The Mechanisms of Fluid Addition Partial Melting and Magma Ascent

Island arc magmatism is widely regarded to reflect partial melting following lowering of the peridotite solidus in the mantle wedge through addition of fluids released by dehydration reactions in the subducted altered oceanic

-100

-100

(TT) U flushed from slab -60 kyr ago

(TT) U flushed from slab -60 kyr ago

Ra flushed from slab <8 kyr ago

no Ra remaining in slab

226,

Fig. 6 Illustration of the depth distribution of progressive distillation of fluid mobile elements from the subducting slab. Labelled arrows indicate the locations of U addition, Ra addition, and the point after which no further 226Ra remains in the slab [after Turner et al. (2000)].

crust [e.g. Tatsumi et al. (1986); Davies & Bickle (1991)] and U-series isotope constraints can be used to provide independent information on the mechanisms of fluid addition, partial melting and melt ascent in the mantle wedge above island arcs.

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