Stability fields of Mg‐pumpellyite composition at high pressures and temperatures

Mg‐pumpellyite was observed to break down to the assemblage pyrope + kyanite + coesite + (H2O) in the pressure range 60–80 kbar, to the assemblage pyrope + kyanite + stishovite + (H2O) in the range 100–140 kbar, and to the asemblage pyrope + corundum + stishovite + (H2O) in the range 160–220 kbar at 800–1000°C in a diamond‐anvil cell coupled with laser heating. Mg‐pumpellyite may exist in the coldest part of a subducting lithosphere down to a depth of about 300 km.