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    南天山地块塔格拉克地区二长花岗岩锆石U-Pb年代学、地球化学特征：对壳源岩浆成因和构造背景的限定

    Zircon U-Pb geochronology and geochemistry of the Tagelake monzogranites in South Tianshan block: Constraints on crustal magmatic origin and tectonic setting

      摘要
    • 摘要:
      研究目的 西南天山造山带内塔格拉克地区的长条状岩体位于南天山地块，由二长花岗岩组成。厘定该二长花岗岩的形成机制，对南天山壳源岩浆成因的限定、洋盆俯冲消减及碰撞闭合时限等问题的研究具有重要意义。
      研究方法 本文首次报道了塔格拉克地区二长花岗岩的全岩主量元素、微量元素、锆石U-Pb年代学结果。
      研究结果 LA-ICP-MS锆石年代学研究揭示出塔格拉克地区二长花岗岩成岩年龄为（284.0±1.9）~（284.3±3.2）Ma，为早二叠世花岗岩。岩石主量元素和微量元素分析结果揭示该二长花岗岩具有A型花岗岩特征：（1）SiO2（70.92%~72.78%）含量高，碱质（K2O+Na2O=7.91%~8.44%）含量较高，A/CNK（0.89~0.99）较高，表明二长花岗岩为准铝质岩石，属于高钾钙碱性系列；（2）LREE（196×10-6~280×10-6）相对富集，HREE（22.8×10-6~28.2×10-6）相对亏损，负Eu异常（δEu为0.51~0.64）明显，球粒陨石标准化配分模式呈右倾V型特征；（3）富集Rb、Th和K等大离子亲石元素，相对亏损Nb、Ta、Zr、P和Ti等高场强元素。
      结论 结合区域构造演化，认为塔格拉克地区二长花岗岩形成于后碰撞构造背景。

       

      Abstract:
      This paper is the result of geological survey engineering.
      Objective The Tagelake strip pluton, outcropped at the south Tianshan terrane in Southwestern Tianshan orogenic belt, is composed of monzogranites. Determining the formation mechanism of the monzogranites has important implications for the crust-derived magma origin and the time limit of subduction and ocean basin closure in South Tianshan Mountains.
      Methods In order to determine the formation mechanism of the monzogranites, detailed zircon U-Pb geochronology, major elements and trace elements were firstly conducted.
      Results LA-ICP-MS zircon geochronology study reveals that the monzogranites in the Tagelake area crystallized at (284.0±1.9)-(284.3±3.2) Ma, indicative of an Early Permian pluton. The results of major elements and trace elements reveal that the monzogranites display the characteristics of A-type granite: (1) The contents of SiO2 (70.92%-72.78%), K2O+Na2O (7.91%-8.44%) and A/CNK (0.89-0.99) are high, indicating that monzogranites are metaluminous rock and belongs to the high potassium calcium alkaline series; (2) The monzogranites are enriched in LREE (196×10-6-280×10-6) and depleted in HREE (22.8×10-6-28.2×10-6). Negative Eu anomaly is obvious, with δEu values of 0.51-0.64, and the monzogranites are characterized by fractionated chondrite-normalized REE patterns; (3) The monzogranites are enriched in Rb, Th, K and other large ion lithophile elements and depleted in Nb, Ta, Zr, P, and other high field strength elements.
      Conclusions Combined with the regional tectonic evolution, it is considered that the Tagelake monzogranites were formed in the post-collision tectonic setting.

       

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