HR: 1340h
AN: MR13A-0989    [Abstracts]
TI: Melting behavior of (Mg,Fe)O solid solutions at high pressure
AU: * Zhang, L
EM: lzhang@ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, DC 20015, United States
AU: Fei, Y
EM: y.fei@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, DC 20015, United States
AB: A new multi-anvil cell assembly was developed to provide stable heating up to 3473 K at pressures below 7 GPa. We have performed a series of experiments to investigate both the compositional and pressure effects on the melting behavior of (Mg,Fe)O solid solutions up to 3373 K at pressures of 3, 5 and 7 GPa in the multi-anvil apparatus. The occurrence of the partial melting is identified by the separation of FeO-rich partial melt from large MgO-rich (Mg,Fe)O crystals, with Mg-numbers (Mg*=100MgO/(MgO+FeO)) between 6 and 95 in the quenched phases. The temperature at which the partial melting of (Mg,Fe)O occurs increases slowly with increasing MgO content in the FeO-rich portion, from 2073 K for (Mg,Fe)O with Mg*=34 to 2273 K for Mg*=76 at 3 GPa, whereas the slope becomes much steeper in the MgO-rich portion, from 2773 K for Mg*=83 to 3373 K for Mg*=95. The experimental data at pressures of 3, 5 and 7 GPa indicate that the melting slope as a function of pressure is smaller in the FeO-rich portion (Mg*<75) than that in the MgO-rich portion. The melting temperature difference is ~100 K from 5 to 7 GPa in the FeO-rich portion, but this value increases to ~200 K in the MgO-rich portion, implying that MgO has a steeper melting curve than FeO end-member. The topology of the MgO-FeO system implies that our melting slope dTm/dP of MgO at zero pressure is several times higher than the value derived from previous experimental measurements of MgO melting at high pressure in a CO2 laser-heated diamond cell, but more consistent with some theoretically predicted values. Our results provide fundamental information for understanding deep melting in the Earth's interior, in particular, the presence of partial melt in the "ultralow velocity zone (ULVZ)" at the base of the lower mantle.
DE: 1025 Composition of the mantle
DE: 5134 Thermal properties
DE: 5460 Physical properties of materials
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting