We conducted high‐pressure experiments on hexagonal close packed iron (hcp‐Fe) in MgO, NaCl, and Ne pressure‐transmitting media and found general agreement among the experimental data at 300 K that yield the best fitted values of the bulk modulus K0 = 172.7(±1.4) GPa and its pressure derivative K0′ = 4.79(±0.05) for hcp‐Fe, using the third‐order Birch‐Murnaghan equation of state. Using the derived thermal pressures for hcp‐Fe up to 100 GPa and 1800 K and previous shockwave Hugoniot data, we developed a thermal equation of state of hcp‐Fe. The thermal equation of state of hcp‐Fe is further used to calculate the densities of iron along adiabatic geotherms to define the density deficit of the inner core, which serves as the basis for developing quantitative composition models of the Earth's inner core. We determine the density deficit at the inner core boundary to be 3.6%, assuming an inner core boundary temperature of 6000 K.

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Earth's earliest history was marked by accretion from protoplanetary materials and segregation of the core within about 35 m.y. (Kleine et al. 2002;Yin et al. 2002) and formation of the Moon by giant impact approximately 100 m.y. after the origin of the solar system. During this primary differentiation, all elements were distributed between the Fe-rich metallic phase and the silicate mantle according to their partition coefficients D i (D i = [i] metal /[i] silicate ). The net result is that the mantle is relatively depleted in those (siderophile) elements with high D i , which partitioned strongly into the core and enriched in lithophile elements with low D values. These qualitative observations are placed in context by the observation that Earth's mantle has strong compositional affinities with chondritic meteorites (Allègre et al 1995;McDonough and Sun 1995). Figure 1 shows the abundances of a large number of elements in silicate Earth compared to those in CI chondrites plotted against the temperature at which 50% of the element would condense from a gas of solar composition. Refractory lithophile elements (those which condense at highest temperature) are present in the mantle in approximately chondritic proportions, which implies that all refractory elements are present in bulk Earth (core plus mantle) in approximately chondritic proportions. In contrast, silicate Earth is depleted in volatile elements relative to CI chondrites with a decreasing relative abundance with decreasing condensation temperature. Siderophile elements are partitioned into the core and, in the case of refractory elements, their concentrations in the metal phase may be estimated by mass balance by assuming overall chondritic abundance in bulk Earth (McDonough 2003). In contrast, the abundances of volatile elements such as S, C, and Si in the core are more difficult to estimate because of the non-chondritic bulk Earth ratios of these elements. Nevertheless, plausible bounds may be placed on their concentrations, as discussed below. Mg SiAu Pd Rh,Pt Ru,Ir Re,Os P As Mo Ca, Ti,REE Zr Sc,Al W

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The iron isotopic fractionation factor between magnetite and fayalite was measured at high temperature in a piston-cylinder apparatus. For the first time, the three-isotope method [

Silicon and Mg in differentiated rocky bodies exhibit heavy isotope enrichments that have been attributed to evaporation of partially or entirely molten planetesimals. We evaluate the mechanisms of planetesimal evaporation in the early solar system and the conditions that controled attendant isotope fractionations.Energy balance at the surface of a body accreted within ~1 Myr of CAI formation and heated from within by 26 Al decay results in internal temperatures exceeding the silicate solidus, producing a transient magma ocean with a thin surface boundary layer of order < 1 meter that would be subject to foundering. Bodies that are massive enough to form magma oceans by radioisotope decay (≥ 0.1% ) can retain hot rock vapor even in the absence of ambient nebular gas. We find that a steady-state rock vapor forms within minutes to hours and results from a balance between rates of magma evaporation and atmospheric escape. Vapor pressure buildup adjacent to the surfaces of the evaporating magmas would have inevitably led to an approach to equilibrium isotope partitioning between the vapor phase and the silicate melt. Numerical simulations of this near-equilibrium evaporation process for a body with a radius of ~ 700 km yield a steady-state far-field vapor pressure of 10 -8 bar and a vapor pressure at the surface of 10 -4 bar, corresponding to 95% saturation. Approaches to equilibrium isotope fractionation between vapor and melt should have been the norm during planet formation due to the formation of steady-state rock vapor atmospheres and/or the presence of protostellar gas.We model the Si and Mg isotopic composition of bulk Earth as a consequence of accretion of planetesimals that evaporated subject to the conditions described above. The results show that the best fit to bulk Earth is for a carbonaceous chondrite-like source material with about 12% loss of Mg and 15% loss of Si resulting from near-equilibrium evaporation into the solar protostellar disk of H 2 on timescales of 10 4 to 10 5 years. .

[1] Electrical resistivity measurements of polycrystalline iron have been performed at 5, 7, and 15 GPa and in the temperature range 293-2200 K by employing a four-wired method. The kinks in electrical resistivity associated with solid iron phase transitions and the solid to liquid transition were clearly observed upon increasing temperature. Geometry corrections due to volume variations with pressure and temperature were applied to the entire data set. High pressure and temperature thermal conductivity were calculated by fitting resistivity data through the Wiedemann-Franz law. The temperature dependences of electrical resistivity and thermal conductivity for a, g, and e solid iron have been determined at highpressure conditions. Our study provides the first experimental constraint on the heat flux conducted at Mercury's outmost core, estimated to be 0.29-0.36 TW, assuming an adiabatic core. Extrapolations of our data to Martian outer core conditions yield a series of heat transport parameters (e.g., electrical resistivity, thermal conductivity, and heat flux), which are in reasonable comparison with various geophysical estimates. Citation: Deng, L., C. Seagle, Y. Fei, and A. Shahar (2013), High pressure and temperature electrical resistivity of iron and implications for planetary cores, Geophys.

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