.98%)、低镁(MgO=0.55%～1.53%,Mg~#=0.36～0.46)、富钠贫钾(Na_2O=2.65%～3.54%,K_2O=1.09%～3.16%,Na_2O/K_2O=0.96～2.44)、高Sr(Sr=253×10~(-6)～487×10~(-6))、低Y和Yb(Y=5.65×10~(-6)～16.70×10~(-6),Yb=0.37×10~(-6)～0.96×10~(-6))、高Sr/Y值(25.75～73.58);轻稀土元素富集,轻重稀土元素分馏明显,样品不具明显的Eu异常(0.66～1.31,平均0.92);微量元素富集大离子亲石元素Rb、K、Th、U,亏损高场强元素Nb、Ta、Ti、P。地球化学特征显示其为俯冲洋壳部分熔融形成的埃达克岩,残留相为石榴子石+金红石。结合前人研究认识,认为柳园洋(古亚洲洋)具有自西向东呈"剪刀式"闭合的特征,柳园洋(古亚洲洋)在早泥盆世仍处于俯冲碰撞阶段,早石炭世是北山地区古生代洋盆闭合时限上限。
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| 关 键 词： | 埃达克岩 锆石U-Pb年龄 岩石地球化学 岩石成因 北山造山带 |
| 收稿时间： | 2020/8/19 0:00:00 |
The discovery of Early Devonian adakites in Beishan orogenic belt and its geological significance |
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| YANG Zhen-xi,DING Shu-hong,ZHANG Jing,FAN Xin-xiang,KONG Wei-qiong,ZHAO Ji-chang,JING De-long.The discovery of Early Devonian adakites in Beishan orogenic belt and its geological significance[J].Acta Petrologica Et Mineralogica,2021,40(2):185-201. |
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| Authors: | YANG Zhen-xi DING Shu-hong ZHANG Jing FAN Xin-xiang KONG Wei-qiong ZHAO Ji-chang JING De-long |
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| Institution: | Fourth Institute of Geological and Mineral Exploration, Gansu Bureau of Geology and Mineral Resources, Jiuquan 735000, China;Lanzhou New Area County Natural Resource Bureau, Lanzhou 730000, China; Xi''an Center of Geological Survey, China Geological Survey, Xi''an 710054, China |
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| Abstract: | Located on the southern margin of the Central Asian giant orogenic belt, the Beishan orogenic belt is one of the key areas for dissecting the accretionary tectonic process of the southern margin of the Central Asian orogenic belt. Researchers have a great controversy about the closing time of the Paleo-Asian Ocean and focus on whether the Devonian ancient Asian Ocean was still subducting or closed. In this study, the authors firstly identified a pluton with typical adakite characteristics in Heishantou area on the southern margin of the Beishan orogenic belt. The geochemical characteristics and zircon U-Pb chronology of the pluton were studied to discuss its genesis and geodynamic significance. The Heishantou pluton is dominated by granodiorite and partially consist of tonalite. The weighted average age of granodiorite LA-ICP-MS zircon U-Pb is 407.7±1.6 Ma. Geochemical data show that the Heishantou pluton belong to peraluminous, calc-alkaline series, with typical adakite characteristics:high silicon (SiO2=60.85%~67.81%), high alumina (Al2O3=15.59%~16.98%), low magnesium (MgO=0.55%~1.53%,Mg#=0.36~0.46), rich sodium and poor potassium (Na2O=2.65%~3.54%,K2O=1.09%~3.16%,Na2O/K2O=0.96~2.44), high Sr (Sr=253×10-6~487×10-6) low Y and Yb (Y=5.65×10-6~16.70×10-6,Yb=0.37×10-6~0.96×10-6) compositions, with high Sr/Y ratio (25.75~73.58). Their light rare earth elements (LREE) are enriched, with obvious light and heavy rare earth fractionation. The samples do not have obvious Eu anomaly (0.66~1.31, averaging 0.92). Moreover, trace element composition is characterized by enrichment of LILEs such as Rb, K, Th and U, and depletion of high field strength elements HSFEs such as Nb, Ta, Ti and P. Geochemical characteristics show that these adakites were formed by partial melting of the subducting oceanic crust, and the residual minerals of the crust sources might have been garnet and rutile. Based on this study and regional geological data, the authors hold that the Liuyuan Ocean (Paleo-Asian Ocean) was still in the subduction and collision stage during the Early Devonian and had the characteristics of "scissoring" closure from west to east. The upper limit of the closing time of the Paleozoic ocean basin is Early Carboniferous in the Beishan area. |
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| Keywords: | adakite zircon U-Pb age petrology and chemistry petrogenesis Beishan orogenic belt |
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