The role of mafic-ultramafic bodies in the origin of the early continental crust

地球最古老的大陆地壳的主要组成部分是英云闪长岩-奥长花岗岩-花岗闪长岩（TTG）系列的钠质岩石，它们是由不同深度的含水变质玄武岩部分熔融而形成的。然而，与TTG熔体形成的过程仍然存在争议，和水的作用和来源的基本问题，在生产这样的大量的熔体尚未回答。本项目旨在更好地表征的压力-温度-成分-时间（P-T- X-t）条件下的部分熔融的太古宙镁铁质-超镁铁质原岩和他们的作用，在TTG熔体的产生。特别是，我们的目标是调查的作用和部分熔融过程中的水的来源，以及如何组成的多样性的镁铁质-超镁铁质原岩和水的可用性控制的组成和体积的熔体生产。调查的样品包括对TTG和封闭的镁铁-超镁铁豆荚从一系列的太古代地形，不同的地球动力学演化和年龄。相平衡正演模拟将被用来约束部分熔化的条件和所产生的熔体的组成。这些结果将与微量元素建模和大块岩石地球化学相结合的相关TTG片麻岩比较模拟的熔融成分与天然TTG片麻岩样品。此外，锆石的U-Pb年代学、微量元素和氧同位素分析将用于i）整合锆石平衡TTG熔体的时间和P-T约束，ii）提供关于熔融深度的进一步信息，iii）确定水在地壳熔融期间的来源和作用。这项研究的结果有可能显着有助于长期的讨论太古代TTG岩石成因，也可能提供进一步的见解地球动力学背景（S），他们形成。

Major components of the Earth’s oldest continental crust are sodic rocks of the tonalite– trondhjemite–granodiorite (TTG) series, which formed through partial melting of hydrous metabasalts at different depths. However, the processes associated with TTG melt formation are still debated, and fundamental questions regarding the role and source of water in the production of such voluminous amounts of melts have yet to be answered.This project aims to better characterize the pressure–temperature–composition–time (P–T– X–t) conditions during partial melting of natural Archean mafic–ultramafic protoliths and their role in the generation of TTG melts. In particular, we aim to investigate the role and source of water during partial melting, and how the compositional diversity of the mafic–ultramafic protoliths and water availability control the composition and volume of the melts produced. The investigated samples comprise pairs of TTGs and enclosed mafic-ultramafic pods from a range of Archean terrains that differ in terms of their proposed geodynamic evolution and age. Phase equilibrium forward-modelling will be used to constrain the conditions of partial melting and the compositions of the melts produced. These results will be combined with trace element modelling and bulk-rock geochemistry of the associated TTG gneisses to compare the modelled melt compositions with those of the natural TTG gneiss samples. Additionally, U–Pb geochronology, trace element and oxygen isotope analysis of zircon will be used to i) integrate temporal and P–T constraints of the zircon-equilibrated TTG melt, ii) to provide further information on the depth of melting, and iii) to determine the source and the role of water during crustal melting. The results of this study have the potential to significantly contribute to the long-lasting discussion on Archean TTGs petrogenesis and may also provide further insights into the geodynamic setting(s) in which they formed.