HR: 0830h
AN: V31D-0958    [PDF]
TI: Pressure Dependency of Viscosities of MORB Melts
AU: * Ando, R
EM: andou_rt@ganko.tohoku.ac.jp
AF: Inst. Mineral. Petrol. and Econ.Geol., Tohoku Univ., Aoba-ku, Sendai, 980-8578 Japan
AU: Ohtani, E
EM: ohtani@mail.tains.tohoku.ac.jp
AF: Inst. Mineral. Petrol. and Econ.Geol., Tohoku Univ., Aoba-ku, Sendai, 980-8578 Japan
AU: Suzuki, A
EM: a-suzuki@mail.tains.tohoku.ac.jp
AF: Inst. Mineral. Petrol. and Econ.Geol., Tohoku Univ., Aoba-ku, Sendai, 980-8578 Japan
AU: Rubie, D C
EM: dave.rubie@uni-bayreuth.de
AF: Bayerisches Geoinstitut, University of Bayreuth, Bayerisches Geoinstitut Universit?t Bayreuth, Bayreuth, D-95440 Germany
AU: Funakoshi, K
EM: funakosi@spring8.or.jp
AF: Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Mikazuki-cho, 679-5198 Japan
AB: MORB (Mid Ocean Ridge Basalt) melt is one of the most abundant magmas observed in the surface of the Earth. Therefore, it is important to determine the physical properties of the melt at high pressure in order to discuss the eruption and transportation processes of the magmas. In the previous studies, viscosities of basaltic melts were measured by quenching falling sphere method using a piston cylinder apparatus. They showed that viscosities of the basaltic melts decrease isothermally to 2 GPa with increasing pressure. In the present study, we used the falling sphere X-ray radiography method together with the conventional quenching method in order to investigate the pressure dependence of viscosity of the basaltic melts above 2.0 GPa. Experimental conditions were from 1.5 to 4.4 GPa at 1873 K and from 3.5 to 5.2 GPa at 2023 K. Falling sphere X-ray radiography method was performed using KAWAI (MA-8) type multianvil press system installed at BL04B1 beamline at SPring-8 (SPEED1500). Cell assembly and experimental details are the same as Suzuki et al. (2002). Pt or Re sphere with a diameter of 100-150 mm were used as the falling sphere. Pressures and temperatures were determined from the equation of state of h-BN and MgO. Quenching falling sphere method was made using the KAWAI multianvil press system installed at Tohoku University. We used a diamond grain which is not the perfect sphere as the falling sphere marker. We made the correction for the shape of diamond marker by using liquid whose density and viscosity were known before the experiments. Experimental details were the same as that used by Mori et al. (2000). The viscosity of the MORB melt decreases with increasing pressure up to 3.0 GPa, which is consistent with the previous studies. However, it increases above 3.0 GPa with increasing pressure. The result shows the existence of minimum in viscosity at around 3 GPa. It implies that MORB melt moves most smoothly up to the depth of 100 km (~3 GPa) in the Earth_fs mantle and it might accumulate at the shallower depth to form the magma reservoir because of the viscosity minimum at high pressure. Reference Suzuki et al., Phys. Chem. Minerals. 29 (2002), 159-165 Mori et al., Earth Planet. Sci. Lett., 175 (2000) 87-92.
DE: 8145 Physics of magma and magma bodies
DE: 8434 Magma migration
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting