Tracking the ‘fugacity path’ of mantle-derived magmas and its implications for coupling plate tectonics and atmospheric oxygenation

Plate tectonics and atmospheric cycles are directly linked. Secular evolution in the atmosphere is known to have changed the surface geochemistry of Earth, but more profound implications to recycling and mantle chemistry remain less constrained. Atmospheric oxygenation seems to have affected the composition and overall evolution of magmas through time, considering that the Great Oxidation Event occurred between 2.45 and 2.2 billion years ago and magmas became more oxidised during that period. However, the cryptic aspects of how an increasingly oxygenated atmosphere has changed mantle-derived magmas at the mineral scale remain broadly unknown. Exploring surface-mantle cycling in the early Earth and ascertaining when plate tectonics started thus requires deep investigation of crystallised magmas. In this proposal, we aim to use μ-XANES to measure the sulphur valence state in magmatic apatite inclusions hosted by zircon crystals to understand how magmas change fugacity across time.