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

镁铁质-超镁铁质体在早期大陆地壳起源中的作用

• 批准号: 504307867
• 负责人: Professorin Dr. Annika Dziggel
• 金额: --
• 依托单位: Institut für Geologische Wissenschaften
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/504307867?language=en
• 关键词: role; mafic; ultramafic; bodies; origin

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.

地球最古老大陆地壳的主要成分是闪长岩-闪长岩-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形成的。然而，与TTG熔体形成有关的过程仍然存在争议，关于水在产生如此大量熔体中的作用和来源的基本问题尚未得到回答。本项目旨在更好地表征天然太古宙基性-超基性原岩部分熔融过程中的压力-温度-组成-时间（P-T - X-t）条件及其在TTG熔体生成中的作用。特别是，我们的目标是研究水在部分熔融过程中的作用和来源，以及基性-超基性原岩的成分多样性和水的有效性如何控制所产生的熔体的成分和体积。所调查的样品包括来自一系列太古宙地形的ttg和封闭的基性-超基性豆荚对，它们在地球动力学演化和年龄方面有所不同。相平衡正演模拟将用于限制部分熔化的条件和所产生的熔体的成分。这些结果将与微量元素模拟和相关TTG片麻岩的块状岩石地球化学相结合，将模拟的熔体成分与天然TTG片麻岩样品的熔体成分进行比较。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)提供有关熔体深度的进一步信息，以及iii)确定水在地壳熔化过程中的来源和作用。本研究的结果有可能对太古宙TTGs岩石成因的长期讨论做出重大贡献，也可能为它们形成的地球动力学背景提供进一步的见解。