Novel Isotopic Insights Into Continent Evolution: tracing juvenile and reworked crust with titanium stable isotopes.

地球是太阳系中唯一一个有大陆在其表面漫游的行星。与大气层接触的大陆块的存在在整个地球历史中对地球表面的演变以及最终其可居住性发挥了关键作用。然而，目前尚不清楚是什么事件导致了这些大陆的发展。这项研究旨在回答一个关键但尚未解决的问题：大陆是如何形成的？我们将使用一种新的同位素示踪剂来进行研究，这种示踪剂对大陆地壳形成和演化过程中发生的特定化学反应敏感。大陆年龄往往集中在地球历史的特定日期，但原因尚不清楚。是因为大陆是在类似于今天海洋高原的环境中偶然形成的吗？还是因为地壳岩石在大陆碰撞期间优先保存下来？迄今为止，解决这些问题的尝试主要集中在解释大陆岩石年龄的模式或通过估计大陆地壳的组成。这些研究暗示，随着25亿至30亿年前板块构造的开始，大陆形成的机制可能已经发生了变化，但缺乏直接证据。 在这里，我们建议使用一种新的地球化学工具，专门设计的PI，直接识别的过程中所涉及的生成和改造的年轻地壳。首先，我们将确定的构造环境中的岩浆形成的年轻地壳形成的时间。现有的模型都意味着一个非常不同的作用，金红石，富钛矿物，参与岩浆生成可以追溯到通过其对钛稳定同位素组成的影响岩浆。通过测量整个地球历史上形成年轻地壳的岩浆岩，我们将确定金红石在其生成过程中所起的作用，并将其与特定的构造背景联系起来。第二，我们将直接确定大陆地壳的改造何时开始。在大陆碰撞过程中，先存大陆地壳发生改造。它影响着大陆地壳上层的组成，这可以通过测量陆源沉积物的时间来获得。这些沉积物的钛稳定同位素组成将反映幼年地壳和改造地壳的相对数量，并表明大陆碰撞的开始。因此，通过结合这两个目标，我们将了解地壳的形成和生存。总的来说，回答这些问题将为大陆地壳形成的机制提供新的证据，并将大大提高我们对地球内部发生的过程如何影响地球表面的理解。

The Earth is the only planet in the solar system having continents roaming at its surface. The presence of continental landmasses in contact with the atmosphere has played a pivotal role in the evolution of the Earth surface over the entire Earth history, and ultimately its habitability. Yet, it is currently unknown what sequence of events led to the development of these landmasses. This research aims to answer a key yet unresolved question: How did continents form? We will do so by using a novel isotopic tracer that is sensitive to specific chemical reactions occurring during the formation and evolution of continental crust.Continent ages tend to cluster around specific dates in Earth history, but the reasons for this remain unclear. Is it because continents formed episodically in environments akin to present day oceanic plateaux? Or is it because crustal rocks were preferentially preserved during episodes of continental collision? To date, attempts to solve these questions have mainly focused on explaining patterns in the ages of continental rocks or by estimating the composition of the continental crust through time. These studies hint that the mechanism of continent formation may have changed through time with the onset of plate tectonics 2.5 to 3 billion years ago, yet direct evidence for this is lacking. Here, we propose to use a novel geochemical tool, purposely designed by the PI, to directly identify the processes involved in the generation of juvenile crust and its reworking.First, we will identify the tectonic setting in which the magmas forming juvenile crust were formed through time. Existing models each imply a very different role for rutile, a Titanium-rich mineral for which involvement in magma generation can be traced through its impact on the titanium stable isotope composition of magmas. By measuring magmatic rocks forming juvenile crust throughout Earth's entire history, we will determine the role played by rutile in their generation and link it with a specific tectonic setting.Second, we will directly determine when reworking of continental crust started. Reworking of pre-existing continental crust occurs during continental collision. It affects the composition of the upper level of the continental crust, which can be accessed by measuring terrigenous sediments through time. The titanium stable isotope composition of these sediments will reflect the relative amount of juvenile and reworked crust and indicate the onset of continent collisions. Therefore by combining these two objectives we will learn about where crust is formed and survives. Overall, answering these questions will provide new evidence for the mechanisms by which continental crust formation occurs, and will greatly enhance our understanding of how processes occurring in Earth's interior have influenced Earth's surface.