Fractionation Of Iron Isotopes Under High Pressure: A Discussion On The Core-mantle Interaction And The Crystallization Process Of The Magma Sea

Iron,as one of the most abundant elements on the Earth,holds key information of the Earth's origin in its isotopic composition.The 0.1 per mil difference of iron isotopic composition between mid ocean ridge basalts(MORBs)and chondrites is still under debate.We applied Nuclear Resonant Inelastic X-ray Scattering technique together with high pressure diamond anvil cell to study the iron isotopic fractionation between lower mantle phases under high pressure.We found that the force constant of iron in ferropericlase is primarily controlled by spin state,the bonding of low-spin iron was significantly stiffened.The iron force constant in bridgmanite was dominated by local lattice distortion,which happens around 40-60GPa and soften the iron bonding strength.At the Core-Mantle boundary,we showed that the ferropericlase is enriched in heavy iron isotopes relative to bridgmanite and iron alloys by 0.15 and 0.12 per mil,respectively.Modelling of core mantle interaction and magma ocean crystallization showed that there is negligible iron isotopic fractionation in the two processes,which can be ruled out when seeking the origin of heavy iron isotopic composition of MORBs.