中条山东部～2.5Ga两类TTG的Li-Mo同位素特征及地质意义

华北克拉通最重要的构造-热事件发生在新太古代晚期，形成了大量以～2.5Ga TTG为主的岩浆岩，它是探究太古宙-元古宙过渡期大陆地壳形成机制与演化轨迹的天然实验室。这些TTG的地球化学特征具有明显差异，它们的成因存在着不同认识，争论的焦点在于源区是否存在俯冲洋壳及其贡献程度。本项目拟以中条山东部分别具有较高与较低Mg#和Cr、Ni含量的两类TTG为对象，通过野外地质调查和SIMS锆石U-Pb定年，厘清两类岩石的空间分布规律与形成时序；在锆石Hf-O与磷灰石Sr-Nd原位同位素研究基础上，基于Li-Mo同位素在示踪俯冲带物质再循环与壳幔相互作用方面的独特优势开展系统研究，揭示俯冲洋壳物质对两类TTG形成的贡献，进而约束两类岩石形成的地球动力学背景。本项目的实施不仅能为限定华北克拉通南缘～2.5Ga岩浆活动的性质提供新的约束，还能为探究太古宙-元古宙过渡期构造体制转变提供新的科学素材。

The major tectono-thermal event of the North China Craton occurred at the end of the Archean (ca. 2.5 Ga), during which a large amount of TTG-dominated igneous rocks formed. These rocks are critical for unraveling the formation and evolution of the continental crust. TTG of this period show diversity in geochemical compositions and their petrogenesis is still controversial. The key point of the controversy is about the contribution of the subducted slab to the formation of these TTG. This proposal focuses on petrogenesis of the two types of TTG in the eastern Zhongtiao region, which have high and low Mg# values, and Cr and Ni contents, respectively. Field investigation and SIMS zircon dating will be conducted to investigate their spatial and temporal distribution. Especially, Li-Mo isotope studies, associated with in-situ zircon Hf-O and apatite Sr-Nd isotopic analyses, will be applied to evaluate the influence of the subducted slab for formation of the two types of TTG. Integrated studies and comparison with regional ca. 2.5 Ga magmatism will be conducted to interpret the geodynamic setting for formation of the two types of TTG. This proposal is prospected not only to decipher the nature of the ca. 2.5 Ga magmatism in the southern NCC, but also to provide a special insight into the geodynamic transition during this period.