Measurement of melting temperatures of some minerals under lower mantle pressures

Abstract

Melting temperature measurements of six minerals (stishovite (SiO2), corundum(Al2O3), diopside (CaMgSi2O6), and three perovskites (MgSiO3, CaSiO3, Mg3Al2Si3O12)) at high pressures were carried out in a YAG laser‐heated diamond anvil cell with rhenium metal as an absorber of the laser light. A polished or compressed disc of the sample was in contact with rhenium foil and heated by conduction. Melting was determined by plotting laser power/sample temperature function and looking for the thermal anomaly associated with the fusion of materials. All these solids were found to be highly refractory, requiring quite high temperatures for melting at the lower mantle pressures. The experimental melting results showed that for these minerals, melting temperatures increased with increasing pressure. Our results at low pressures are consistent with the data determined by other techniques (piston‐cylinder, multianvils). The high‐pressure melting of MgSiO3 perovskite agreed with the recent measurements by Zerr and Boehler (1993) within experimental uncertainties. Melting temperatures and melting slopes of CaSiO3 and Mg3Al2Si3O12 perovskites were found to be less than those of MgSiO3 perovskite, indicating that the presence of Ca and Al would decrease the melting temperatures of MgSiO3 perovskite in the Earth's lower mantle and that this effect will increase with increasing pressures. Melting temperature measurements on stishovite and corundum to pressures of 36 GPa and 25 GPa, respectively, are reported.

Melting phase relations in the MgSiO3–CaSiO3 system at 24 GPa

“…1 Melting temperatures of CaSiO 3 . The black line represents the melting temperatures calculated in this study, the crosses represent the experimental data by Gasparik et al (1994), the blue circles by Shen and Lazor (1995), the orange squares by Zerr et al (1997), and the dark gray dashed line represents the molecular dynamics simulation by Liu et al (2010). The gray region is the stability region of CaSiO 3 perovskite at the melting temperatures (Gasparik et al 1994) For liquids, we followed Liebske and Frost (2012) to maintain consistency.…”

Molecular dynamics modeling of stishovite

“…Stishovite melting at high pressures has been investigated with techniques such as shock temperature measurements [23] and DAC experiments [24]. It is still challenging to determine the phase diagram at high pressures from static and Fig.…”

Shock compression of quartz in the high-pressure fluid regime

“…Its phase diagram, revealed by a wide array of static [2][3][4][5][6] and dynamic [7][8][9][10] compression experiments, shows a transformation from tetrahedral to octahedral coordination with increasing pressure, although many details remain controversial [11][12][13]. The availability of several silica polymorphs at ambient pressure -in particular fused silica, quartz, cristobalite, coesite, and stishovite -in addition to porous samples has made dynamic compression experiments especially valuable since the different ambient densities allow shock Hugoniots to traverse a wide range of phase space [12,14].…”