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

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±2.4 Ma(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(K₂O/Na₂O＞1)、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ε_Nd(t)(-2.0~+0.5) 和较老的两阶段模式(T_DM2)年龄(1.15~1.35 Ga)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. 

Ages,Origin and Tectonic Significance of Halaerci Granites from Northeastern Part of Chinese Altay Mountains

In order to study the chronological, geochemical characteristics and tectonic setting of the Halaerci granite from Altay area, the LA-MC-ICPMS zircons U-Pb dating method was employed to assess the ages and Nd isotope composition, preceded by their petrologcial and geochemical studies. In addition, the authors aim to provide more evidences for the structural evolution of Altay tectonic belt by making a comparison with other granites from central Altay orogenic belt. The exposed Halaerci granites of central Altay tectonic belt are dominated by granodiorite, monzonite and syenogranite. LA-ICP-MS zircon U-Pb chronology study suggests that formation age is from 454.8±2.4 Ma (MSWD=0.32), which belongs to the Late Ordovician magma activity. The study of geochemistry indicates that rock is characterized by high silicon, enriched alkali and high potassium (K₂O/Na₂O > 1) and low titanium, low magnesium and low phosphorus. Average (A/CNK) is 1.5 and corundum molecular content of CIPW calculation is greater than 1, which shows a high potassium calc-alkaline peraluminous granite characteristics. The granites are relatively enriched in light rare earth elements, while flat in heavy rare earth elements, with significant Eu negative anomaly, enrichment of Th and Rb, depletion of Sr, Ti and P elements, pronounced Nb, Ta and Ti negative anomalies, which shows the initial arc characteristic of magmatic rocks. Its ε_Nd(t) is close to 0 (-2.0 to 0.5) and old two-phase model (T_DM2) age (1.15 to 1.35) Ga indicate its source area contains more crust-derived source components with a certain amount mantle source materials. Comprehensive analysis and study suggest that Halaerci granites may be composed of partial melting of argillaceous sandstone enriched with muscovite and biotite under low pressure and high temperature. Its source area has residual plagioclase, ilmenite and apatite and mixed with mantle source materials at the same time. It is concluded that Halaerci granites formed in the active continental margin squeezing environment when the heat by local extentional stress reduction and abnormal uneven mantle materials rise led to partial melting of upper crust to mix with mantle source materials.