At a subduction zone, one plate of oceanic lithosphere dives under another plate, which ‘dewaters’ to plate (blue arrows) into the overlying mantle wedge and produces arc volcanism at the surface. Part of the hydrated mantle wedge frees itself and mixes into surrounding depleted mantle. From Widom, Nature 443, 516-517 (2006).
One element that is particularly important for her studies is lithium (Li). Dr. Tian described how Li is thought to behave chemically within the mantle in a way that allows her to trace the subduction of material into the mantle and show that it is later erupted at a mid-ocean ridge (illustrated at right).