Hydrous silicate melts and the deep mantle H2O cycle

James W.E. Drewitt; Michael J. Walter; John P. Brodholt; Joshua M.R. Muir; Oliver T. Lord

doi:10.1016/j.epsl.2022.117408

Hydrous silicate melts and the deep mantle H2O cycle

James W.E. Drewitt^*, Michael J. Walter, John P. Brodholt, Joshua M.R. Muir, Oliver T. Lord

^*Corresponding author for this work

Research output: Contribution to journal › Article (Academic Journal) › peer-review

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Abstract

We report ab initio atomistic simulations of hydrous silicate melts under deep upper mantle to shallow lower mantle conditions and use them to parameterise density and viscosity across the ternary system MgO-SiO2-H2O (MSH). On the basis of phase relations in the MSH system, primary hydrous partial melts of the mantle have 40-50 mol% H2O. Our results show that these melts will be positively buoyant at the upper and lower boundaries of the mantle transition zone except in very iron-rich compositions, where ≳ 75% Mg is substituted by Fe. Hydrous partial melts will also be highly inviscid. Our results indicate that if melting occurs when wadsleyite transforms to olivine at 410 km, melts will be buoyant and ponding of melts is unexpected. Box models of mantle circulation incorporating the upward mobility of partial melts above and below the transition zone suggest that the upper mantle becomes efficiently hydrated at the expense of the transition zone such that large differences in H2O concentration between the upper mantle, transition zone and lower mantle are difficult to maintain on timescales of mantle recycling. The MORB source mantle with ∼0.02-0.04 wt% H2O may be indicative of the H2O content of the transition zone and lower mantle, resulting in a bulk mantle H2O content of the order 0.5 to 1 ocean mass, which is consistent with geochemical constraints and estimates of subduction ingassing.

Original language	English
Article number	117408
Journal	Earth and Planetary Science Letters
Volume	581
Early online date	11 Feb 2022
DOIs	https://doi.org/10.1016/j.epsl.2022.117408
Publication status	Published - 1 Mar 2022

Bibliographical note

Funding Information:
This work used the ARCHER UK National Supercomputing Service ( http://www.archer.ac.uk ) and was supported by NERC grant NE/P002951/1 . OTL would like to acknowledge support from the Royal Society in the form of a University Research Fellowship ( UF150057 ). We are grateful to Louis Hennet (CEMHTI, Orléans) and Daniel Neuville (IPGP, Paris) for their assistance in collecting the synchrotron x-ray diffraction measurements of the levitated En and Fo melts at beamline ID11, ESRF (proposal No. HD517) (Fig. S2) and thank Marisa Wood and Yunguo Li for useful discussions on VASP. We would also like to thank Peter van Keken for his useful insights during the development of the box models.

Funding Information:
This work used the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk) and was supported by NERC grant NE/P002951/1. OTL would like to acknowledge support from the Royal Society in the form of a University Research Fellowship (UF150057). We are grateful to Louis Hennet (CEMHTI, Orl?ans) and Daniel Neuville (IPGP, Paris) for their assistance in collecting the synchrotron x-ray diffraction measurements of the levitated En and Fo melts at beamline ID11, ESRF (proposal No. HD517) (Fig. S2) and thank Marisa Wood and Yunguo Li for useful discussions on VASP. We would also like to thank Peter van Keken for his useful insights during the development of the box models.

