Author name: Mihai N. Ducea

The world’s biggest Phanerozoic magmatic arcs formed above subduction zones and comprise the products of continuous magma emplacement into the crust over periods of up to 500 My. However, the intensity of magmatic activity can vary significantly. Punctuated magmatic events lasting from 5 to 20 My can dwarf the volume of magmas generated through the remainder of an arc’s history: these high-volume events are called “fl areups” and can completely rebuild an arc’s crust. In arcs formed on continental lithosphere, fl are-ups typically correlate with regional structural events that shorten and/or thicken the crust. Geochemical and isotopic signatures show that these high magmatic addition rate events involve ~50% recycled upperplate crust and mantle lithosphere; the remaining ~50% comes from the mantle wedge.

In this issue of Elements we explore the characteristics, potential causes, and implications of episodic magmatism in arcs. A comparison of U–Pb bedrock and detrital zircon ages in arcs with independent calculations of volumetric magma addition rates (MARs) indicates that the former nicely track the episodic temporal histories of arc magmatism but not MARs. MAR estimates indicate that 100–1000 times more magmatism is added to continental arcs during fl are-ups than during lulls and result in plutonic/volcanic ratios of >30/1. Episodic arc magmatism may result from external forcing on arc systems caused by events outside the arc and/or from internal cyclic processes driven by feedback between linked tectonic and magmatic processes within the arc. Along and across arc strike, changes and asymmetries in magmatic, tectonic, and geochemical histories provide important constraints for evaluating these poorly understood driving mechanisms.