| 内蒙古东乌旗狠麦温都尔花岗岩SHRIMP锆石U-Pb年龄及其地质意义 |
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| 引用本文： | 程银行,滕学建,辛后田,杨俊泉,冀世平,张永,李艳锋.内蒙古东乌旗狠麦温都尔花岗岩SHRIMP锆石U-Pb年龄及其地质意义[J].岩石矿物学杂志,2012,31(3):323-334. |
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| 作者姓名： | 程银行 滕学建 辛后田 杨俊泉 冀世平 张永 李艳锋 |
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| 作者单位： | 天津地质矿产研究所,天津,300170 |
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| 基金项目： | 国家地质大调查项目(矿调[2005]11-5,1212011121079) |
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| 摘 要： | 内蒙古东乌旗狠麦温都尔地区发育了大量的晚古生代花岗岩,主要岩石类型为二长花岗岩、正长花岗岩。SHRIMP锆石U-Pb同位素定年结果表明,二长花岗岩和正长花岗岩的成岩年龄分别为307.0±1.9 Ma和299.7±5.3 Ma,时代为晚石炭世—早二叠世。岩石地球化学特征显示,主要岩石的SiO2含量为65.65%~71.86%,具富碱(K2O+Na2O为9.59%~9.90%)、富钾(K2O/Na2O为1.00~1.73)的特点,准铝质(A/CNK为0.96~1.00),属高钾钙碱性-钾玄岩系列;岩石富集Rb、Th、K等大离子亲石元素,而亏损Nb、Ta、Sr、P、Ti等元素;稀土元素总量为82.60×10-6~177.58×10-6,(La/Yb)N为4.13~15.37,配分曲线模式略微右倾,δEu为0.44~0.87,中等-弱负铕异常,具岛弧或后碰撞高钾钙碱性花岗岩的特征,结合岩石具块状构造、晶洞构造特征显示为后碰撞花岗岩。综上所述,认为狠麦温都尔高钾钙碱性花岗岩可能为后碰撞早期伸展阶段的产物,与华北板块和西伯利亚板块碰撞作用有关,这一认识为兴蒙造山带晚古生代构造岩浆演化及古亚洲洋闭合的时限提供了新的约束。
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| 关 键 词： | 东乌旗 高钾钙碱性花岗岩 后碰撞 SHRIMP锆石U-Pb年龄 |
| 收稿时间： | 2011/12/22 0:00:00 |
| 修稿时间： | 2012/3/6 0:00:00 |
SHRIMP zircon U-Pb dating of granites in Mahonondor area, East Ujimqin Banner, Inner Mongolia |
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| CHENG Yin-hang,TENG Xue-jian,XIN Hou-tian,YANG Jun-quan,JI Shi-ping,ZHANG Yong and LI Yan-feng.SHRIMP zircon U-Pb dating of granites in Mahonondor area, East Ujimqin Banner, Inner Mongolia[J].Acta Petrologica Et Mineralogica,2012,31(3):323-334. |
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| Authors: | CHENG Yin-hang TENG Xue-jian XIN Hou-tian YANG Jun-quan JI Shi-ping ZHANG Yong and LI Yan-feng |
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| Institution: | (Tianjin Institute of Geology and Mineral Resources,Tianjin 300170,China) |
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| Abstract: | The Mahonondor granites,located in East Ujimqin Banner of Inner Mongolia,are predominated by monzogranite and syenogranite.SHRIMP zircon U-Pb dating shows that the crystallization age of the monzogranite is 307.0±1.9 Ma and that of the syenogranite is 299.7±5.3 Ma.The ages which are between the late Carboniferous and early Permian are consistent with the late Paleozoic magmatic activity age.Geochemical researches indicate that the granite from Mahonondor area in the East Ujimqin Banner of Inner Mongolia is rich in silica(SiO2=65.65%～71.86%),alkali(K2O+Na2O=9.59%～9.90%) and K(K2O/Na2O=1.00%～1.73%),suggesting a typical high-K calc-alkaline to shoshonitic series with the metaluminous feature(A/CNK=0.96～1.04).The rocks are poor in rare earth elements(∑REE=82.60×10-6～157.70×10-6),enriched in LREE (La/Yb)N=4.13～15.37] and LILEs(Rb,Th,K),and depleted in HFSE,especially Nb,Ta,Sr,P and Ti.Similar REE distribution patterns indicate that the Mahonondor granites have the same magma source.The δEu values vary from 0.44 to 0.87,with most rocks having moderate negative Eu anomalies.In addition,massive structure and miarolitic structure point to post-collisional granites.In a word,these characteristics suggest that these high-K calc-alkaline granites in the Mahonondor area were emplaced during post-collisional conversion from compression to extension,and were derived from fractional crystallization of medium-K calc-alkaline diorite-porphyrite,causing collision between the Sino-Korean and Siberian plates during late Devonian to early Carboniferous period.It is shown that the conversion time of the late Paleozoic orogenic process in East Ujimqin area was from 320.1±7.2 Ma to 307±1.9 Ma,the period 286～276 Ma was the developmental stage of post-collisional alkali granites,and Hegenshan oceanic basin had disappeared before 320.1±7.2 Ma.The above results provide new constraints on Mongolia Orogenic Belt tectonic-magmatic evolution in Late Paleozoic and closure of the Paleo-Asian Ocean. |
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| Keywords: | East Ujimqin Banner high-K calc-alkaline granites post collision SHRIMP U-Pb dating |
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