| 内蒙古东部大石寨地区大石寨组火山岩的成因及其大地构造背景 |
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| 引用本文： | 那福超,宋维民,杨雅军,付俊彧,汪岩,刘英才,孙巍,钱程,秦涛,马永非,伍月,钟辉.内蒙古东部大石寨地区大石寨组火山岩的成因及其大地构造背景[J].地球科学,2021,46(7):2403-2422. |
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| 作者姓名： | 那福超 宋维民 杨雅军 付俊彧 汪岩 刘英才 孙巍 钱程 秦涛 马永非 伍月 钟辉 |
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| 作者单位： | 中国地质调查局沈阳地质调查中心, 辽宁沈阳 110034 |
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| 基金项目： | 中国地质调查局项目DD20190360中国地质调查局项目DD20190383 |
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| 摘 要： | 内蒙古东部早二叠世火山岩的成因和动力学背景对于揭示兴安地块和松嫩地块的拼合作用具有重要意义.通过选取大石寨地区大石寨组基-中性火山岩为研究对象，开展LA-ICP-MS锆石U-Pb定年、全岩主微量和锆石原位Lu-Hf同位素分析，旨在讨论其岩石成因和构造背景，为制约兴安地块与松嫩地块的拼合过程和探讨兴蒙造山带东段的构造演化提供更多信息.大石寨组基-中性火山岩包括变细碧岩、变玄武岩、碎屑岩化玄武安山岩、玄武安山质晶屑凝灰岩、绿泥石化安山岩、杏仁状安山岩、安山质晶屑凝灰岩等.锆石LA-ICP-MS U-Pb同位素定年结果显示，变细碧岩和绿泥石化安山岩样品的206Pb/238U年龄加权平均值分别为286.0±4.3 Ma（MSWD=0.14）和286.0±3.3 Ma（MSWD=0.14），说明大石寨组基-中性火山岩喷发于早二叠世，反映了早二叠世的构造岩浆作用事件.岩石地球化学研究表明，大石寨组基-中性火山岩为一套弱过铝质-偏铝质富钠质亚碱性玄武岩-玄武安山岩-安山岩岩石组合，以拉斑系列为主，部分兼具拉斑性和钙碱性特征，相对富集大离子亲石元素（LILE，Ba、U、K等）和轻稀土元素（LREE，La、Ce），亏损高场强元素（HFSE，如Nb、Ta等）.锆石原位Lu-Hf资料显示，变细碧岩和绿泥石化安山岩具有较高的正εHf（t）值（6.68~12.94，8.41~12.31）和相近的单阶段模式年龄（TDM1=438~589 Ma和413~668 Ma）.综合研究表明，大石寨组基-中性火山岩来源于亏损地幔，在岩浆演化过程中经历了单斜辉石、橄榄石和铁镁氧化物的分离结晶作用，并遭受过较强烈的地壳混染作用.结合区域地质资料，大石寨地区大石寨组火山岩形成于陆内伸展的构造背景，而非俯冲背景的产物，这表明兴安地块与松嫩地块的拼合事件发生在早二叠世之前.同时通过对比区域上早中二叠世火山岩的地球化学特征以及其他地质资料，认为内蒙古中东部早中二叠世火山岩是陆内伸展作用的产物，而区域上的伸展作用可能起始于早石炭世.
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| 关 键 词： | LA-ICP-MS U-Pb定年 地球化学 构造背景 大石寨组 内蒙古东部 |
| 收稿时间： | 2020-09-15 |
Petrogenesis and Tectonic Setting of Volcanic Rocks of Dashizhai Formation in Dashizhai Area,Eastern Inner Mongolia |
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| Na Fuchao,Song Weiming,Yang Yajun,Fu Junyu,Wang Yan,Liu Yingcai,Sun Wei,Qian Cheng,Qin Tao,Ma Yongfei,Wu Yue,Zhong Hui.Petrogenesis and Tectonic Setting of Volcanic Rocks of Dashizhai Formation in Dashizhai Area,Eastern Inner Mongolia[J].Earth Science-Journal of China University of Geosciences,2021,46(7):2403-2422. |
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| Authors: | Na Fuchao Song Weiming Yang Yajun Fu Junyu Wang Yan Liu Yingcai Sun Wei Qian Cheng Qin Tao Ma Yongfei Wu Yue Zhong Hui |
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| Abstract: | The petrogenesis and geodynamic setting of Early Permian volcanic rocks in eastern Inner Mongolia, hold a key to understanding the amalgamation of Xing'an block and Songnen block. This study carry out LA-ICP-MS zircon U-Pb dating, whole rock major trace and zircon in situ Lu-Hf isotopic analysis of basic-intermediate volcanic rocks of Dashizhai formation in Dashizhai area with the aim of investigating their petrogenesis and unraveling the geodynamic setting of their emplacement, so as to provide more information for constraining the amalgamation process of Xing'an block and Songnen block, and for exploring the tectonic evolution of the eastern part of the Xing'an-Inner Mongolia Orogenic Belt (XMOB). The basic-intermediate volcanic rocks of Dashizhai Formation include metaspilite, metabasalt, clastic basaltic andesite, basaltic andesite, chloritized andesite, amygdaloid andesite, andesitic crystalline tuff, etc. LA-ICP-MS zircon U-Pb ages of 286.0±4.3 Ma (MSWD=0.14) and 286.0±3.3 Ma (MSWD=0.14) from the metaspilite and chloritized andesite uniformly indicate that these basic-intermediate rocks of Dashizhai Formation erupted in the Early Permian, representing a violent tectono-magmatism event. Geochemically, these volcanic rocks are a set of Na rich subalkaline basalt-basaltic andesite-andesite association, most of them are dominated by tholeiitic series, and some of them have both tholeiitic and calc alkaline characteristics. These rocks are characterized by an enrichment in large ion lithophile elements (LILEs, such as Ba, U, K) and light rare earth elements (LREE, La, Ce), and a depletion in high field strength elements (HFSEs, such as Nb and Ta). Most magmatic zircons of the metaspilite and chloritized andesite show positive εHf(t) values (6.68-12.94 and 8.41-12.31 resectively) and similar single-stage model ages (TDM1=438-589 Ma and 413-668 Ma resectively). In summary, the basic-intermediate volcanic rocks of Dashizhai Formation in Dashizhai area are derived from depleted mantle, and experienced fractional crystallization of clinopyroxene, olivine and iron magnesium oxide in the process of magma evolution, and suffered from strong crustal contamination.Combined with the regional geological data, the volcanic rocks of Dashizhai formation in Dashizhai area were formed in the tectonic setting of intracontinental extension rather than subduction background, which indicates that the amalgamation of Xing'an block and Songnen block occurred before the Early Permian. At the same time, by comparing the geochemical characteristics and other geological data of the Early-Middle Permian volcanic rocks in the region, this paper considers that the Early-Middle Permian volcanic rocks in the mid-eastern Inner Mongolia are the products of intracontinental extension, and the regional extension may have originated from the Early Carboniferous. |
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