Prof. Tomoo Katsura [University of Bayreuth, Germany]

Title: Development of ultrahigh-pressure generation using Kawai-type multi-anvil presses with carbide anvils, and its applications to mantle mineralogy

Time: 10:00 - 11:00 AM, Wednesday, August 16, 2017

Place: Conference room 410, HPSTAR (Shanghai)

Host: Huiyang Gou

Abstract

Mineralogy of the upper mantle and upper most part of the lower mantle has been studied in detail by using multi-anvil presses (MAPs). On the other hand, our knowledge about deeper parts of the lower mantle is rather limited, because conventional MAPs can generate pressures only up to 27 GPa. Expansion of the pressure range generated by MAPs is therefore desired. Significant efforts have been made for generating high pressures using MAPs with sintered diamond (SD) anvils, and generations of over 100 GPa was recently achieved. However, ultrahigh-pressure generation using MAPs with SD anvils requires too high skills and too high costs to be practical. For this reason, we attempted to generate higher pressures using carbide anvils. This technique now allows us generating pressures of 65 and 45 GPa at ambient and high temperature of 2000 K, respectively.

Using this technology, we synthesized Mg3Al2Si3O12 with the LiNbO3 structure, which formed by back-transition from the perovskite structure synthesized at a pressure of 43 GPa and a temperature of 2000 K. It is possible that LiNbO3-type Mg3Al2Si3O12 will be found in meteorite as a shock relic. We determined the maximum MgAlO2.5 contents in MgSiO3 bridgmanite as a function of pressure of 27 to 40 GPa at a temperature of 2000 K, showing that this content decreases with increasing pressure and principally becomes zero above 40 GPa [4]. Furthermore, the maximum MgAlO2.5 content decreases with increasing Al2O3 content in bridgmanite at constant pressure and temperature. These results suggest that bridgmanite has no storage capacity of water and noble gas in regions deeper than 1000 km depth in the Earth’s mantle, and also that bridgmanite becomes more viscous with increasing depth due to decrease in oxygen vacancy by MgAlO2.5 component.