Ultrahigh‐Pressure Acoustic Velocities of Aluminous Silicate Glass up to 155 GPa With Implications for the Structure and Dynamics of the Deep Terrestrial Magma Ocean
Pinku Saha, Motohiko Murakami, Catherine McCammon, Christian Liebske, Ewa Krymarys
Abstract
Abstract We have carried out in situ high‐pressure acoustic velocity measurements of (Fe 2+ , Al)‐bearing MgSiO 3 glass up to pressures of 155 GPa, which confirmed a distinct pressure‐induced trend change in the transverse acoustic velocity ( V S ) profile around 98 GPa, likely caused by the Si‐O coordination number (CN) change from 6 to 6 + . Although it has been reported that the substitution of Fe 2+ in MgSiO 3 glass induces almost linear velocity reduction up to ∼160 GPa, we revealed that the V S profile of (Fe 2+ , Al)‐bearing MgSiO 3 becomes anomalously steeper above ∼100 GPa and eventually came to be equivalent to MgSiO 3 glass above ∼125 GPa. This implies the incorporation of Al into Fe‐bearing MgSiO 3 glass significantly facilitates making it far elastically stiffer and thus the densification under pressures well within the Earth's lower mantle. Our results indicate the possible presence of stiff and highly dense silicate melts in deep MOs in the rocky terrestrial planets.