青藏高原壳幔结构构造的基本特征

Basic features of crust-mantle structure of the Tibet Plateau

关键词:  青藏高原  碰撞  岩石圈构造  班怒带

Key words:  Tibetan Plateau  collision  lithosphere structure  Bangonghu-Nujiang tectonic belt

摘要:

青藏高原是新生代以来由于印度板块与欧亚板块碰撞而迅速隆起，平均海拔超过4000 m的高原，是研究碰撞过程和形成演化的理想窗口。有关青藏高原的碰撞过程及印度板块岩石圈北缘界线，至今仍然存在较大争议，这可能主要是由于不同研究方法获得认识的差异性和局限性所导致。基于此，本文利用前人深部结构资料，讨论了高原岩石圈的壳幔构造及物质组成等，并从新的地质视角讨论了班怒带的大地构造属性。通过梳理前人的深部结构资料，认为青藏高原的壳幔岩石圈结构较为复杂，如高原内部岩石圈厚度显著大于周缘地区，中下地壳及上地幔广泛分布着低速高导层，这些特殊的地质地球物理结构是印亚板块碰撞的结果。此外，本文进一步对比分析了班怒带的地质与地球物理结构，揭示该构造带两侧存在显著的差异，认为其是印度岩石圈的北缘，这对于认识青藏高原的形成演化具有重要的意义。

Abstract:

The Tibet Plateau, a result of the collision between the Indian plate and the Eurasian plate since the Cenozoic, with a more than 4000 m average elevation, is an ideal site to study the collision processes. The collision processes of the Tibet Plateau and the northern boundary of the Indian plate lithosphere are still controversial, which may be caused by the differences and limitations of different research methods. The crust-mantle structure and material composition of the plateau lithosphere are discussed in this paper, and the tectonic attributes of the Bangonghu-Nujiang tectonic belt are discussed from a new geological perspective. Based on the previous deep structure data, it is concluded that the crust-mantle lithosphere structure of the Tibet Plateau is relatively complex, for example, the lithosphere thickness inner the Plateau is significantly thicker than that in the surrounding areas, and the low velocity and high conductivity layers are widely distributed in the middle and lower crust and upper mantle. These special geological and geophysical structures are the result of the Indian-Asian plate collision. In addition, the geological and geophysical structures of the Bangonghu-Nujiang tectonic belt are compared and analyzed in this paper. It is concluded that there are significant differences between the two sides of the Bangonghu-Nujiang belt, indicating that it is the northern margin of the Indian lithosphere.