中国阿尔泰东北部哈拉尔次花岗岩的年龄、成因及构造意义

发布时间：2018-08-26 21:36

【摘要】：在岩石地球化学研究基础上,揭示哈拉尔次花岗岩的成因、侵位时代及构造背景,进行锆石U-Pb及Nd同位素测试,并与阿尔泰造山带内其他花岗岩进行对比,有助于为阿尔泰造山带构造演化提供依据.出露于中阿尔泰构造带的哈拉尔次花岗岩主要岩石类型有花岗闪长岩、二长花岗岩、正长花岗岩,LA-ICP-MS锆石U-Pb年代学研究结果表明,其形成时代为454.8±2.4Ma(MSWD=0.32),为晚奥陶世岩浆活动产物.地球化学研究表明,岩石具有高硅、富碱、高钾(K_2O/Na_2O1)、低钛、低镁及低磷等地球化学特征,铝饱和指数(A/CNK)平均为1.05,CIPW计算中刚玉分子含量大于1,显示出高钾钙碱性过铝质花岗岩的特征;岩石轻稀土相对富集、重稀土平坦,有显著的Eu负异常,富集Th、Rb,亏损Sr、Ti、P等元素,有明显的Nb、Ta、Ti负异常,显示出火山弧花岗岩的特征;其接近于0的εNd(t)(-2.0~+0.5)和较老的两阶段模式(TDM2)年龄(1.15~1.35Ga)暗示其源区含有较多的壳源组分并有一定量幔源物质加入.综合分析研究表明,哈拉尔次花岗岩可能由富含白云母和黑云母的含泥质杂砂岩在较低压力和较高温度下经历部分熔融形成,其源区有斜长石、钛铁矿和磷灰石的残留,同时幔源物质有一定的混入,形成于活动大陆边缘挤压背景下,局部伸展减压以及异常地幔不均匀上升提供热量,导致中上地壳沉积物发生部分熔融并有少量的幔源物质混入,形成哈拉尔次花岗岩.
[Abstract]:On the basis of petrogeochemical study, the origin, emplacement age and tectonic setting of Harald sub-granites are revealed. Zircon U-Pb and Nd isotopes are measured and compared with other granites in the Altai orogenic belt. It is helpful to provide basis for tectonic evolution of Altai orogenic belt. The main rock types of the Harald sub-granites exposed in the Middle Altay tectonic belt are granodiorite, monzogranite, syenite and LA-ICP-MS zircon U-Pb chronology. The results show that the age of formation is 454.8 卤2.4Ma (MSWD=0.32), which is the product of late Ordovician magmatism. Geochemical studies show that the rocks are characterized by high silicon, alkali rich, high potassium (K_2O/Na_2O1), low titanium, low magnesium and low phosphorus. The average aluminum saturation index (A/CNK) of corundum is more than 1, which shows the characteristics of high potassium calc-alkaline peraluminous granites, the rock is relatively rich in light rare earth, heavy rare earth is flat, there are significant negative Eu anomalies, and Th,Rb, is rich in elements such as Sr,Ti,P, etc. There are obvious Nb,Ta,Ti negative anomalies, showing the characteristics of volcanic arc granites, which are close to 0 蔚 Nd (t) (-2.0 ~ 0.5) and older two-stage model (1.15~1.35Ga) age (1.15~1.35Ga) suggesting that the source region contains more crust-source components and a certain amount of mantle-derived materials. The comprehensive analysis shows that the Harald sub-granite may be formed by partial melting of muddy complex sandstone rich in Muscovite and biotite at lower pressure and higher temperature, and the source areas are plagioclase, ilmenite and apatite residues. At the same time, mantle-derived materials were mixed in to a certain extent, and formed in the background of active continental margin compression. Local stretching and decompression and abnormal mantle inhomogeneous rise provided heat, which led to partial melting of sediments in the upper and middle crust and a small amount of mantle-derived materials mixed in. The Harald sub-granite was formed.
【作者单位】：中国地质大学地球科学与资源学院;中国人民武装警察部队黄金第八支队;长安大学地球科学与资源学院;
【基金】：中国地质调查局地质调查项目(No.12120113071900)
【分类号】：P588.121

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