Ice-VII inclusions in diamonds: Evidence for aqueous fluid in Earth’s deep mantle

Abstract

Encapsulating Earth's deep water filter Small inclusions in diamonds brought up from the mantle provide valuable clues to the mineralogy and chemistry of parts of Earth that we cannot otherwise sample. Tschauner et al. found inclusions of the high-pressure form of water called ice-VII in diamonds sourced from between 410 and 660 km depth, the part of the mantle known as the transition zone. The transition zone is a region where the stable minerals have high water storage capacity. The inclusions suggest that local aqueous pockets form at the transition zone boundary owing to the release of chemically bound water as rock cycles in and out of this region. Science , this issue p. 1136

Plume ‐Tree Structure Induced by Low‐Viscosity Layers in the Upper Mantle

“…In particular, recent geophysical observations and mineral experiments demonstrate that a global melt layer due to enriched water contents may be located at depths of 350–410 km in the upwelling mantle, which may cause the decrease in viscosity in the asthenosphere (Freitas et al, ; Tauzin et al, ; Vinnik & Farra, ). In addition, another thin weak layer beneath the mantle transition zone is proposed in the mantle radial viscosity profile (Mitrovica & Forte, ) and has a large effect on subduction stagnation (Mao & Zhong, ), possibly caused by grain size reduction (Panasyuk & Hager, ) or the presence of water (Pearson et al, ; Tschauner et al, ). Specifically, a carbonated layer at depths between 600 and 660 km was recently proposed (Sun et al, ), which may greatly decrease the solidus of minerals and produce a melt layer at the bottom of the mantle transition zone, consistent with the latest seismologic observations (Schmandt et al, ).…”

Ab initio spectroscopy and ionic conductivity of water under Earth mantle conditions

“…We used norm-conserving pseudopotentials (53) (fpmd.ucdavis.edu/ potentials/), with a plane wave basis set and kinetic energy cutoff of 85 Ry, which was increased to 220 Ry for pressure calculations. The densities of water were 1.57 g/cm 3 and 1.86 g/cm 3 , computed at 1,000 K to correspond to pressures of 11 GPa and 20 GPa, respectively. Our simulation supercell was cubic, with 64 water molecules.…”

“…For example, ice has been proposed to exist in cold, subducting tectonic slabs at 10-20 GPa, bearing large reservoirs of water with immense impact on terrestrial geochemistry (1). In addition, recent studies supported the existence of stable hydrous silicate minerals in the deep Earth (2) and of local aqueous pockets in the upper mantle (3) where water is an important medium to transport oxidized carbon (4,5). At the fundamental level, high pressure and temperature create complex changes in the bonding and structural properties of water, eventually leading to dissociation, and many of these changes remain poorly characterized.…”

Experimental Evidence for Partially Dehydrogenated ε-FeOOH

“…Although H is an influential volatile component, the budget of H in the lower mantle is still under debate [15]. Large uncertainties in the abundance are probably due to the scarcity to find natural samples derived from the deep mantle [16]. However, the number of DHPs revealed by laboratory experiments continues to grow with the development of high-pressure synchrotron-based experiments [17].…”