Abstract

The tempo of subduction-related magmatic activity over geological time is episodic. Despite intense study and their importance in crustal addition, the fundamental driver of these episodes remains unclear. We demonstrate quantitatively a first order relationship between arc magmatic activity and subduction flux. The volume of oceanic lithosphere entering the mantle is the key parameter that regulates the proportion of H2O entering the sub-arc. New estimates of subduction zone H2O budgets 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. Similar magmatic pulses in the ancient Earth could be related to variability in subduction flux associated with supercontinent cycles.