Determination of sound velocity - density and melting relation of iron-alloys under high pressure and high temperature conditions

2015 Fiscal Year Final Research Report

• Project/Area Number: 25800292
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Petrology/Mineralogy/Economic geology
• Research Institution: Tohoku University
• Principal Investigator: Sakamaki Tatsuya 東北大学, 理学(系)研究科(研究院), 助教 (30630769)
• Project Period (FY): 2013-04-01 – 2016-03-31
• Keywords: 地球科学 / 高圧 / 高温 / 鉄 / 地球核 / 内核 / 音速 / 密度

Outline of Final Research Achievements

Hexagonal close-packed iron (hcp-Fe) is a main component of Earth's inner core. The difference in density between hcp-Fe and the inner core in the Preliminary Reference Earth Model (PREM) shows a density deficit, which implies an existence of light elements in the core. Sound velocities then provide an important constraint on the amount and kind of light elements in the core.
This study shows the compressional sound velocity (Vp) of hcp-Fe up to 163 GPa and 3000 K using inelastic x-ray scattering from a laser-heated sample in a diamond anvil cell. The result indicates that Earth's inner core has a 4 to 5% smaller density and a 4 to 10% smaller Vp than hcp-Fe. This demonstrates that components other than Fe in Earth’s core are required to explain Earth's core density and velocity deficits compared to hcp-Fe. Hydrogen is a good candidate; thus, Earth's core may be a hidden hydrogen reservoir. In addition, silicon and sulfur are also possible candidates.

Free Research Field

高圧地球科学