MAXIMUM SOLUBILITY OF FEO IN (MG, FE)SIO3-PEROVSKITE AS A FUNCTION OFTEMPERATURE AT 26 GPA - IMPLICATION FOR FEO CONTENT IN THE LOWER MANTLE

We have explored phase relations in the fundamental ternary system MgO -FeO-SiO2 at lower mantle pressure (26 GPa) via synthesis experiments on the join MgSiO3-FeSiO3. The maximum solubility of FeO in (Mg,Fe)SiO 3 perovskite as a function of temperature has been determined in the m ultianvil apparatus in the temperature range of 1150-1740 degrees C. P ure perovskites with 10 and 15 mol % FeSiO3 can only be synthesized ab ove 1525 degrees C and 2072 degrees C, respectively, at 26 GPa. Synthe sis experiments were also conducted in a laser-heated diamond anvil ce ll to resolve a previous discrepancy concerning the maximum solubility of FeO in (Mg,Fe)SiO3 perovskite determined by different high-pressur e apparatus. Both Mossbauer spectroscopic and X my diffraction studies revealed that laser-heated samples with more than 10 mol % FeSiO3 inv ariably contained magnesiowustite. The coexistence of magnesiowustite with relatively lower FeO content perovskite results from chemical dis equilibrium process caused by the large temperature gradient in the la ser-heated samples. Finally, we conclude that the maximum FeO content at the top of the lower mantle is about 12 mol % for a perovskite-domi nated lower mantle, along a 2000-K lower mantle geotherm.