Scientists cannot directly observe deep into our Earth. To better understand the processes that control Earth's evolution, petrologists use the chemistry of magmas to infer properties of the mantle. This thesis centers on using magma chemistry to investigate the thermal variations throughout the mantle and the role of volatiles in both magma evolution and ore formation.

Chapter two reevaluates the assumptions behind olivine-liquid thermometry. Novel methods were devised to identify primitive magmas unaffected by olivine addition. Additionally, new constraints linking melt fraction to olivine forsterite content enabled a more precise determination of the amount of olivine addition required to correct the primitive magma for fractional crystallization. Applying these new methods, we reassessed the formation temperature of the North Atlantic Igneous Province, revealing that its temperature does not align with a plume origin.

Chapter three examines the evolution of volatiles in arc magmas by using a compilation of arc amphiboles to recreate the chlorine evolution of arc magmas. Amphibole-reconstructed chlorine contents indicate magmatic differentiation leads to an increase in chlorine concentration due to its incompatible behavior. The amphibole-reconstructed chlorine contents of arc magmas are significantly higher than values reported from melt inclusions, suggesting that melt inclusions may have trapped melts that had already lost volatiles. This observation implies that the crust might act as a filter for magma volatile contents, likely influencing the formation of ore deposits.

In Chapter four, amphiboles are once again employed, but this time to reconstruct the evolution of fluorine in arc magmas. The melts reconstructed from amphibole data indicate that fluorine is a compatible element, sequestered within arc cumulates. Compiled experimental data suggests amphibole crystallization controls the bulk fluorine evolution in arc magmas, creating fluorine poor, but water rich arc melts. We hypothesize that the subsequent melting of these arc cumulates gives rise to fluorine-rich yet water-poor melts, which serve as hosts for rare earth element deposits.