ELASTIC · The effect of Fe, Al and Ti on the density, elasticity and the post-stishovite transition of eclogitic H2O-bearing stishovite: Implications on the observability of seismic anomalies in Earth’s mantle
Horizon 2020 — Marie Skłodowska-Curie Actions
- Duration
- 2020-09-01 → 2024-05-31
- EU contribution
- €295,062
- Participants
- 1
- Scheme
- MSCA-IF
Lines connect the coordinator with its partners.
Results in brief
The effect of Fe, Al and Ti on the density, elasticity and the post-stishovite transition of eclogitic H2O-bearing stishovite: Implications on the observability of seismic anomalies in Earth’s mantle
ELASTIC is aimed at determining the effect of incorporating typical eclogitic defects (Al, Ti, Fe, OH) on the high-pressure-temperature phase diagram, density, structure and elasticity of defective stishovite. To this end, a series of in situ high pressure, high temperature ultrasonic runs with various defective stishovites have been conducted. These cover geologically relevant pressure and temperature conditions near the anticipated transition (see figure). The combination of a high-density of diffraction and ultrasonic data has enabled the rutile-CaCl2 phase transition to be located precisely and evaluated across a wide range of high-pressure and high-temperature conditions. This study provides directly measured density and sound velocity measurements and thus, enables better experimental constraints of bulk elastic properties and their pressure and temperature derivatives of eclogitic stishovite at mantle-relevant pressure and temperature conditions. This study extends information essential to the interpretation of the seismic observables, and contributes to more complete modelling of subducted oceanic crustal material inside the Earth’s deep mantle. The results allow improvements to fundamental models used to predict and determine seismic anomalies caused by recycled subducted material through the Earth's mantle, particularly in the upper part of the lower mantle.
Data: CORDIS, © European Union
Project objective
Al-bearing stishovite is considered to be the main H2O-bearing silicate phase present in recycled subducted oceanic crust (i.e. eclogite) at uppermost lower mantle conditions, equivalent to >660 km mantle depths, and pressures above 23 GPa, where it can form 25% of the bulk. The incorporation of Al into stishovite leads to significant changes to its phase diagram and its ability to take up H2O. For instance, it halves the pressure required for its rutile- to CaCl2-type transformation, which exhibits significant elastic softening and may be seismically observable. We currently lack any information on the influence of Fe and Ti on the elastic properties and post-stishovite transitions of Al-and/or H2O-bearing stishovite - even though we know that these defects and solid-solutions are important features of other silicate phases in the mantle; e.g. Ca(Si,Ti)O3 perovskite. We propose a comprehensive synthesis programme, combined with on-line elastic measurements by ultrasonic interferometry and x-ray diffraction to determine the effects of defect type and concentration on the density, phase diagram and elastic response of this important suite of stishovites. This work, based at ID06LVP, The European Synchrotron, will be supplemented by examination by microscopic and spectroscopic methods at the forefront of microbeam techniques. Understanding elastic properties of Fe-, Al-, Ti-, and H2O -bearing eclogitic stishovite will allow improvements in fundamental models used to predict and determine the observability of seismic discontinuities and velocity anomalies caused by the subduction of eclogitic material through the Earth’s mantle, particularly in the upper part of the lower mantle. This study will also help to better assess the effects of incorporation of minor amounts of FeO, Fe2O3, Al2O3 and H2O in stishovite on the lower mantle’s density.
Original text from CORDIS.
Participants
- EUROPEAN SYNCHROTRON RADIATION FACILITY · GrenobleCoordinatorFrance
Links
Data: CORDIS, © European Union