Measurement of melting temperatures of some minerals under lower mantle pressures

Melting temperature measurements of six minerals (stishovite (SiO 2 ), corundum(Al 2 O 3 ), diopside (CaMgSi 2 O 6 ), and three perovskites (MgSiO 3 , CaSiO 3 , Mg 3 Al 2 Si 3 O 12 )) 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 MgSiO 3 perovskite agreed with the recent measurements by Zerr and Boehler (1993) within experimental uncertainties. Melting temperatures and melting slopes of CaSiO 3 and Mg 3 Al 2 Si 3 O 12 perovskites were found to be less than those of MgSiO 3 perovskite, indicating that the presence of Ca and Al would decrease the melting temperatures of MgSiO 3 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.