Experimental evidence for silica-enriched Earth’s lower mantle with ferrous iron dominant bridgmanite
Izumi Mashino, Motohiko Murakami, Nοbuyοshi Miyajima, Sylvain Petitgirard
Abstract
Significance Iron-bearing bridgmanite is the most abundant mineral in the Earth’s interior. We overcome the experimental challenge of measuring iron-bearing materials by using Brillouin scattering techniques optimized for extreme pressure conditions in combination of diamond-anvil cell. By using such techniques, results of acoustic wave velocities in the pressure range of the entire mantle are reported here. Based on our results, we show that the greater part of the lower mantle is Fe 2+ -rich because the gradient of our model gives excellent fit to that of Preliminary Reference Earth Model for almost all the pressure range of the lower mantle with an Fe 3+ /ΣFe of 0.2. Our lower-mantle model also shows a distinctive Si-enriched composition with Mg/Si of 1.14 relative to the upper mantle.