Hydrogen and Sulfur in Metallic Iron at High Pressure and High Temperature and Implications for the Cores of Earth and Mars
Abstract
In order to explain the density deficit [1], the Earth's core should contain a significant amount of light elements in its Fe-Ni composition. Si, S, O, C and H have been proposed as candidates given their abundance and siderophile character at the P-T conditions of core formation [1]. For Mars' core, sulfur is a primary candidate because of the large amounts found in SNC meteorites [2]. Also, the martian core is in direct contact with ringwoodite which can store a large amount of OH [3]. Because of strong partitioning of H into metallic Fe at high pressure, core hydrogenation is feasible for Mars [4]. Here, we report the first experimental study investigating metallic iron together with both sulfur and hydrogen.
We loaded foils of FeS together with compressed pure hydrogen in diamond-anvil cells. We then performed pulsed laser-heated diamond anvil cell experiments at the 13IDD beamline of the Advanced Photon Source. The newly developed pulsed laser heating enable us to reach 1800 K for the samples with a hydrogen medium. We acquired X-ray diffraction data at in situ high pressure and high temperature to identify the crystal structure of the FeS-Hx alloys. We found that the unit cell of the FeS(VI) orthorhombic structure is on the order of 20% higher than that of hydrogen-free FeS at 50 GPa, indicating a large amount of H dissolved in FeS. Hydrogen appears to expand the stability field of the FeS(VI) structure to pressures as low as 10 GPa, whereas in the H-free system the monoclinic FeS(III) structure is known to be stable at the condition [5]. Our study suggests that hydrogen can dissolve in FeS with a large amount and change the phase behaviors. If the early Mars mantle contained a significant amount of H2O, it will loose water to the core and hydrogenate the core. Hydrogen will reduce the melting temperature of the S rich Fe alloy in the martian core, affecting the geodynamo and convection in the region. [1] Poirier J P. Physics of the earth and planetary interiors, 85(3-4):319-337, 1994. [2] Stevenson D J. Nature, 412(6843):214, 2001. [3] Pearson D, et al. Nature, 507(7491):221, 2014. [4] Shibazaki Y, et al. Earth and Planetary Science Letters, 287(3-4):463-470, 2009. [5] Ono S and Kikegawa T. American Mineralogist, 91(11-12):1941-1944, 2006.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMDI43C0031P
- Keywords:
-
- 3914 Electrical properties;
- MINERAL PHYSICSDE: 3619 Magma genesis and partial melting;
- MINERALOGY AND PETROLOGYDE: 5724 Interiors;
- PLANETARY SCIENCES: FLUID PLANETSDE: 8147 Planetary interiors;
- TECTONOPHYSICS