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Abstract

The formation, evolution, and long-term stability of the cratons are central to understanding how the first continents formed and how the Earth operated before the onset of modern plate tectonics. The cratonic mantle keel – the subcontinental lithospheric mantle – plays a critical role in stabilizing the continental lithosphere. However, the timing and nature of processes that shaped the SCLM remain poorly constrained due to the limited availability of geochronological tools applicable to peridotitic mantle rocks. This dissertation addresses this gap by refining and applying high-precision Lu-Hf geochronology to garnet-bearing mantle xenoliths, and by integrating Hf isotope data from tonalite-trondhjemite-granodiorite (TTG) rocks, the earliest products of continental crust formation. This work presents the first large-scale systematic application of low-dispersion internal Lu-Hf isochron dating to mantle xenoliths from the Slave, Kaapvaal, and Siberian cratons. The resulting ages spans over three billion years and demonstrate that preservation of ancient Lu-Hf ages depends on lithology, texture, and metasomatic history. A case study of a recrystallized orthopyroxenite-harzburgite xenolith reveals successive Archean metasomatic events recorded at the grain scale. Complementary TTG zircon data show globally consistent, mildly suprachondritic initial Hf isotope values, suggesting derivation from a long-lived, mildly depleted mantle reservoir. This convergence of mantle and crustal Hf signatures supports the existence of a chemically stable Archean mantle source. Beyond geodynamic implications, this dissertation introduces new methods for handling low-concentration samples and analyzing small-volume garnet separates, improving the feasibility of dating even the most refractory mantle materials. The results support a model of episodic SCLM modification, involving long-lived carbonatitic metasomatism followed by short-lived, localized hydrous overprints prior to kimberlite magmatism. These findings provide new constraints on the geodynamic processes that shaped early Earth and contribute to our broader understanding of mantle reservoirs and crust formation in the Archean.