Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session C5: GP1: Geophysics I |
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Chair: Jing-Yen Chen, Lawrence Livermore National Laboratory Room: Cascade I |
Monday, July 8, 2013 11:00AM - 11:30AM |
C5.00001: Phase relations of Earth's core materials Invited Speaker: Tetsuya Komabayashi Knowledge of thermodynamic state of the Earth's core is of primary importance for understanding the evolution of the solid Earth. In addition to iron which is its major component, several amounts of nickel and light element(s) should also be present in the core. I will review phase relations of these systems from recent high-pressure (P) and --temperature (T) experiments and thermodynamic modeling. First, I will introduce recent technical development of the so-called resistive internally heated diamond anvil cell (DAC) experiments in which thin iron (alloy) foil serves as a heater and a sample simultaneously. By resistance heating, it produces much more stable heating than the laser-heating technique and much higher temperature than the external-heating system. With this technique we conducted high-P-T in-situ measurements of the gamma-epsilon transitions in Fe and Fe-Ni alloy. In addition, I will also present new data of phase relations of Fe-Si alloy for which consistent phase relations have not been established so far. Next, thermodynamics of the core materials will be discussed based on the latest static high-P-T experiments. I constructed a thermodynamic model of melting relations in the system Fe-FeO to the outer core-inner core boundary (ICB) pressure. At the ICB pressure, calculations assuming the ideal solution for liquids show that the eutectic temperatures are much lower than results of DAC experiments showing a solid assemblage Fe$+$FeO at the same P-T conditions. Then, non-ideality of mixing for liquids was assessed to make the eutectic temperature consistent with the experiments. With the new solution model, the eutectic compositions under the core pressures are calculated. From the Gibbs free energy for the Fe-FeO liquids, I calculate the density, sound velocity, and adiabatic temperature profile of a hypothetical oxygen-bearing outer core. On the basis of these results, I will discuss if oxygen can be a major light element in the core or not. [Preview Abstract] |
Monday, July 8, 2013 11:30AM - 11:45AM |
C5.00002: Gas recovery experiments to determine the degree of shock-induced devolatilization of calcite Sohsuke Ohno, Ko Ishibashi, Toshimori Sekine, Kosuke Kurosawa, Takamichi Kobayashi, Seiji Sugita, Takafumi Matsui Shock-induced devolatilization of volatile-bearing minerals has played important roles in formation of the atmosphere and the evolution of surface environments of terrestrial planets. The dependence of the degree of devolatilization on the ambient pressure have not detailedly investigated before, although the ambient pressure must dramatically change the degree of devolatilization. In this study, we conducted shock-recovery experiments of calcite (CaCO3) using newly designed sample containers for released gas analysis and assess the dependence of the degree of devolatilization on the ambient pressure. The results clearly shows that the degree of devolatilization increases as the sample container volume increases and the initial mass of calcite decreases. [Preview Abstract] |
Monday, July 8, 2013 11:45AM - 12:00PM |
C5.00003: Electrical Resistivity of natural Marcasite at High-pressures Gopalakrishnarao Parthasarathy Marcasite is considered to be a common iron sulfide in reducing Martian sediments and may enclose microbial remains during growth and hence study of marcasite may have significance in the search for fossil life on Mars. The high-pressure phase stability investigations of marcasite are useful in understanding the sulfide mineralogy of Martian surface, affected by meteorite impacts. The sulfides were characterized by electron microprobe micro analyses (EPMA), powder X-ray diffraction, DTA, and FTIR spectroscopic measurements. The samples were powdered using a porcelain mortar and pestle. The chemical composition of the sample was determined by an electron probe micro-analyzer (EPMA). High-pressure electrical resistivity measurements were carried out on natural marcasite, and marcasite rich samples (Marcasite 95 mol {\%} pyrite 5 mol {\%}) up to 7 GPa. Marcasite sample shows a discontinuous decrease in the electrical resistivity at 5. 2 ($\pm$ 0.5) GPa indicating a first order phase transition. The Differential thermal analyses and the Fourier transform infrared spectroscopic measurements on the pressure quenched sample shows the characteristics of pyrite, indicating the pressure induced marcasite-to --pyrite transition of the natural marcasite at 5. 2 ($\pm$ 0.5) GPa. The observation of marcasite to pyrite phase transition may be useful in estimating the pressure experienced by shock events on the Martian surface as well as the meteorites where marcasite- pyrite phases coexist. [Preview Abstract] |
Monday, July 8, 2013 12:00PM - 12:30PM |
C5.00004: On the Composition and Temperature of the Terrestrial Planetary Core Invited Speaker: Yingwei Fei The existence of liquid cores of terrestrial planets such as the Earth, Mar, and Mercury has been supported by various observation. The liquid state of the core provides a unique opportunity for us to estimate the temperature of the core if we know the melting temperature of the core materials at core pressure. Dynamic compression by shock wave, laser-heating in diamond-anvil cell, and resistance-heating in the multi-anvil device can melt core materials over a wide pressure range. There have been significant advances in both dynamic and static experimental techniques and characterization tool. In this tal, I will review some of the recent advances and results relevant to the composition and thermal state of the terrestrial core. I will also present new development to analyze the quenched samples recovered from laser-heating diamond-anvil cell experiments using combination of focused ion beam milling, high-resolution SEM imaging, and quantitative chemical analysi. With precision milling of the laser-heating spo, the melting point and element partitioning between solid and liquid can be precisely determined. It is also possible to re-construct 3D image of the laser-heating spot at multi-megabar pressures to better constrain melting point and understanding melting process. The new techniques allow us to extend precise measurements of melting relations to core pressures, providing better constraint on the temperature of the cor. [Preview Abstract] |
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