| 东昆仑祁漫塔格阿确墩地区侵入岩U-Pb年代学、地球化学及其地质意义 |
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| 引用本文： | 李婷,李猛,胡朝斌,李瑶,孟杰,高晓峰,查显锋.东昆仑祁漫塔格阿确墩地区侵入岩U-Pb年代学、地球化学及其地质意义[J].地球科学,2018,43(12):4350-4363. |
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| 作者姓名： | 李婷 李猛 胡朝斌 李瑶 孟杰 高晓峰 查显锋 |
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| 作者单位： | 1.中国地质调查局西安地质调查中心, 造山带地质研究中心, 陕西西安 710054 |
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| 基金项目： | 中国地质调查局项目DD20160002 |
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| 摘 要： | 祁漫塔格地区岩浆岩的成岩时代和形成环境的确定能对东昆仑造山带加里东期构造演化时限加以约束.对祁漫塔格西北部阿确墩地区石英闪长岩和二长花岗岩进行了年代学和岩石地球化学研究，结果显示，石英闪长岩属准铝质-弱过铝质钙碱性系列岩石；轻重稀土分馏明显，具中等-轻微铕负异常（δEu=0.79~0.90）；相对富集Rb、K、Hf、Zr、Tb、Nd等元素，不同程度地亏损Ba、P、Ti、Nd、Ta、Y；具有I型花岗岩类特征.二长花岗岩属弱过铝质钙碱性系列岩石；轻重稀土分异程度极大，具明显铕负异常（δEu=0.42~0.45）；富集大离子亲石元素（如Rb、K、La、Ce、Nd、Tb等），亏损高场强元素（P、Ti、Nd、Ta）和Ba、Sr、U等元素；为高分异I型花岗岩.Nd/Th、Nb/Ta、Mg#值等指标显示石英闪长岩为壳源特征且受到幔源岩浆的影响，推测是幔源岩浆底侵地壳物质发生部分熔融形成的；二长花岗岩则是壳源的，可能与幔源岩浆底侵诱发的上地壳物质部分熔融有关，且经历了强烈的结晶分离作用.石英闪长岩和二长花岗岩的LA-ICP-MS锆石U-Pb年龄分别为448.8±3.9 Ma和405.2±3.6 Ma，代表其形成时代.石英闪长岩总体显示出与俯冲消减作用有关的岛弧岩浆岩地球化学特征；二长花岗岩在构造环境图解中显示为碰撞背景，但微量元素与同碰撞花岗岩典型特征不符，综合分析认为形成于后碰撞构造背景下.结合区域构造演化，推测东昆仑祁漫塔格地区在晚奥陶世持续处于俯冲消减环境中，早泥盆世之前进入后碰撞造山阶段.
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| 关 键 词： | 东昆仑造山带 祁漫塔格 阿确墩地区 侵入岩 锆石U-Pb定年 地球化学 |
| 收稿时间： | 2018-06-29 |
Zircon U-Pb Geochronology,Geochemistry and Its Geological Implications of Intrusions in Aquedun Area from Qimantag,East Kunlun,China |
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| Abstract: | The determination of formation time and tectonic setting of intrusions in Qimantag area can limit the time of Caledonian tectonic evolution in East Kunlun orogen. Zircon U-Pb geochronology, geochemistry of quartz diorite and monzonite adamellite in Aquedun of northwestern Qimantag area are studied in this paper. Results show that quartz diorite belongs to metaluminous-weakly peraluminous and calc-alkaline series of I-type granite, with moderate Eu negative abnormality (δEu=0.79-0.90) and significant fractionation between light REE and heavy REE, enriched in Rb, K, Hf, Zr, Tb, Nd and depleted of Ba, P, Ti, Nd, Ta, Y.Monzonite adamellite belongs to weakly peraluminous and calc-alkaline series of high-fractionated I-type granite, with significant negative Eu abnormality (δEu=0.42-0.45) and significant fractionation between light REE and heavy REE, enriched in LILE(Rb, K, La, Ce, Nd, Tb) and depleted in HFSE(P, Ti, Nd, Ta) and Ba, Sr, U.The ratios of Nd/Th, Nb/Ta and Mg# of quartz diorite show crustal characteristics with the addition of small amount of mantle-derived materials, produced by partial melting of the continental crust induced by mantle derived magmas underplating. The ratios of Nd/Th, Nb/Ta and Mg# of monzonite adamellite show crustal characteristics, produced by partial melting of the upper continental crust induced by mantle derived magmas underplating and may have experienced the fractional crystallization at the same time. Zircon LA-ICP-MS U-Pb age of the quartz diorite and monzonite adamellite are 448.8±3.9 Ma and 405.2±3.6 Ma, respectively, which represents their formation time. The chemical characteristics of quartz diorite are closely related to the island-arc environments in subduction belt.Monzonite adamellite falls into the zone of collision setting with tectonic setting discrimination diagrams, but the trace elements do not match with typical collision-orogenic granite, so we think monzonite adamellite is post-collision-orogenic granite.Combined with the regional tectonic evolution, it is concluded that Qimantag block of East Kunlun orogen maybe is in the subduction stage in Late Ordovician, and in the post-collision stage before Early Devonian. |
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