The onset of plate tectonics 3 billion years ago? - New insights from Ca-Sr-Pb-Nd isotopes and implications for large-scale crustal evolution

大陆地壳是过去44亿年来控制地球演化的过程和事件的档案。它的形成改变了地幔和大气的组成，支持了生命，通过风化和侵蚀仍然是二氧化碳的汇。因此，陆壳在地球的演化中发挥了关键作用，但它的生成时间和形成其演化的过程仍然是一个相当有争议的话题。随着关于地质过程的观点的演变，以及随着地层学、岩石学、古生物学、地球化学、地质年代学、地球物理学和模型学的发展，对陆壳演化的看法发生了巨大的变化。至关重要的是，随着板块构造理论的发展和接受，我们对陆壳形成和演化过程的理解在20世纪后半叶和21世纪初得到了极大的发展。一个根本的问题是确定板块构造开始的时间，最近的一些研究认为，地球演化中的这一重大变化可能发生在30亿年前的中太古代。地球演化的这一模式仍然备受争议，并受到社会各界的激烈辩论。因此，这一模型的验证是通过地幔、大陆地壳和大气之间的反复相互作用来理解地球大规模演化的关键一步。这一建议是利用一种新的地球化学方法，在分析具有不同地球化学性质和衰变常数(K-Ca、Rb-Sr、U-Pb和Sm-ND)的各种同位素体系的基础上，探索陆壳随时间的生成、成熟和生长过程。这些数据将能够确定大陆地壳在其演化不同阶段的组成，以及与俯冲有关的岩浆作用和与板内有关的岩浆作用之间的平衡随时间的变化，这一信心是迄今尚未实现的。30亿年前从与板块内有关的岩浆向与俯冲有关的岩浆的急剧转变，以及从这个时候开始的高地壳循环率，将构成此时全球板块构造开始的明确证据。

The continental crust is the archive of the processes and events that have controlled our planet's evolution for the last 4.4 billion years. Its formation modified the composition of the mantle and the atmosphere, it supports life, and it remains a sink for carbon dioxide through weathering and erosion. The continental crust has therefore had a key role in the evolution of the Earth, and yet the timing of its generation, and the processes that shaped its evolution, remain a topic of considerable debate.Views on the evolution of the continental crust have changed dramatically as ideas on geological processes have evolved and as methods to interrogate the rock record have advanced through developments in stratigraphic analysis, petrography, paleontology, geochemistry, geochronology, geophysics and modelling. Crucially our understanding of the processes involved in the generation and the evolution of the continental crust has grown enormously through the latter part of the 20th and beginning of the 21st centuries following on from the development and acceptance of plate tectonic theory.A fundamental question is to determine when plate tectonics started, and a few studies have recently argued that this major change in Earth's evolution may have happened 3 billion years ago during the Mesoarchaean. This model of Earth's evolution remains highly controversial and much debated by the community. The validation of this model is therefore a key step in understanding the large-scale evolution of the Earth, through repeated interaction between the mantle, the continental crust and the atmosphere. This proposal is to explore the processes of generation, maturation and growth of the continental crust through time, using a new geochemical approach based on the analysis of various isotopes systems with different geochemical properties and decay constants (K-Ca, Rb-Sr, U-Pb and Sm-Nd), in a large range of rocks, minerals and sediments with pre- and post-3 Ga ages. The data will allow to establish the composition of the continental crust at different stages of its evolution, as well as the variation in the balance between subduction-related and intraplate- related magmatism through time, with a confidence that has not been achieved hitherto. A sharp transition from intraplate-related to subduction-related magmas at 3 billion years ago, along with high rates of crust recycling from this time, would constitute clear evidence for the global onset of plate tectonics at this time.