Zircons reveal the history of fluctuations in oxidation state of crustal magmatism and supercontinent cycle.

We apply a zircon redox index to a global compilation of detrital zircons to track the variation of oxidation state, expressed as ΔFMQ, through Earth's history. Those from I-type rocks, which comprise mantle and crustal igneous protoliths, including tonalite-trondhjemite-granodiorites (TTGs), generally have a high oxidation state (ΔFMQ > 0). In contrast, zircons from igneous rocks derived from supracrustal source rocks (S-type) are commonly reduced (ΔFMQ < 0).