Publisher Copyright:
© 2022 The Author(s)

Research Groups and Themes

PetrologyGroup
PetrologyLabs

Keywords

hydrous melts
density
viscosity
transition zone
molecular dynamics
mantle H2O cycle

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Ab initio Molecular Dynamics Trajectories for Hydrous Silicate Melts
Drewitt, J. W. E. (Creator), NERC, 28 Sept 2022
DOI: 10.5285/c61af45c-8386-4c1a-83ee-61a769843dc2, https://www2.bgs.ac.uk/nationalgeosciencedatacentre/citedData/catalogue/c61af45c-8386-4c1a-83ee-61a769843dc2.html
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Cite this

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title = "Hydrous silicate melts and the deep mantle H2O cycle",

abstract = "We report ab initio atomistic simulations of hydrous silicate melts under deep upper mantle to shallow lower mantle conditions and use them to parameterise density and viscosity across the ternary system MgO-SiO2-H2O (MSH). On the basis of phase relations in the MSH system, primary hydrous partial melts of the mantle have 40-50 mol% H2O. Our results show that these melts will be positively buoyant at the upper and lower boundaries of the mantle transition zone except in very iron-rich compositions, where ≳ 75% Mg is substituted by Fe. Hydrous partial melts will also be highly inviscid. Our results indicate that if melting occurs when wadsleyite transforms to olivine at 410 km, melts will be buoyant and ponding of melts is unexpected. Box models of mantle circulation incorporating the upward mobility of partial melts above and below the transition zone suggest that the upper mantle becomes efficiently hydrated at the expense of the transition zone such that large differences in H2O concentration between the upper mantle, transition zone and lower mantle are difficult to maintain on timescales of mantle recycling. The MORB source mantle with ∼0.02-0.04 wt% H2O may be indicative of the H2O content of the transition zone and lower mantle, resulting in a bulk mantle H2O content of the order 0.5 to 1 ocean mass, which is consistent with geochemical constraints and estimates of subduction ingassing.",

keywords = "hydrous melts, density, viscosity, transition zone, molecular dynamics, mantle H2O cycle",

author = "Drewitt, {James W.E.} and Walter, {Michael J.} and Brodholt, {John P.} and Muir, {Joshua M.R.} and Lord, {Oliver T.}",

note = "Funding Information: This work used the ARCHER UK National Supercomputing Service ( http://www.archer.ac.uk ) and was supported by NERC grant NE/P002951/1 . OTL would like to acknowledge support from the Royal Society in the form of a University Research Fellowship ( UF150057 ). We are grateful to Louis Hennet (CEMHTI, Orl{\'e}ans) and Daniel Neuville (IPGP, Paris) for their assistance in collecting the synchrotron x-ray diffraction measurements of the levitated En and Fo melts at beamline ID11, ESRF (proposal No. HD517) (Fig. S2) and thank Marisa Wood and Yunguo Li for useful discussions on VASP. We would also like to thank Peter van Keken for his useful insights during the development of the box models. Funding Information: This work used the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk) and was supported by NERC grant NE/P002951/1. OTL would like to acknowledge support from the Royal Society in the form of a University Research Fellowship (UF150057). We are grateful to Louis Hennet (CEMHTI, Orl?ans) and Daniel Neuville (IPGP, Paris) for their assistance in collecting the synchrotron x-ray diffraction measurements of the levitated En and Fo melts at beamline ID11, ESRF (proposal No. HD517) (Fig. S2) and thank Marisa Wood and Yunguo Li for useful discussions on VASP. We would also like to thank Peter van Keken for his useful insights during the development of the box models. Publisher Copyright: {\textcopyright} 2022 The Author(s)",

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doi = "10.1016/j.epsl.2022.117408",

language = "English",

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AU - Drewitt, James W.E.

AU - Walter, Michael J.

AU - Brodholt, John P.

AU - Muir, Joshua M.R.

AU - Lord, Oliver T.

