下地幔温压条件下碳对（Mg,Fe）SiO3布里奇曼石的影响

Effects of Carbon on（Mg,Fe）SiO3 Bridgmanite under the Lower Mantle Pressure-Temperature Conditions

利用激光加温金刚石对顶砧技术模拟下地幔温压条件(36~88 GPa,1850~2800 K),探索了碳与含铁的(Mg,Fe)SiO3布里奇曼石的相互作用过程。同步辐射X射线衍射实验表明,(Mg,Fe)SiO3布里奇曼石与碳在大于42 GPa、2000 K的温压条件下发生了氧化还原反应,即(Mg,Fe)SiO3布里奇曼石中的二价铁(Fe^2+)被单质碳还原成金属铁(Fe^0);而在较低的温压条件下,布里奇曼石中的Fe2+可以稳定存在。该结果表明,在下地幔深部的温压条件下,CCO缓冲的氧逸度值比IW缓冲更低,热力学计算结果也证实了这一结果。实验结果为地幔深部氧化还原条件的不均一性和局部极端还原状态的出现提供了解释。

In this study we investigated the interaction of carbon with iron in the(Mg,Fe)SiO3 bridgmanite under the conditions corresponding to the Earth’s lower mantle(36–88 GPa,1850–2800 K)using a laserheated diamond anvil cell.Synchrotron X-ray diffraction measurements of the run products showed that Fe^2+in bridgmanite can be reduced to metallic Fe by carbon under the pressure and temperature conditions higher than 42 GPa and 2000 K.The coexisting metallic Fe and Fe-depleted bridgmanite in the run products suggests that the CCO buffer produces lower oxygen fugacity than the of Fe-Fe^O(IW)buffer,which is further confirmed by the thermodynamic calculation.The experimental results in this study could provide a potential explanation for the presence of redox heterogeneities and highly reducing regions in the deep mantle.