Formation of highly evolved melts on the Precambrian Earth

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.