Jiuhua Chen, Tony Yu, Shu Huang, Jennifer Girard, Xiaoyang Liu
PEPI Volume 228, March 2014, Pages 294–299
2-D brightness fitting of the Al2O3 reference sphere in the radiograph (inset) based on Beer-Lambert law to derive density of liquid FeS sample at high pressures. Blue and red symbols are experimental and calculated data, respectively.
Density of liquid FeS was measured at 1650 K and pressures up to 5.6 GPa using the X-ray absorption radiograph system of the COMPRES high pressure facility at the X17B2 beamline, NSLS. The experimental data were fitted to the third-order Birch–Murnaghan equation of state to calculate the isothermal bulk modulus (K0) of the liquid, yielding K0 = 11 ± 3 GPa when the pressure derivative of bulk modulus is fixed at 5. Combining this result with those from previous studies on Fe–S liquid system, we suggest an exponential relation between the liquid Fe–S alloy bulk modulus and its sulfur content. The exponential relation and the linear relation present a 14 GPa difference in K0 (60 GPa from the linear relation and 46 GPa from the exponential relation) at the possible liquid outer core composition, 10 wt.%S (or 16 atm% S). This is significant for the core composition modeling.
Brandon Schmandt, Steven D. Jacobsen, Thorsten W. Becker, Zhenxian Liu, Kenneth G. Dueker; Science 344, 1265-1268 doi: 10.1126/science.1253358
(A) Single-crystal of hydrous ringwoodite (blue crystal) containing 1 wt % H2O inside a diamond-anvil cell at 30 GPa. The sample was laser heated to 1600°C in several spots (orange circles) to perform direct transformation to bridgmanite and (Mg,Fe)O. Laser heating was conducted at Sector 13 (GSECARS) of the APS. (B) Synchrotron-FTIR spectra of the recovered sample were collected at beamline U2A of the NSLS. Spectrum 1 is an unheated spot, characteristic of hydrous ringwoodite. Spectra 2 and 3 from within the laser heated spots exhibit modified IR-absorption spectra in the OH region, with a broad and asymmetric band at 3400 cm-1 (characteristic of OH in quenched glass) and a sharp peak (3680 cm-1) associated with brucite. On conversion to bridgmanite plus (Mg,Fe)O, dehydration melting occurred as intergranular melt, viewed by TEM in panel C. In this study, dehydration melting was detected just beneath the mantle transition zone from P-to-S converted phases using seismic data from NSF-Earthscope, US-Array.
The high water storage capacity of minerals in Earth’s mantle transition zone (410- to 660-kilometer depth) implies the possibility of a deep H2O reservoir, which could cause dehydration melting of vertically flowing mantle. We examined the effects of downwelling from the transition zone into the lower mantle with high-pressure laboratory experiments, numerical modeling, and seismic P-to-S conversions recorded by a dense seismic array in North America. In experiments, the transition of hydrous ringwoodite to perovskite and (Mg,Fe)O produces intergranular melt. Detections of abrupt decreases in seismic velocity where downwelling mantle is inferred are consistent with partial melt below 660 kilometers. These results suggest hydration of a large region of the transition zone and that dehydration melting may act to trap H2O in the transition zone.
Posted July 2, 2014