Magmatic flare-ups in arcs controlled by fluctuations in subduction water flux

The tempo of subduction-related magmatic activity over geological time is episodic. Despite intense study and its importance to crustal growth, the fundamental drivers of this episodicity remains unclear. We demonstrate quantitatively a first order relationship between arc flare-up events and high subduction flux. The volume of oceanic lithosphere entering the mantle is the key parameter that regulates the proportion and rate of H₂O entering the sub-arc. New estimates of subduction zone H₂O flux over the last 150 million-years indicate a three- to five-fold increase in the proportion of H₂O entering the sub-arc during the most recent global pulse of magmatism. Step changes in H₂O flux enable proportionally greater partial melting in the sub-arc mantle leading to a flare-up episode. Similar magmatic flare-ups in the ancient Earth could be related to variability in slab flux associated with supercontinent cycles.