Radial viscous fingering of hot asthenosphere within the Icelandic plume beneath the North Atlantic Ocean

C. M. Schoonman, N. J. White, D. Pritchard

Research output: Contribution to journalArticle

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Abstract

The Icelandic mantle plume has had a significant influence on the geologic and oceanographic evolution of the North Atlantic Ocean during Cenozoic times. Full-waveform tomographic imaging of this region shows that the planform of this plume has a complex irregular shape with significant shear wave velocity anomalies lying beneath the lithospheric plates at a depth of 100–200 km. The distribution of these anomalies suggests that about five horizontal fingers extend radially beneath the fringing continental margins. The best-imaged fingers lie beneath the British Isles and beneath western Norway where significant departures from crustal isostatic equilibrium have been measured. Here, we propose that these radial fingers are generated by a phenomenon known as the Saffman-Taylor instability. Experimental and theoretical analyses show that fingering occurs when a less viscous fluid is injected into a more viscous fluid. In radial, miscible fingering, the wavelength and number of fingers are controlled by the mobility ratio (i.e. the ratio of viscosities), by the Péclet number (i.e. the ratio of advective and diffusive transport rates), and by the thickness of the horizontal layer into which fluid is injected. We combine shear wave velocity estimates with residual depth measurements around the Atlantic margins to estimate the planform distribution of temperature and viscosity within a horizontal asthenospheric layer beneath the lithospheric plate. Our estimates suggest thathe mobility ratio is at least 20–50, that the Péclet number is Ο(104), and that the asthenospheric channel is 100 ± 20 km thick. The existence and planform of fingering is consistent with experimental observations and with theoretical arguments. A useful rule of thumb is that the wavelength of fingering is 5 ± 1 times the thickness of the horizontal layer. Our proposal has been further tested by examining plumes of different vigor and planform (e.g. Hawaii, Cape Verde, Yellowstone). Our results support the notion that dynamic to pography of the Earth’s surface can be influenced by fast, irregular horizontal flow within thin, but rapidly evolving, asthenospheric fingers.
Original languageEnglish
Pages (from-to)51-61
Number of pages11
JournalEarth and Planetary Science Letters
Volume468
Early online date13 Apr 2017
DOIs
Publication statusPublished - 15 Jun 2017

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fingering
Planforms
asthenosphere
Atlantic Ocean
planforms
plumes
plume
Shear waves
Fluids
wave velocity
fluid
S-wave
viscous fluids
viscosity
S waves
Viscosity
wavelength
anomaly
Wavelength
estimates

Keywords

  • Iceland
  • Icelandic plume
  • mantle
  • North Atlantic Ocean
  • asthenosphere
  • Saffman-Taylor instability
  • Peclet number
  • Atlantic margins
  • planform distribution
  • mobility ratio

Cite this

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title = "Radial viscous fingering of hot asthenosphere within the Icelandic plume beneath the North Atlantic Ocean",
abstract = "The Icelandic mantle plume has had a significant influence on the geologic and oceanographic evolution of the North Atlantic Ocean during Cenozoic times. Full-waveform tomographic imaging of this region shows that the planform of this plume has a complex irregular shape with significant shear wave velocity anomalies lying beneath the lithospheric plates at a depth of 100–200 km. The distribution of these anomalies suggests that about five horizontal fingers extend radially beneath the fringing continental margins. The best-imaged fingers lie beneath the British Isles and beneath western Norway where significant departures from crustal isostatic equilibrium have been measured. Here, we propose that these radial fingers are generated by a phenomenon known as the Saffman-Taylor instability. Experimental and theoretical analyses show that fingering occurs when a less viscous fluid is injected into a more viscous fluid. In radial, miscible fingering, the wavelength and number of fingers are controlled by the mobility ratio (i.e. the ratio of viscosities), by the P{\'e}clet number (i.e. the ratio of advective and diffusive transport rates), and by the thickness of the horizontal layer into which fluid is injected. We combine shear wave velocity estimates with residual depth measurements around the Atlantic margins to estimate the planform distribution of temperature and viscosity within a horizontal asthenospheric layer beneath the lithospheric plate. Our estimates suggest thathe mobility ratio is at least 20–50, that the P{\'e}clet number is Ο(104), and that the asthenospheric channel is 100 ± 20 km thick. The existence and planform of fingering is consistent with experimental observations and with theoretical arguments. A useful rule of thumb is that the wavelength of fingering is 5 ± 1 times the thickness of the horizontal layer. Our proposal has been further tested by examining plumes of different vigor and planform (e.g. Hawaii, Cape Verde, Yellowstone). Our results support the notion that dynamic to pography of the Earth’s surface can be influenced by fast, irregular horizontal flow within thin, but rapidly evolving, asthenospheric fingers.",
keywords = "Iceland, Icelandic plume, mantle, North Atlantic Ocean, asthenosphere, Saffman-Taylor instability, Peclet number, Atlantic margins, planform distribution, mobility ratio",
author = "Schoonman, {C. M.} and White, {N. J.} and D. Pritchard",
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doi = "10.1016/j.epsl.2017.03.036",
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Radial viscous fingering of hot asthenosphere within the Icelandic plume beneath the North Atlantic Ocean. / Schoonman, C. M.; White, N. J.; Pritchard, D.

