The thermodynamic properties of the earth's lower mantle

Chemical composition of the lower mantle inferred from the equation of state of MgSiO 3 perovskite

“…deep interior has a large uncertainty, it is estimated at this depth to be between about 1900 K and 2700 K (see, for example, Anderson & Sumino 1980;Jeanloz & Morris 1986) depending on the model. Therefore, it can be concluded that, within this temperature range, it is difficult to accommodate magnesiowiistite in as much as | of perovskite, assuming that XFe = 11%-If the temperature at this depth were better estimated, we could narrow the possibilities of the chemical composition.…”

“…As seen here, this is a mixture between 1: | and 1: | for XFe = 11%, and between pure perovskite and a 1: | mixture, but closer to the later, for XFe = 14%. The estimated temperature, according to various models, at this depth is between 2000 and 2800 K (see, for example, Anderson & Sumino 1980;Jeanloz & Morris 1986). It is clear from this figure that if the iron content in the lower mantle is 10% or less, or if it is 15% or more, it is difficult to satisfy the requirement of both temper ature gradient and absolute temperature, even though the mixing ratio of perovskite and magnesiowiistite is varied.…”

“…(K G Pa-1 ) Stacy (1977) 2445 0.997 6.41 5,91 Anderson & Sumino (1980) 2255 1.138 6.75 6.75 Brown & Shankland (1981) 2034 1 distribution would be superadiabatic while Jeanloz & Morris (1987) proposed a subadiabatic temperature profile, although no numerical values were given. It is clear from table 2 that the present estimate of the adiabatic gradient, 7T /i^s, gives the steepest geothermal gradient for the lower mantle, when it is calculated at the same temperature.…”