Formation of highly evolved melts on the Precambrian Earth

在3.2 - 2.5 Ga之间，地球大陆地壳的长期演化以其性质和成分的明显变化为标志（Arndt 2013; Brown et al. 2020; Nebel et al. 2018; Palin et al. 2020），这可能反映了形成该地壳的主要地质过程的变化。然而，尽管经过数十年的重点研究，前寒武纪地球上的地质过程仍然是个谜（Cawood et al. 2006; Korenaga 2013; Nebel et al. 2018）。更深入地了解太古宙-元古代边界的地球地壳性质演化的方式和原因，对于理解行星尺度从停滞到移动的地球动力学机制转变的时间和原因至关重要（b<s:1> datard 2018; Korenaga 2013; Palin et al. 2020），毫无疑问，这将有助于正在进行的旨在探索和解释太阳系中其他岩石体演化的地外任务（Wade et al. 2017）。与太古宙-元古代过渡相关的是地质记录中锂-铯-钽（LCT）辉晶岩丰度的急剧增加——高度分化的长英质熔融产物，占全球锂的三分之一，几乎占世界上所有的Cs和Ta产量（Bradley & Mccauley 2017）。这些关键金属对于向可持续和可再生能源过渡至关重要。例如，锂是电动汽车所需的大多数电力存储解决方案的基础，也是确保向电网持续供应可再生能源的基础（欧盟委员会2020年）。此外，铯和钽都用于提高太阳能电池板的效率（European Commission 2020; Deepa et al. 2017）。尽管许多LCT伟晶岩的矿物学、地球化学和侵位年龄已经得到了很好的研究，但它们在克拉通形成背景下的构造岩浆演化却知之甚少（Bradley & Mccauley 2017; Muller et al. 2017; Stilling et al. 2006）。在这里，我建议对太古宙和元古宙地体进行岩石学研究，包括实地和实验室工作包，其中心主题是研究地壳生长过程中高度进化的长英质熔体是如何产生的。这项研究将提供(1)深远的和概念性的进展，在我们的社区思考地球的前寒武纪大陆是如何在一个可能不是由俯冲主导的构造制度中形成的，以及(2)更集中的研究，将解决当前和未来的社会经济问题，例如通过采用替代清洁能源来实现碳中和社会的愿望。

The secular evolution of Earth's continental crust is marked by a distinct change in properties and composition between 3.2 and 2.5 Ga (Arndt 2013; Brown et al. 2020; Nebel et al. 2018; Palin et al. 2020), which may reflect changes in the prevailing geological processes which generated this crust. However, despite decades of focused research, the geological processes that operated on the Precambrian Earth remain enigmatic (Cawood et al. 2006; Korenaga 2013; Nebel et al. 2018). Gaining a greater understanding of how and what caused the evolution in crustal properties on Earth at the Archean-Proterozoic boundary is essential to understand the timing and cause of planetary-scale transitions form stagnant to mobile-lid geodynamic regimes (Bédard 2018; Korenaga 2013; Palin et al. 2020), and would undoubtedly aid ongoing off-planet missions that aim to explore and interpret the evolution of other rocky bodies in our solar system (Wade et al. 2017).Associated with the Archean-Proterozoic transition is the dramatic increase in abundance of lithium-cesium-tantalum (LCT) pegmatites in the geological record - highly differentiated felsic melt products that account for one-third of global Li, and almost all of the world's Cs and Ta production (Bradley & Mccauley 2017). These critical metals are vital for transitioning towards sustainable and renewable energy sources. For example, lithium is fundamental to the majority of electrical storage solutions required for electric cars and also for ensuring a consistent supply of renewable energy to the power grid (European Commission 2020). Additionally, cesium and tantalum are both used to enhance the efficiency of solar panels (European Commission 2020; Deepa et al. 2017). Whereas the mineralogy, geochemistry, and age of emplacement of many LCT pegmatites have been well studied, their tectono-magmatic evolution within the context of the cratons in which they form is poorly understood (Bradley & Mccauley 2017; Muller et al. 2017; Stilling et al. 2006).Here, I propose to conduct a petrologically focused study of Archean and Proterozoic terranes, involving both field- and lab-based work packages, which have a central theme of investigating how highly evolved felsic melt was generated during crustal growth. This research will provide both (1) far-reaching and conceptual advances in our community's thinking of how Earth's Precambrian continents formed in a tectonic regime that was likely not dominated by subduction, as well as (2) more focused research that will address current and future socio-economic problems, such as the desire to achieve a carbon-neutral society by adopting alternative sources of clean energy.