鲁西花岗-绿岩区新太古代高镁质岩石及相关特征性岩石的成因及其地质意义

Apart from the outcrop of large volume of late Archean TTG series and late granitic rocks in the Luxi granite-greenstone terrane, recent investigation has also demonstrated that numerous high-Mg mafic-intermediate rocks and associated rock types (Nb-enriched basalts and high Ba-Sr granites) with a small volume occur sporadically in the area.It is well established that the petrogenesis of these specific types of rocks is distinctly different from those that are the products of normal evolution of magma and that they are generally believed to be rersulted from the crust-mantle interaction.Hence, they can record some crucial clues on the deep mantle source.Also, probing their petrogenesis will be helpful to better constrain the Neoarchean geodynamic setting and understand the mechanism of continental crustal growth and reworking during the late Neoarchean. In this project, we will crarry out a series of systematic invistigation and detailed study, including the regionally geological relationship between the high-Mg rocks and early TTG and late granitoids, determining the emplacement age and analysing their major-trace element contents and isotopic compositions. Our aims are to: 1) construct their space-time distribution and evolutionary patterns; 2) shed light on their petrogenesis and the nature of mantle source; 3) reveal the rock-forming mechanism and geodynamic setting; 4) provide insight into the machanism of the continental crustal growth and reworking during the late Neoarchean in Luxi granite-greenstone belt. In addition, the study will also make a great contribution to the petrogenesis of high-Mg rocks and other specific rock types in the world.

鲁西花岗-绿岩区除了大面积出露新太古代变形的TTG岩系和晚期的花岗岩之外，目前还发现许多零星出露的高镁质岩石及其共生的特征性岩石（富Nb玄武岩和高Ba-Sr花岗岩），这些特殊的岩石类型具有特殊的成岩机理并记录了重要的壳-幔相互作用的信息，对于理解区域新太古代构造-岩浆-变质变形作用将起到至关重要的作用。因此，本项目选择鲁西-花岗绿岩区出露较少的新太古代高镁质岩石及其共生特征性岩石开展系统的精细年代学、元素-同位素地球化学研究，确立这些岩石的时空展布特征及其与区域上大面积出露的TTG岩系的时空格架，示踪它们各自的岩浆源区属性，探讨其岩石成因及其壳-幔相互作用的机制，调查不同岩石系列之间的成因联系，从而揭示其深部构造背景和动力学机制，并进而探索这些岩石的产生对鲁西新太古代地壳生长的贡献以及地壳再造的机理。同时，这一研究也为国内外高镁质岩石相关特征性岩石的成因岩石学和成岩动力学研究积累资料。

我国华北克拉通的鲁西花岗-绿岩区作为全球典型的绿岩带之一，该区不仅保留大规模的晚太古代的TTG，也出露有不少典型现代造山带的特征性岩石组合。因此，该区是研究我国华北克拉通及全球大陆地壳形成和演化及其机制的重要场所，也是理解全球大陆地壳形成和演化的关键所在。本项目通过详细岩石岩相学及相关的矿物学，特别是元素和同位素的研究，包括中酸性岩石锆石U-Pb定年、微量元素及Hf-O同位素组成的分析，并配以全岩元素和同位素的研究，获得以下重要认识：1）该区存在一套典型的现代俯冲背景下形成的岩石组合，包括高镁埃达克质岩石、高镁闪长岩、富Nb玄武岩和高镁玄武岩等；2）全岩元素和同位素地球化学的特征显示这些岩石的形成明显与板块俯冲有关；3）中酸性岩石锆石微区Hf-O同位素的结果揭示存在大洋板片的熔融贡献；4）新太古代岩浆作用的连续性，以及不同时代埃达克质岩石的证实，说明鲁西新太古代的岩浆作用是板片俯冲作用的结果；5）板块构造可能也是全球大陆地壳增生的一种重要的机制。这一研究为更好的理解前寒武纪大陆地壳的形成和演化及其深部动力学机制提供了新的线索。