HR: 0830h
AN: P51B-0449    [PDF]
TI: High pressure sulfate-water system in the large icy satellites
AU: * Nakamura, R S
EM: nakamura@emerald.ganko.tohoku.ac.jp
AF: Faculty of Science, Tohoku University, Aramaki aza-Aoba, Aoba, Sendai, Miyagi, SDJ 980-8579 Japan
AB: The internal structure and composition of large icy satellites of giant planets are very important topics in planetary sciences. Based on the observed data of CI chondrite materials, it has been expected that three-quarters of the volatiles are sulfates, and 73wt.% of aqueous sulfate is magnesium sulfate MgSO$_{4}$ [Frederiksson et al. 1998]._@Recently, it has been considered that MgSO$_{4}$ is the most abundant volatiles in the icy objects. In the brine of orgueil meteorites, 97wt.% are composed of MgSO$_{4}$ and Na$_{2}$SO$_{4}$. Magnesium sulfate MgSO$_{4}$, is the most important brine in CI chondrites. We need to investigate the phase relations of the sulfate-water system up to the pressure of 5GPa to discuss the phases expected in the deep icy mantle or, ice-rock mixed core in the large icy satellites such as Callisto. Kargel(1991) suggested that the quantity of MgSO$_{4}$ in the model of icy objects is about 8-20wt.%, which is close to the eutectic composition at 0.1MPa, 17wt.% MgSO$_{4}$. Therefore, we adopted his estimation for the present starting compositions, i.e., the compositions of 0-30wt.% MgSO$_{4}$_@in the MgSO$_{4}$-H$_{2}$O system. We used a diamond anvil cell with external heating for the {\it in situ} optical observation. We used the ruby-fluorescene method [Mao et al. 1986] (the diameter of ruby grains is around 70$\mu$m) to determine the pressure. The temperature measurement was made by using the K-type thermocouple which was contacted to the steel gasket of the DAC. We generated temperatures more than 600K at high pressure by this cell. Identification of the phases was made by using the X-ray diffractometer and Raman spectroscope. We have clarified the phase equilibrium in the MgSO$_{4}$-H$_{2}$O binary system at room temperature. An eutectic point locates 14wt.% of MgSO$_{4}$ where high pressure ice (ice {\it �Y}), magnesium sulfate hepta-hydrate MgSO$_{4}$�7H$_{2}$O, and fluid coexist at 1.99GPa at the room temperature. We investigated this MgSO$_{4}$-H$_{2}$O binary system up to 600K and 5GPa with using the diamond anvil cell. At high pressure, we recognized MgSO$_{4}$�7H$_{2}$O phase and some high pressure ices (Ice{\it �Y}, Ice{\it �Z}) above 293K. Thus, we have the conclusions that a deep liquid ocean with the bottom pressure exceeding 1GPa must exist if MgSO$_{4}$ content exceeds more than 10wt.%. The sediment composed of MgSO$_{4}$�7H$_{2}$O phase might exist in the bottom of the ocean.
UR: http://www.ganko.tohoku.ac.jp/bussei/
DE: 0350 Pressure, density, and temperature
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
DE: 5410 Composition
DE: 6062 Satellites
DE: 6218 Jovian satellites
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting