Extreme redox variations in a superdeep diamond from a subducted slab

Fabrizio Nestola; Margo E. Regier; Robert W. Luth; D. Graham Pearson; Thomas Stachel; Catherine McCammon; Michelle D. Wenz; Steven D. Jacobsen; Chiara Anzolini; Luca Bindi; Jeffrey W. Harris

doi:10.1038/s41586-022-05392-8

Extreme redox variations in a superdeep diamond from a subducted slab

Fabrizio Nestola^*, Margo E. Regier, Robert W. Luth, D. Graham Pearson, Thomas Stachel, Catherine McCammon, Michelle D. Wenz, Steven D. Jacobsen, Chiara Anzolini, Luca Bindi, Jeffrey W. Harris

^*Corresponding author for this work

Earth and Planetary Sciences

Research output: Contribution to journal › Article › peer-review

10 Scopus citations

Abstract

The introduction of volatile-rich subducting slabs to the mantle may locally generate large redox gradients, affecting phase stability, element partitioning and volatile speciation¹. Here we investigate the redox conditions of the deep mantle recorded in inclusions in a diamond from Kankan, Guinea. Enstatite (former bridgmanite), ferropericlase and a uniquely Mg-rich olivine (Mg# 99.9) inclusion indicate formation in highly variable redox conditions near the 660 km seismic discontinuity. We propose a model involving dehydration, rehydration and dehydration in the underside of a warming slab at the transition zone–lower mantle boundary. Fluid liberated by dehydration in a crumpled slab, driven by heating from the lower mantle, ascends into the cooler interior of the slab, where the H₂O is sequestered in new hydrous minerals. Consequent fractionation of the remaining fluid produces extremely reducing conditions, forming Mg-end-member ringwoodite. This fractionating fluid also precipitates the host diamond. With continued heating, ringwoodite in the slab surrounding the diamond forms bridgmanite and ferropericlase, which is trapped as the diamond grows in hydrous fluids produced by dehydration of the warming slab.

Original language	English (US)
Pages (from-to)	85-89
Number of pages	5
Journal	Nature
Volume	613
Issue number	7942
DOIs	https://doi.org/10.1038/s41586-022-05392-8
State	Published - Jan 5 2023

Funding

This research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We acknowledge the support of GeoSoilEnviroCARS (Sector 13), which is supported by the US National Science Foundation (NSF) – Earth Sciences (EAR-1128799), and the Department of Energy, Geosciences (DE-FG02-94ER14466), and staff scientists M. Newville, T. Lanzirotti and M. Rivers. S.D.J. acknowledges support from NSF grant no. EAR-1853521. NSERC Discovery grants to R.W.L., D.G.P. and T.S. funded aspects of this research. The authors acknowledge A. Rohrbach and K. Kiseeva for very valuable comments that prompted a re-think of our f estimate and formation model. O2

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@article{60477457d9184793b19cff43805e8afb,

title = "Extreme redox variations in a superdeep diamond from a subducted slab",

abstract = "The introduction of volatile-rich subducting slabs to the mantle may locally generate large redox gradients, affecting phase stability, element partitioning and volatile speciation1. Here we investigate the redox conditions of the deep mantle recorded in inclusions in a diamond from Kankan, Guinea. Enstatite (former bridgmanite), ferropericlase and a uniquely Mg-rich olivine (Mg# 99.9) inclusion indicate formation in highly variable redox conditions near the 660 km seismic discontinuity. We propose a model involving dehydration, rehydration and dehydration in the underside of a warming slab at the transition zone–lower mantle boundary. Fluid liberated by dehydration in a crumpled slab, driven by heating from the lower mantle, ascends into the cooler interior of the slab, where the H2O is sequestered in new hydrous minerals. Consequent fractionation of the remaining fluid produces extremely reducing conditions, forming Mg-end-member ringwoodite. This fractionating fluid also precipitates the host diamond. With continued heating, ringwoodite in the slab surrounding the diamond forms bridgmanite and ferropericlase, which is trapped as the diamond grows in hydrous fluids produced by dehydration of the warming slab.",

author = "Fabrizio Nestola and Regier, {Margo E.} and Luth, {Robert W.} and Pearson, {D. Graham} and Thomas Stachel and Catherine McCammon and Wenz, {Michelle D.} and Jacobsen, {Steven D.} and Chiara Anzolini and Luca Bindi and Harris, {Jeffrey W.}",

note = "Funding Information: This research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We acknowledge the support of GeoSoilEnviroCARS (Sector 13), which is supported by the US National Science Foundation (NSF) – Earth Sciences (EAR-1128799), and the Department of Energy, Geosciences (DE-FG02-94ER14466), and staff scientists M. Newville, T. Lanzirotti and M. Rivers. S.D.J. acknowledges support from NSF grant no. EAR-1853521. NSERC Discovery grants to R.W.L., D.G.P. and T.S. funded aspects of this research. The authors acknowledge A. Rohrbach and K. Kiseeva for very valuable comments that prompted a re-think of our f estimate and formation model. O2 Publisher Copyright: {\textcopyright} 2023, The Author(s), under exclusive licence to Springer Nature Limited.",

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doi = "10.1038/s41586-022-05392-8",

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AU - Nestola, Fabrizio

AU - Regier, Margo E.

AU - Luth, Robert W.

AU - Pearson, D. Graham

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AU - McCammon, Catherine

AU - Wenz, Michelle D.

AU - Jacobsen, Steven D.

AU - Anzolini, Chiara

AU - Bindi, Luca

AU - Harris, Jeffrey W.

N1 - Funding Information: This research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We acknowledge the support of GeoSoilEnviroCARS (Sector 13), which is supported by the US National Science Foundation (NSF) – Earth Sciences (EAR-1128799), and the Department of Energy, Geosciences (DE-FG02-94ER14466), and staff scientists M. Newville, T. Lanzirotti and M. Rivers. S.D.J. acknowledges support from NSF grant no. EAR-1853521. NSERC Discovery grants to R.W.L., D.G.P. and T.S. funded aspects of this research. The authors acknowledge A. Rohrbach and K. Kiseeva for very valuable comments that prompted a re-think of our f estimate and formation model. O2 Publisher Copyright: © 2023, The Author(s), under exclusive licence to Springer Nature Limited.

PY - 2023/1/5

Y1 - 2023/1/5

N2 - The introduction of volatile-rich subducting slabs to the mantle may locally generate large redox gradients, affecting phase stability, element partitioning and volatile speciation1. Here we investigate the redox conditions of the deep mantle recorded in inclusions in a diamond from Kankan, Guinea. Enstatite (former bridgmanite), ferropericlase and a uniquely Mg-rich olivine (Mg# 99.9) inclusion indicate formation in highly variable redox conditions near the 660 km seismic discontinuity. We propose a model involving dehydration, rehydration and dehydration in the underside of a warming slab at the transition zone–lower mantle boundary. Fluid liberated by dehydration in a crumpled slab, driven by heating from the lower mantle, ascends into the cooler interior of the slab, where the H2O is sequestered in new hydrous minerals. Consequent fractionation of the remaining fluid produces extremely reducing conditions, forming Mg-end-member ringwoodite. This fractionating fluid also precipitates the host diamond. With continued heating, ringwoodite in the slab surrounding the diamond forms bridgmanite and ferropericlase, which is trapped as the diamond grows in hydrous fluids produced by dehydration of the warming slab.

AB - The introduction of volatile-rich subducting slabs to the mantle may locally generate large redox gradients, affecting phase stability, element partitioning and volatile speciation1. Here we investigate the redox conditions of the deep mantle recorded in inclusions in a diamond from Kankan, Guinea. Enstatite (former bridgmanite), ferropericlase and a uniquely Mg-rich olivine (Mg# 99.9) inclusion indicate formation in highly variable redox conditions near the 660 km seismic discontinuity. We propose a model involving dehydration, rehydration and dehydration in the underside of a warming slab at the transition zone–lower mantle boundary. Fluid liberated by dehydration in a crumpled slab, driven by heating from the lower mantle, ascends into the cooler interior of the slab, where the H2O is sequestered in new hydrous minerals. Consequent fractionation of the remaining fluid produces extremely reducing conditions, forming Mg-end-member ringwoodite. This fractionating fluid also precipitates the host diamond. With continued heating, ringwoodite in the slab surrounding the diamond forms bridgmanite and ferropericlase, which is trapped as the diamond grows in hydrous fluids produced by dehydration of the warming slab.

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Extreme redox variations in a superdeep diamond from a subducted slab

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