Tonalite-trondhjemite-granodiorite Isotopes Tracing Archean tectoNics (TITAN)

Earth’s habitability is driven by plate tectonics. Tectonics stabilize Earth's atmosphere, recycle nutrients, and regulate temperature. However, the onset of plate tectonics remains poorly constrained. To answer this question, I plan to analyze a large suite of tonalite-trondhjemite granodiorites (TTGs) samples. TTGs are rocks that either formed as the consequence of melting basal oceanic crust, or as the product of subducting crust. I will investigate this through a unique combined isotopic approach. Titanium (Ti) isotope variations can trace primary TTG crystallization. Magnesium (Mg) isotopes fractionate by weathering, allowing differentiation of whether crust is from the surface or far beneath it. Zinc (Zn) isotope ratios provide a second proxy for weathering. Coupled differences between Zn and Mg can confirm if TTGs experienced weathering and subduction. First, I will analyze melts from the Lewisian complex (Scotland). These samples span a range of proto-TTG formation and will allow me to construct an isotopic proxy for TTG generation. Second, I will analyze a comprehensive set of well characterized and dated TTGs from multiple continents. Finally, using thermodynamic modelling software (Thermo-calc) I will construct a robust model for TTG generation. This project offers the opportunity to answer long unanswered questions about the early Earth, and provide insights to the onset of plate tectonics, the key to habitability.