Over the years, the redox-sensitive nature of uranium has brought some first-order constraints on the evolution of Earth’s surface: from the survival of detrital uraninite pointing to anoxic conditions in the Archean atmosphere/ocean, to U isotope variations in the sedimentary record enabling the quantification of past ocean anoxia. In principle, the redox sensitivity of U could also be leveraged in magmatic environments. Indeed, in silicate melts, U can occur in either the 4+, 5+, or 6+ valence state and information on magma oxygen fugacity (ƒO2) could be retrieved from U-bearing phases provided they can incorporate multivalent U during crystallization. In the first part of this talk, I will present how we used U XANES to probe the speciation of U in zircon grains from various localities, how we found that zircon can and do incorporate multivalent U in their structure, and how the relative proportion of U4+, 5+, and 6+ correlate with the ƒO2 of their host rocks. Having established U oxidations states in zircon as a new tracer of magma redox, in the second part of this talk I will then discuss how we applied this technique to zircon from the Jack Hills, Australia, how the cores and metamorphic rims of the investigated grains have distinct redox and trace elements systematics, and the novel constraints these results place on the nature of Hadean magmas and tectonic modes in the Hadean-Archean.