Thermal equation of state of hcp‐iron: Constraint on the density deficit of Earth's solid inner core. Issue 13 (4th July 2016)

• Record Type: Journal Article
• Authors: Fei, Yingwei; Murphy, Caitlin; Shibazaki, Yuki; Shahar, Anat; Huang, Haijun
• Is Part Of: Geophysical research letters. Volume 43:Issue 13(2016)
• Page Start: 6837
• Page End: 6843
• Publication Date: 2016-07-04
• Subjects: equation of state -- core density -- iron; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2016GL069456
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: 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 K 0 = 172.7(±1.4) GPa and its pressure derivative K 0 ′ = 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. Key Points: Intercalibrated pressure scales lead to a consistent compression curve of hcp‐iron up to 300 GPa Thermal equation of state of hcp‐iron is refined by combining static and dynamic data The inner core density deficit is 3.6% at an inner core boundary temperature of 6000 K