A small, unextractable melt fraction as the cause for the low velocity zone

Kate Selway, J. P. O'Donnell

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Throughout the oceanic asthenosphere there exists a zone of seismic velocities that are lower than would be predicted. The cause of this low velocity zone (LVZ), whether partial melt or solid-state mechanisms, has been debated for decades. We investigate the LVZ by considering seismic and magnetotelluric data from tectonically stable, ∼70 Myr old lithosphere in the central Pacific Ocean. We utilise recent experimental advances on the influence of partial melt and seismic attenuation. Results show that the LVZ is characterised by a small volume of interconnected melt and by low hydrogen contents. Beneath the LVZ, the asthenosphere does not contain partial melt but has high hydrogen contents and low attenuation values, indicating large grain sizes and/or low oxygen fugacities. To explain these observations, we propose that a small amount of unextractable melt is trapped in the asthenosphere after melting at mid-ocean ridges.

LanguageEnglish
Pages117-124
Number of pages8
JournalEarth and Planetary Science Letters
Volume517
DOIs
Publication statusPublished - 1 Jul 2019

Fingerprint

low velocity zone
low speed
asthenosphere
melt
causes
attenuation
Hydrogen
mid-ocean ridges
Magnetotellurics
Pacific Ocean
hydrogen
seismic attenuation
lithosphere
mid-ocean ridge
fugacity
seismic velocity
grain size
melting
solid state
Melting

Keywords

  • asthenosphere
  • mantle
  • melt
  • low velocity zone
  • magnetotellurics
  • seismic

Cite this

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abstract = "Throughout the oceanic asthenosphere there exists a zone of seismic velocities that are lower than would be predicted. The cause of this low velocity zone (LVZ), whether partial melt or solid-state mechanisms, has been debated for decades. We investigate the LVZ by considering seismic and magnetotelluric data from tectonically stable, ∼70 Myr old lithosphere in the central Pacific Ocean. We utilise recent experimental advances on the influence of partial melt and seismic attenuation. Results show that the LVZ is characterised by a small volume of interconnected melt and by low hydrogen contents. Beneath the LVZ, the asthenosphere does not contain partial melt but has high hydrogen contents and low attenuation values, indicating large grain sizes and/or low oxygen fugacities. To explain these observations, we propose that a small amount of unextractable melt is trapped in the asthenosphere after melting at mid-ocean ridges.",
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A small, unextractable melt fraction as the cause for the low velocity zone. / Selway, Kate; O'Donnell, J. P.

In: Earth and Planetary Science Letters, Vol. 517, 01.07.2019, p. 117-124.

Research output: Contribution to journalArticleResearchpeer-review

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T1 - A small, unextractable melt fraction as the cause for the low velocity zone

AU - Selway, Kate

AU - O'Donnell, J. P.

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N2 - Throughout the oceanic asthenosphere there exists a zone of seismic velocities that are lower than would be predicted. The cause of this low velocity zone (LVZ), whether partial melt or solid-state mechanisms, has been debated for decades. We investigate the LVZ by considering seismic and magnetotelluric data from tectonically stable, ∼70 Myr old lithosphere in the central Pacific Ocean. We utilise recent experimental advances on the influence of partial melt and seismic attenuation. Results show that the LVZ is characterised by a small volume of interconnected melt and by low hydrogen contents. Beneath the LVZ, the asthenosphere does not contain partial melt but has high hydrogen contents and low attenuation values, indicating large grain sizes and/or low oxygen fugacities. To explain these observations, we propose that a small amount of unextractable melt is trapped in the asthenosphere after melting at mid-ocean ridges.

AB - Throughout the oceanic asthenosphere there exists a zone of seismic velocities that are lower than would be predicted. The cause of this low velocity zone (LVZ), whether partial melt or solid-state mechanisms, has been debated for decades. We investigate the LVZ by considering seismic and magnetotelluric data from tectonically stable, ∼70 Myr old lithosphere in the central Pacific Ocean. We utilise recent experimental advances on the influence of partial melt and seismic attenuation. Results show that the LVZ is characterised by a small volume of interconnected melt and by low hydrogen contents. Beneath the LVZ, the asthenosphere does not contain partial melt but has high hydrogen contents and low attenuation values, indicating large grain sizes and/or low oxygen fugacities. To explain these observations, we propose that a small amount of unextractable melt is trapped in the asthenosphere after melting at mid-ocean ridges.

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