N1 - Funding Information: This work used the ARCHER UK National Supercomputing Service ( http://www.archer.ac.uk ) and was supported by NERC grant NE/P002951/1 . OTL would like to acknowledge support from the Royal Society in the form of a University Research Fellowship ( UF150057 ). We are grateful to Louis Hennet (CEMHTI, Orléans) and Daniel Neuville (IPGP, Paris) for their assistance in collecting the synchrotron x-ray diffraction measurements of the levitated En and Fo melts at beamline ID11, ESRF (proposal No. HD517) (Fig. S2) and thank Marisa Wood and Yunguo Li for useful discussions on VASP. We would also like to thank Peter van Keken for his useful insights during the development of the box models. Funding Information: This work used the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk) and was supported by NERC grant NE/P002951/1. OTL would like to acknowledge support from the Royal Society in the form of a University Research Fellowship (UF150057). We are grateful to Louis Hennet (CEMHTI, Orl?ans) and Daniel Neuville (IPGP, Paris) for their assistance in collecting the synchrotron x-ray diffraction measurements of the levitated En and Fo melts at beamline ID11, ESRF (proposal No. HD517) (Fig. S2) and thank Marisa Wood and Yunguo Li for useful discussions on VASP. We would also like to thank Peter van Keken for his useful insights during the development of the box models. Publisher Copyright: © 2022 The Author(s)

PY - 2022/3/1

Y1 - 2022/3/1

N2 - We report ab initio atomistic simulations of hydrous silicate melts under deep upper mantle to shallow lower mantle conditions and use them to parameterise density and viscosity across the ternary system MgO-SiO2-H2O (MSH). On the basis of phase relations in the MSH system, primary hydrous partial melts of the mantle have 40-50 mol% H2O. Our results show that these melts will be positively buoyant at the upper and lower boundaries of the mantle transition zone except in very iron-rich compositions, where ≳ 75% Mg is substituted by Fe. Hydrous partial melts will also be highly inviscid. Our results indicate that if melting occurs when wadsleyite transforms to olivine at 410 km, melts will be buoyant and ponding of melts is unexpected. Box models of mantle circulation incorporating the upward mobility of partial melts above and below the transition zone suggest that the upper mantle becomes efficiently hydrated at the expense of the transition zone such that large differences in H2O concentration between the upper mantle, transition zone and lower mantle are difficult to maintain on timescales of mantle recycling. The MORB source mantle with ∼0.02-0.04 wt% H2O may be indicative of the H2O content of the transition zone and lower mantle, resulting in a bulk mantle H2O content of the order 0.5 to 1 ocean mass, which is consistent with geochemical constraints and estimates of subduction ingassing.

AB - We report ab initio atomistic simulations of hydrous silicate melts under deep upper mantle to shallow lower mantle conditions and use them to parameterise density and viscosity across the ternary system MgO-SiO2-H2O (MSH). On the basis of phase relations in the MSH system, primary hydrous partial melts of the mantle have 40-50 mol% H2O. Our results show that these melts will be positively buoyant at the upper and lower boundaries of the mantle transition zone except in very iron-rich compositions, where ≳ 75% Mg is substituted by Fe. Hydrous partial melts will also be highly inviscid. Our results indicate that if melting occurs when wadsleyite transforms to olivine at 410 km, melts will be buoyant and ponding of melts is unexpected. Box models of mantle circulation incorporating the upward mobility of partial melts above and below the transition zone suggest that the upper mantle becomes efficiently hydrated at the expense of the transition zone such that large differences in H2O concentration between the upper mantle, transition zone and lower mantle are difficult to maintain on timescales of mantle recycling. The MORB source mantle with ∼0.02-0.04 wt% H2O may be indicative of the H2O content of the transition zone and lower mantle, resulting in a bulk mantle H2O content of the order 0.5 to 1 ocean mass, which is consistent with geochemical constraints and estimates of subduction ingassing.

KW - hydrous melts

KW - density

KW - viscosity

KW - transition zone

KW - molecular dynamics

KW - mantle H2O cycle

U2 - 10.1016/j.epsl.2022.117408

DO - 10.1016/j.epsl.2022.117408

M3 - Article (Academic Journal)

SN - 0012-821X

VL - 581

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

M1 - 117408

ER -

Hydrous silicate melts and the deep mantle H2O cycle

Abstract

Bibliographical note

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Ab initio Molecular Dynamics Trajectories for Hydrous Silicate Melts

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