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引用本文:田健,滕学建,刘洋,滕飞,郭硕,何鹏,王文龙. 内蒙古狼山地区早二叠世花岗闪长岩的年代学、地球化学特征及其构造背景[J]. 中国地质, 2020, 47(3): 767-781.
TIAN Jian,TENG Xuejian,LIU Yang,TENG Fei,GUO Shuo,HE Peng,WANG Wenglong. The chronology, geochemistry of the Early Permian granodiorite in Langshan area, Inner Mongolia and its tectonic setting[J]. Geology in China, 2020, 47(3): 767-781(in Chinese with English abstract).
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内蒙古狼山地区早二叠世花岗闪长岩的年代学、地球化学特征及其构造背景
田健, 滕学建, 刘洋, 滕飞, 郭硕, 何鹏, 王文龙
中国地质调查局天津地质调查中心, 天津 300170
摘要:
内蒙古狼山山脉西侧分布有大面积的晚古生代岩浆岩,其时代集中在早石炭世—晚二叠世,不同时代岩浆岩岩石组合对于认识狼山地区晚古生代构造背景具有重要的意义。文章通过岩石学、岩相学、地球化学及Hf同位素等方法,对狼山地区查干乃呼都格一带花岗闪长岩体进行了研究。该岩体岩性为花岗闪长岩,LA-ICP-MS锆石U-Pb年龄显示,其206Pb/238U加权平均年龄为(299±1)~(293±2)Ma。岩石暗色矿物为角闪石及黑云母,富含闪长质包体,P2O5含量与SiO2含量之间显示良好的负相关性,富钠(Na2O含量为3.45%~4.96%),高钠钾比值(Na2O/K2O比值为1.33~2.52),岩石地球化学特征显示花岗岩成因类型为I型花岗岩。岩石具有负的εHft)值(-6.3~-2.0)及TDM2为1437~1704 Ma(平均值为1606 Ma),显示了古—中元古代古老地壳熔融的特点,εHft)-t及角闪石成因图解显示源区有幔源岩浆参与。花岗岩富集大离子亲石元素Rb、K、Pb,不同程度的亏损高场强元素Nb、Ta、P、Ti,轻稀土富集,重稀土亏损,弱的负Eu异常,显示了岩浆弧的地球化学特征。结合晚石炭世—早二叠世狼山地区侵入岩岩石组合为闪长岩+石英闪长岩+花岗闪长岩(英云闪长岩),早—中二叠世大石寨组火山岩岩石组合为玄武岩+玄武安山岩+安山岩+英安岩,总体反映了陆缘弧的岩石组合;狼山地区早二叠世处于大陆边缘弧的构造背景,与华北地块北缘中东部可以对比。
关键词:  内蒙古  狼山地区  早二叠世  花岗闪长岩  大陆边缘弧  地质调查工程
DOI:10.12029/gc20200315
分类号:P588.12+1
基金项目:中国地质调查局项目(DD20160039)资助。
The chronology, geochemistry of the Early Permian granodiorite in Langshan area, Inner Mongolia and its tectonic setting
TIAN Jian, TENG Xuejian, LIU Yang, TENG Fei, GUO Shuo, HE Peng, WANG Wenglong
Tianjin Center of China Geological Survey, Tianjin, 300170, China
Abstract:
There exists a large area of Late Paleozoic magmatic rocks on the western side of Langshan Mountain in Inner Mongolia, whose ages are concentrated on Early Carboniferous to Late Permian. The magmatic rock assemblages of different ages are of great significance for understanding the Late Paleozoic tectonic background of Langshan area. Based on petrology, petrography, geochemistry and Hf isotopes, this study mainly focused on the granodiorites in Chagannaihuduge zone of Langshan area. LA-ICPMS U-Pb dating on two granodiorite samples yielded ages of(299±1)Ma and(293±2)Ma respectively. The mafic minerals in granodiorties are dominated by hornblende and biotite. The geochemical data reveal that the granodiorites are of calc-alkaline nature characterized by enrichment of Na2O (3.45%-4.96%), high Na2O/K2O value (1.33-2.52) and show good negative correlation between P2O5 and SiO2, which is similar to the characteristics of I-type granites. The Hf isotopic signature for granodiorites and their behavior of elemental geochemical characteristics together indicate that their co-magmatic origin mainly derived from Palaeoproterozoic-Mesoproterozoic continental crust and subordinately from mantle-derived magma. The granodiorites show similar patterns on the chondrite-normalized REE patterns, and display relatively high concentration of light rare earth elements (LREEs) but low content of heavy rare earth elements (HREEs) with minor negative Eu anomalies. The overall chemical similarities of these granodiorites on the primitive mantle-normalized variation diagrams display affinity to arc signature. By combining the large scale regional exposures of diorite+quartz diorite+granodiorite rock assemblage and basalt+basaltic andesite+andesite+anganite in Dashizhai Formation, the authors hold that Langshan area was under the tectonic setting of continental margin arc during Early Permian, similar to that of central-eastern part of NNC.
Key words:  Inner Mongolia  Langshan area  Early Permian  granodiorite  continental margin arc  geological survey engineering