Experimental modeling of ferropericlase formation under upper mantle conditions

铁方镁石(Mg，Fe)O是下地幔的主要物相之一。它以单一包裹体或与超高压相(如镁钙钛矿)一起出现在世界各地的钻石中。方镁铁石单独或与橄榄石一起在1大气压下也是稳定的。因此，仅含有铁方镁石包裹体的钻石也可能起源于过渡带，甚至是上地幔，以获得适当的块状岩石成分。在金刚石形成的同时，铁方镁石可能从碳酸盐熔体中析出，或通过氧化还原反应引起的俯冲碳酸盐的分解而生长。为了探索上地幔中铁镁石结晶的可能性，我们将在~6-10 Gpa和1600°C的温度下进行铁方镁石和碳硅酸盐熔体的平衡实验，实验配置为碳酸盐和金属相被橄榄石层分开。因此，氧化(Fe+1/2O2=FeO)和还原(MgCO3=MgO+C+O2)的过程将在空间上分离，并将研究铁方镁石和石墨/金刚石直接从富镁硅碳酸盐熔体中结晶的条件。实验将在FeO-MgO-CaO-SiO_2-CO_2-C系的高Mg#部分进行，目的是：(1)确定与方镁铁和橄榄石平衡的硅碳酸盐熔体的组成随压力和温度的变化；(2)通过还原硅碳酸盐熔体同时形成石墨或金刚石来模拟铁方镁矿的结晶。

Ferropericlase, (Mg, Fe)O, is one of the major phases in the lower mantle. It occurs in diamonds from a number of localities worldwide either as single inclusions or together with ultrahigh pressure phases such as Mg-Perovskite (bridgemanite). Ferropericlase on its own or together with olivine is stable even at 1 atm. Diamonds with ferropericlase inclusions alone may therefore also originate in the transition zone or even the upper mantle for appropriate bulk rock compositions. Simultaneous with diamond formation, ferropericlase may precipitate from carbonatitic melts or grow by decomposition of subducted carbonates induced by redox reactions. In order to explore the possibility of ferropericlase crystallization in the upper mantle, we will conduct equilibrium experiments involving ferropericlase and silico-carbonate melt at ~6-10 GPa and temperatures up to 1600°C. An experimental configuration will be employed where carbonate and metal phases are separated by an olivine layer. Thus, the process of oxidation (Fe+1/2O2=FeO) and reduction (MgCO3=MgO+C+O2) will be spatially separated, and conditions will be investigated where ferropericlase and graphite/diamond crystallize directly from Mg-rich silico-carbonate melt. Experiments will be conducted in the high-mg# portion of the FeO-MgO-CaO-SiO2-CO2-C system with the goals of: (1) determining the composition of silico-carbonate melt in equilibrium with ferropericlase and olivine as a function of pressure and temperature, and (2) simulating ferropericlase crystallization via reduction of silico-carbonate melt with simultaneous formation of graphite or diamond.