南阿尔金玉苏普阿勒克塔格花岗岩体成因及其对区域早古生代构造演化的启示

【研究目的】 玉苏普阿勒克塔格花岗岩体位于阿尔金造山带南部茫崖蛇绿混杂岩带内，主要由中粗粒似斑状黑云二长花岗岩及中细粒含斑黑云二长花岗岩组成。玉苏普阿勒克塔格岩体的形成时代、成因类型和岩浆物质来源尚不明确，制约了我们进一步认识该岩体形成的地球动力学背景以及南阿尔金造山带早古生代构造演化过程。【研究方法】 因此，本文对玉苏普阿勒克塔格岩体进行了岩石学、锆石U-Pb年代学、全岩地球化学、黑云母矿物化学及Hf同位素组成等方面的研究。【研究结果】 锆石U-Pb年代学研究结果表明该岩体中粗粒似斑状黑云二长花岗岩的锆石U-Pb加权平均年龄为451~447 Ma。结合前期工作获得该岩体中细粒含斑黑云二长花岗岩的年龄（430~423 Ma），笔者认为玉苏普阿勒克塔格花岗岩体属于早古生代岩浆活动的产物。黑云母矿物化学研究结果表明，玉苏普阿勒克塔格岩体形成于温度较低压力较高环境。根据玉苏普阿勒克塔格岩体两期花岗岩的矿物组成、全岩地球化学特征及形成的物理化学环境，认为该岩体属于I型花岗岩。Hf同位素组成研究结果表明，玉苏普阿勒克塔格岩体两期花岗岩具有相似的Hf同位素组成，暗示它们具有相似的物质来源：源岩以新生地壳的部分熔融为主，在侵位过程中经历了部分古老地壳物质的混染。【结论】 综合玉苏普阿勒克塔格花岗岩体的形成时代、成因类型、物质来源，结合区域构造演化资料，本文认为玉苏普阿勒克塔格岩体形成于与南阿尔金洋北向俯冲有关的活动大陆边缘环境。

Genesis of the Yusupualeke Tagh granitic pluton in the South Altun and its implications for the Early Paleozoic regional tectonic evolution

This paper is the result of geological survey engineering. Objective]The Yusupualeke Tagh granitic pluton is located in the Mangya ophiolitic mélange zone, South Altun orogenic belt. It mainly comprises the medium-coarse grained porphyritic biotite monzonitic granite and medium-fine grained phenocryst-bearing biotite monzonitic granite. However, their formation ages, petrogenesis, and material sources are still controversial, which restricts the understanding of the geodynamic background for the pluton and the Early Palaeozoic tectonic evolution of the South Altun orogenic belt. Methods]To determine the formation ages, petrogenesis, and material sources of the granitic pluton, we studied petrology, zircon U-Pb chronology, whole-rock geochemistry, biotite mineral chemistry, and Hf isotopic composition of the pluton in this paper. Results]Our results show that the medium- coarse grained porphyritic biotite monzonitic granite yielded weight mean ²⁰⁶Pb/²³⁸U ages of 451- 447 Ma. Combined with the formation ages (430- 423 Ma) of medium- fine grained phenocrystbearing biotite monzonitic granite in our previous study, we concluded that the Yusupualeke Tagh pluton was generated at Early Paleozoic. The study of biotite mineral chemistry indicated that the studied granitoids were formed in a low- temperature/highpressure environment. Based on the mineral composition, whole rock geochemistry, and diagenetic condition, we believed that the studied granitoids should be genetically ascribed to I-type granite. According to Hf isotopic compositions, the studied granitoids show similar Hf isotopic compositions, suggesting that they probably have similar material sources. They were mainly derived from the partial melting of the juvenile crust and mixed a small amount of ancient crust during the emplacement. Conclusions]Based on the formation age, genetic type, origin, and tectonic setting, and combined with the regional tectonic evolution, we proposed that the Yusupualeke Tagh granitic pluton was formed in an active continental margin setting related to the northward subduction of the South Altun ocean.