Monazite solubility in hydrous silicic melts at high pressure conditions relevant to subduction zone metamorphism

摘要: Abstract Critical to any application of accessory phase stability subduction zone thermal structure and processes is knowledge the thermodynamic these minerals in different types subducted rock, their solubility presence fluids, extent which they fractionate trace element ratios interest. This study focuses on monazite, principal carrier light rare earth elements (LREE) thorium (Th) CaO-poor sediments. Relatively little known about mechanism monazite dissolution high-pressure hydrous melts (or supercritical fluids), yet allanite (the LREE Th oceanic basalts some CaO-rich sediments) has been used recently quantify slab-top temperatures (Plank, T., Cooper, L.B., Manning, C.E., 2009. Emerging geothermometers for estimating slab surface temperatures. Nature Geosci. 2, 611–615). We have studied at conditions (3 GPa, T  ≥ 800 °C) sediment-melting experiments. Experimental results highlight important role that phosphorous exerts silicic high pressure. Thermodynamically this corresponds a case where dissolves predominantly as its dissociated constituent ions (LREE 3 + PO 4 3 − ). contrast granitic low pressures (0.2 GPa) it appears dissolve associate LREEPO species, such essentially independent dissolved phosphorous. Our implications monazite-based thermometry, error introduced by not taking into account fluids can amount > 100 °C.