Geodynamics Research Center, Ehime University, Matsuyama 790-8577, Japan.
Science. 2010 Jan 8;327(5962):193-5. doi: 10.1126/science.1181443. Epub 2009 Dec 3.
Phase transitions and the chemical composition of minerals in Earth's interior influence geophysical interpretations of its deep structure and dynamics. A pressure-induced spin transition in olivine has been suggested to influence iron partitioning and depletion, resulting in a distinct layered structure in Earth's lower mantle. For a more realistic mantle composition (pyrolite), we observed a considerable change in the iron-magnesium partition coefficient at about 40 gigapascals that is explained by a spin transition at much lower pressures. However, only a small depletion of iron is observed in the major high-pressure phase (magnesium silicate perovskite), which may be explained by preferential retention of the iron ion Fe3+. Changes in mineral proportions or density are not associated with the change in partition coefficient. The observed density profile agrees well with seismological models, which suggests that pyrolite is a good model composition for the upper to middle parts of the lower mantle.
相转变和地球内部矿物的化学成分影响着对其深部结构和动力学的地球物理解释。橄榄石中的压力诱导自旋转变被认为会影响铁的分配和消耗，从而导致地球下地幔中出现明显的分层结构。对于更现实的地幔成分（辉橄岩），我们在大约 400 吉帕斯卡时观察到铁镁分配系数的显著变化，这可以用较低压力下的自旋转变来解释。然而，在主要的高压相（镁橄榄石钙钛矿）中仅观察到少量的铁消耗，这可能可以用铁离子 Fe3+的优先保留来解释。矿物比例或密度的变化与分配系数的变化无关。观察到的密度剖面与地震学模型吻合得很好，这表明辉橄岩是下地幔上部到中部的一个很好的模型成分。
