Lessing, S, Dobson, DP, Rost, S orcid.org/0000-0003-0218-247X et al. (2 more authors) (2022) Kinetic effects on the 660 km-phase transition in mantle upstreams and seismological implications. Geophysical Journal International, 231 (2). pp. 877-893. ISSN 0956-540X
Abstract
The effects of reaction kinetics of bridgmanite and ferropericlase transforming to ringwoodite on elastic properties in upwelling mantle are investigated using data of kinetic experiments and internally self-consistent thermodynamic modelling of density and seismic velocities. The kinetic experiments show inhibited grain growth of ringwoodite. At the initiation of ringwoodite growth, bridgmanite completely transforms to a metastable pyrope-bearing garnet. Ringwoodite then gradually grows from the metastable assemblage of ferropericlase and garnet. The changes in mineralogy result in a low-velocity zone directly above the 660 km seismic discontinuity due to the lower seismic velocities and densities of ferropericlase and garnet compared to ringwoodite and bridgmanite. The modelling of the effects of reaction kinetics and its effect on seismic structure at ∼660 km depth shows more sensitivity to grain size than to temperature and upwelling rate. Modelling 1-D synthetic seismograms of PP (SS) underside reflections off the kinetically inhibited backward reaction to ringwoodite shows advanced travel times of underside reflections off ∼660 km depth of 0.2 - 0.8 s (1.2 - 1.6 s) for upwelling rates of 50 cm/yr and initial grain sizes between 5 and 20 cm due to the low-velocity zone above the 660 km discontinuity. The finite width of the low-velocity layer results in frequency-dependent behaviour of PP and SS underside reflection amplitudes, with higher amplitudes towards shorter periods. The effect on the travel times of P-to-s conversions used for receiver function is small (< 0.7 s) but the inhibited backward reaction leads to strong amplitude changes and significant waveform variations. The effects of reaction kinetics in mantle upwellings might serve as an additional means to map regions of large-scale upwellings and to constrain grain size in the lower mantle.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © The Author(s) 2022. Published by Oxford University Press on behalf of The Royal Astronomical Society. This is a pre-copyedited, author-produced PDF of an article accepted for publication in Geophysical Journal International following peer review. The version of record Stephan Lessing, David P Dobson, Sebastian Rost, Laura Cobden, Christine Thomas, Kinetic effects on the 660 km-phase transition in mantle upstreams and seismological implications, Geophysical Journal International, 2022;, ggac196, is available online at: https://doi.org/10.1093/gji/ggac196 |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst of Geophysics and Tectonics (IGT) (Leeds) |
Funding Information: | Funder Grant number NERC (Natural Environment Research Council) NE/F000898/1 |
Depositing User: | Symplectic Publications |
Date Deposited: | 09 Jun 2022 11:44 |
Last Modified: | 26 Jul 2022 01:26 |
Status: | Published |
Publisher: | Oxford University Press |
Identification Number: | 10.1093/gji/ggac196 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:187627 |