Serpentine Stability to Mantle Depths and Subduction-Related Magmatism

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Abstract
Results of high-pressure experiments on samples of hydrated mantle rocks show that the serpentine mineral antigorite is stable to ∼720°C at 2 gigapascals, to ∼690°C at 3 gigapascals, and to ∼620°C at 5 gigapascals. The breakdown of antigorite to forsterite plus enstatite under these conditions produces 13 percent H 2 O by weight to depths of 150 to 200 kilometers in subduction zones. This H 2 O is in an ideal position for ascent into the hotter, overlying mantle where it can cause partial melting in the source region for calc-alkaline magmas at a depth of 100 to 130 kilometers and a temperature of ∼1300°C. The breakdown of antigorite in hydrated mantle produces an order of magnitude more H 2 O than does the dehydration of altered oceanic crust.