Stability of chlorite in the upper mantle Available to Purchase

Stability of chlorite in the presence of orthopyroxene under upper-mantle conditions has been thermodynamically examined in the model system MgO-Al₂O₃-SiO₃-H₃O (MASH) All minerals were assumed to be pure in the MASH system. Calculation of the reaction curve took into account heat capacity (C_P), thermal expansion (αV), and isothermal compressibility (βV)If it is assumed Ihat ΔαV = ΔβV = 0, the stability of chlorite in the upper mantle is slightly pressure dependent; the upper stability curve for chlorite is located at 800 °C, 650 °C, and 500 °C, at 2.9 GPa, 4.2 GPa, and 5.0 GPa, respectively On the other hand, the assumption that ΔαV ≠ 0 and ΔβV ≠ 0 yields a more temperature-dependent curve for chlorite stability: 800 °C at 3.9 GPa and 700 °C at 5.5 GPa. The present calculation indicates that chlorite in down-dragged hydrous peridotite at the base of a mantle wedge decomposes at pressures of 3.0-3.5 GPa. Therefore, H₂O released from chlorite may play a partial role in producing magmas beneath a volcanic front that lies about 110 km above a subducted slab