The Stability of Hydrous Potassic Phases in Lherzolitic Mantle—an Experimental Study to 9.5 GPa in Simplified and Natural Bulk Compositions

To investigate the pressure stability limit of phlogopite and the pressure-temperature stability field of its breakdown product K-richterite, experiments were conducted from 4.0 to 9.5 GPa and between 800°C and 1400°C in a subalkaline system K2o-Na2O-CaO-MgO-Al2O3-SiO2-H2O (KNCMASH) and in natural phlogopite and K-richterite-doped lherzolite systems. In KNCMASH, phlogopite breaks down between 6.0 and 6.5 GPa at 800°C and between 6.5 and 7.0 GPa at 1100°C to form potassic amphibole by the reaction phlogopite + clinopyroxene + orthopyroxene = K-richterite + garnet + olivine + H2O. In the natural system, the stability field of amphibole is shifted towards lower pressures by ∼0.5 GPa. The high-temperature stability limit of K-richterite in KNCMASH was located between 1300 and 1400°C at 8.0 GPa and at