In: Earth and Planetary Science Letters, Vol. 468, 15.06.2017, p. 51-61.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Radial viscous fingering of hot asthenosphere within the Icelandic plume beneath the North Atlantic Ocean

AU - Schoonman, C. M.

AU - White, N. J.

AU - Pritchard, D.

PY - 2017/6/15

Y1 - 2017/6/15

N2 - The Icelandic mantle plume has had a significant influence on the geologic and oceanographic evolution of the North Atlantic Ocean during Cenozoic times. Full-waveform tomographic imaging of this region shows that the planform of this plume has a complex irregular shape with significant shear wave velocity anomalies lying beneath the lithospheric plates at a depth of 100–200 km. The distribution of these anomalies suggests that about five horizontal fingers extend radially beneath the fringing continental margins. The best-imaged fingers lie beneath the British Isles and beneath western Norway where significant departures from crustal isostatic equilibrium have been measured. Here, we propose that these radial fingers are generated by a phenomenon known as the Saffman-Taylor instability. Experimental and theoretical analyses show that fingering occurs when a less viscous fluid is injected into a more viscous fluid. In radial, miscible fingering, the wavelength and number of fingers are controlled by the mobility ratio (i.e. the ratio of viscosities), by the Péclet number (i.e. the ratio of advective and diffusive transport rates), and by the thickness of the horizontal layer into which fluid is injected. We combine shear wave velocity estimates with residual depth measurements around the Atlantic margins to estimate the planform distribution of temperature and viscosity within a horizontal asthenospheric layer beneath the lithospheric plate. Our estimates suggest thathe mobility ratio is at least 20–50, that the Péclet number is Ο(104), and that the asthenospheric channel is 100 ± 20 km thick. The existence and planform of fingering is consistent with experimental observations and with theoretical arguments. A useful rule of thumb is that the wavelength of fingering is 5 ± 1 times the thickness of the horizontal layer. Our proposal has been further tested by examining plumes of different vigor and planform (e.g. Hawaii, Cape Verde, Yellowstone). Our results support the notion that dynamic to pography of the Earth’s surface can be influenced by fast, irregular horizontal flow within thin, but rapidly evolving, asthenospheric fingers.

AB - The Icelandic mantle plume has had a significant influence on the geologic and oceanographic evolution of the North Atlantic Ocean during Cenozoic times. Full-waveform tomographic imaging of this region shows that the planform of this plume has a complex irregular shape with significant shear wave velocity anomalies lying beneath the lithospheric plates at a depth of 100–200 km. The distribution of these anomalies suggests that about five horizontal fingers extend radially beneath the fringing continental margins. The best-imaged fingers lie beneath the British Isles and beneath western Norway where significant departures from crustal isostatic equilibrium have been measured. Here, we propose that these radial fingers are generated by a phenomenon known as the Saffman-Taylor instability. Experimental and theoretical analyses show that fingering occurs when a less viscous fluid is injected into a more viscous fluid. In radial, miscible fingering, the wavelength and number of fingers are controlled by the mobility ratio (i.e. the ratio of viscosities), by the Péclet number (i.e. the ratio of advective and diffusive transport rates), and by the thickness of the horizontal layer into which fluid is injected. We combine shear wave velocity estimates with residual depth measurements around the Atlantic margins to estimate the planform distribution of temperature and viscosity within a horizontal asthenospheric layer beneath the lithospheric plate. Our estimates suggest thathe mobility ratio is at least 20–50, that the Péclet number is Ο(104), and that the asthenospheric channel is 100 ± 20 km thick. The existence and planform of fingering is consistent with experimental observations and with theoretical arguments. A useful rule of thumb is that the wavelength of fingering is 5 ± 1 times the thickness of the horizontal layer. Our proposal has been further tested by examining plumes of different vigor and planform (e.g. Hawaii, Cape Verde, Yellowstone). Our results support the notion that dynamic to pography of the Earth’s surface can be influenced by fast, irregular horizontal flow within thin, but rapidly evolving, asthenospheric fingers.

KW - Iceland

KW - Icelandic plume

KW - mantle

KW - North Atlantic Ocean

KW - asthenosphere

KW - Saffman-Taylor instability

KW - Peclet number

KW - Atlantic margins

KW - planform distribution

KW - mobility ratio

UR - http://www.sciencedirect.com/science/journal/0012821X

U2 - 10.1016/j.epsl.2017.03.036

DO - 10.1016/j.epsl.2017.03.036

M3 - Article

VL - 468

SP - 51

EP - 61

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

SN - 0012-821X

ER -