CaSiO3 perovskite in diamond indicates the recycling of oceanic crust into the lower mantle

Abstract

Laboratory experiments and seismology have created a clear picture of the major minerals

Evidence for the charge disproportionation of iron in extraterrestrial bridgmanite

“…High-pressure experiments on lower-mantle compositions suggest that the mineralogy of the lower mantle is dominated by bridgmanite (1) with smaller fractions of Fe-bearing periclase and CaSiO 3 perovskite (2). However, unlike the shallower regions of the mantle, it has been difficult to obtain direct sample representatives of the lower mantle.…”

Ferropericlase Control of Lower Mantle Rheology: Impact of Phase Morphology

“…It has been suggested that the rheology of the Earth's lower mantle is governed by the rheology of its two main constituents bridgmanite and ferropericlase; however, both rheologies are not very well known at lower mantle conditions and are subject of active research (e.g., Girard et al, 2016;Immoor et al, 2018;Kaercher et al, 2016;Merkel et al, 2003;Miyagi & Wenk, 2016;Reali et al, 2019). The rheology of calcium silicate perovskite is even less known due to experimental difficulties (Miyagi et al, 2009;Nestola et al, 2018). It has been argued that due to the absence of seismic anisotropy, the lower mantle should be deforming in diffusion creep (Karato & Li, 1992).…”

Deep Carbon

“…Application of these methods has yielded the whole range of depths from 110 to 150 km, corresponding to the graphite-diamond boundary in the lithosphere, to over 660 km, lying within the lower mantle. 14,[22][23][24][25] Thus, these studies have provided direct evidence for the recycling of surficial carbon to lower-mantle depths. Traditional geobarometric methods, however, have several limitations: they can only be applied to rare types of mineral inclusions; touching inclusions may re-equilibrate after diamond growth; non-touching inclusions may be incorporated under different conditions and may not be in equilibrium; and protogenetic inclusions 26,27 may not re-equilibrate completely during diamond growth.…”

“…Since the discovery of super-deep diamonds, 18 their immense value in providing samples of the upper mantle, transition zone, and lower mantle has become clear. 24,25,98,[113][114][115] Several studies discovered olivine inclusions suggested to have previously been wadsleyite or ringwoodite based on frequent spinel exsolutions 116 or their coexistence with other phases thought to be from the transition zone. 18,117,118 During the DMGC consortium initiative on super-deep diamonds, a diamond from the Rio Aripuanã in the Juína district of Mato Grosso, Brazil, was found to contain the first terrestrial occurrence of un-retrogressed ringwoodite ( Figure 5 120 This constraint is strong evidence that the host environment for the ringwoodite was a subducted slab carrying significant H 2 O into the transition zone.…”

“…The second most abundant inclusion, after the metallic Fe-Ni-C-S, is a mix of calcium silicates interpreted as retrogressed CaSiO 3 -perovskite (CaPv), which is a high-pressure mineral stable at depths beyond about 360 km. 25,31,195 An additional inclusion phase found was low-Cr majoritic garnet, which provides a maximum depth bracket, since it is not stable deeper than about 750 km. 196 Silicate inclusion phases therefore bracket the depth to 360-750 km, overlapping the mantle transition zone.…”