Equations of state of iron sulfide and constraints on the sulfur content of the Earth

Abstract

•S, FeS•., and Fe when constrained to the seismologically obtained density-pressure profiles of the outer core of the earth indicate a systematic decrease of apparent sulfur content from 10 to 6.5% with depth. When the shock data are reduced to isotherms, a nearly constant sulfur content in the range 9-12% is inferred. Using these bounds on the sulfur content of the core, and depending on whether an olivine or pyroxene mantle stoichiometry is assumed, the earth can be modeled as being depleted in S by a factor ranging from 1.7 to 3.2 with respect to the abundances of Si and from 2.8 to 7.5 relative to the abundance of Fe, in CCI carbonaceous chondrites. It is concluded that although th,e shock wave data permit the major light element in the core to be sulfur, the earth can be modeled as being depleted in sulfur, along with other volatile elements. A systematic relation, Co(km/s) = 7.15 -0.4712, was also discovered upon comparison of the inferred densities and bulk sound speeds (Co) of the hpp's of the iron sulfides with other measurements for 12 sulfides and elemental sulfur. Here I? is the volume (in cubic centimeters) per mole of atoms.

Phase transitions in the Mars mantle

“…Many authors think that there are two important phase transitions in the mantle of the Earth, which take place with the pressure related to the depth 420 and 670 km (e.g., (Ahrens, 1979)). Results of Ito and Takahashi (1987) showed that the second phase transformation occurs over a small pressure interval.…”

Shock Demagnetization of Pyrrhotite (Fe1−xS, x≤0.13) and Implications for the Martian Crust and Meteorites

“…The presence of monoclinic pyrrhotite was confirmed by the low temperature magnetic transition at 30-34 K [16] and the presence of hexagonal pyr-rhotite was inferred from XRD and microprobe measurements (Fe/S=0.893). Although the Hugoniot Elastic Limit of pyrrhotite is unknown, a major shockinduced phase change is observed between 2.7 and 3.8 GPa [13]. The density of the pyrrhotite was 4.587 (±100) g cm -3 , and the longitudinal and shear wave speeds are 4399 (±87) m s -1 and 2873 (±37) m s -1 respectively.…”

“…Previous shock experiments on magnetite-bearing igneous rocks [7][8][9][10][11], hematite powders [12], and pure samples of magnetite, hematite and titanohematite [4] indicate that low pressure shocks demagnetize low coercivity minerals. Previous pyrrhotite shock Hugoniot measurements did not include a magnetic study [13].…”

Equation of State

“…4.12), FeS (Ahrens, 1979), MgzSi04 (Watt and Ahrens, 1983), and CaO (Jeanloz and Ahrens, 1980) (Fig. 4.13).…”

“…In the case of calcia, the low-pressure phase is the Bl structure, mixed phase is indicated, and the high-pressure phase regime is in the B2 structure. Bancroft et al (1965), and in the case of CaO and the B1 to B2 transition discovered by leanloz and Ahrens (1979), complete reversion of the lowpressure phase occurs upon unloading. These latter transitions involve rearrangement of the lattice which can occur via its deformation rather than complete reconstruction.…”