中天山构造带阿拉塔格环状杂岩体成因研究

Alatage rock mass is a special ring complex body outcropped in Cental Tianshan tectonic belt, and its characterized by the basic rocks in the core , intermediate rock in the midmost, and acid rock in the rim. From the core to the rim, the rock types include olive gabbro, hornblende gabbro, diorite, granodiorite, tonalite, porphyry granite,monzonitic granite and alkaline granite, and the magmatic enclaves also developed within the granitoid. This typical rock assemblage and spatial distribution provide an excellent approach to probe and further understand the origin, magmatic process, evolution for the ring complex body, meanwhile, they can also play a significant role in understanding the middle-Tianshan tectono-magmatic evolution. However, no enough petrology and geochemistry evidence are available up to now. The project is would like to study the different facies and their enclaves of the ring complex body in petrology, geochemistry, systematical zircon U-Pb geochronology and Sr-Nd-Pb-Hf-O isotope geochemistry. It is believed that these are the basic approach to reveal magmatic evolution, petrogenesis of the ring complex body, and the relationship between magmatism and deep crust-mantle interaction. Meanwhile, the geodynamics significances of the magmatic ring complex can be discussed combining the regional tectonic evolution.

阿拉塔格环状杂岩体出露于中天山构造带，核部基性岩类、中部中性岩类和外部酸性岩类，岩石组合从中心向外包括橄榄辉长岩、角闪辉长岩、闪长岩、花岗闪长岩、英云闪长岩、似斑状花岗岩，二长花岗岩，碱长花岗岩等，偏酸性的花岗岩类还发育岩浆成因的暗色包体；这种典型的岩石组合及其空间分布不仅可为丰富和认识环状杂岩体岩浆起源、岩浆作用和演化过程提供最佳研究对象，而且对于认识中天山构造岩浆演化具有十分重要的意义。但迄今为止尚无进一步的岩石学和地球化学等资料可用于探讨其成因。本项目拟通过野外地质、岩石学、元素和Sr-Nd-Pb-Hf-O同位素地球化学及锆石U-Pb年代学等研究深入剖析其岩相分带性、包体特征和相互的成因联系,查明其形成时代，探讨岩浆源区组成、岩浆作用过程与深部壳幔相互作用的关系，结合区域地质特征，分析环状杂岩体成因及其动力学背景。

阿拉塔格环状杂岩体出露于中天山构造带东段，核部基性岩类、中部中性岩类和外部酸性岩类，是研究环状杂岩体岩浆起源、岩浆作用和演化过程的最佳研究对象，而且对于认识中天山构造岩浆演化具有十分重要的意义。本项目通过野外地质调查、岩石学、元素地球化学和 Sr-Nd-Pb同位素地球化学及锆石 U-Pb 年代学等对三种岩类和其中的暗色包体进行研究，认为该花岗岩体形成于后碰撞环境，且为壳幔混源的岩浆多期次侵位的复合岩体，且环状花岗岩单元为壳源酸性岩浆与幔源基性岩浆混合作用的产物。同时, 根据酸性单元中二长花岗岩的形成时代为301-318Ma，形成于晚石炭世；而中性岩单元中的闪长岩的形成时代和基性岩单元中的辉长岩的形成时代均在285Ma左右，为早二叠世。综合研究认为，阿拉塔格环状杂岩体成因十分复杂，总体分为三个大的阶段：酸性岩浆侵位过程中，受到大量地壳物质的混染，大量残留体是最好的证据；而中性岩单元较为复杂的原因可能是岩浆侵位过程中不但受到早期酸性岩浆的影响，还受到同期基性岩浆的强烈改造。环状岩体的热气球式侵位受到东西向右旋剪切作用的影响。