No plume beneath iceland
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No Plume Beneath Iceland. talk given at the Colorado School of Mines, 2nd March 2006 Gillian R. Foulger Durham University, U.K. Evidence in support of a plume beneath Iceland. History of magmatism Uplift High temperatures Crustal structure Mantle structure. DISKO. FAROES & E GREENLAND.

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No Plume Beneath Iceland

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No plume beneath iceland

No Plume Beneath Iceland

talk given at the Colorado School of Mines, 2nd March 2006

Gillian R. Foulger

Durham University, U.K.


Evidence in support of a plume beneath iceland

Evidence in support of a plume beneath Iceland

  • History of magmatism

  • Uplift

  • High temperatures

  • Crustal structure

  • Mantle structure


1 history of magmatism

DISKO

FAROES &

E GREENLAND

ODP

158

BRITISH

PROVINCE

1. History of magmatism

Jones (2005)

61-59 Ma

54 Ma


1 history of magmatism iceland

Formed over the last 54 Million years

Thick crust

1. History ofmagmatism:Iceland


2 uplift

2. Uplift

400-900 m

420-620 m

380-590 m

180-425 m

0-100 m

500-800 m

0 - 200 m

0-200 m

Jones (2005)


2 uplift1

2. Uplift

  • Uplift rapid

  • Approached 1 km in some places

400-900 m

420-620 m

380-590 m

180-425 m

0-100 m

500-800 m

0 - 200 m

0-200 m

Jones (2005)


3 high temperatures

3. High-temperatures

~ 100 K temperature anomaly for Iceland relative to MORB

Arndt (2005)


4 crustal structure

4. Crustal structure

Foulger et al. (2003)

Crustal structure from receiver functions


5 mantle structure

5. Mantle structure

Whole-mantle tomography: A plume from the core-mantle boundary.

Bijwaard & Spakman (1999)


The iceland plume

The Iceland plume?

A slam dunk!


Let us look in detail to find out more about what the iceland plume is like

Let us look in detail, to find out more about what the Iceland plume is like.


Seismological studies of iceland

Seismological studies of Iceland

Foulger et al. (2003)


Crustal structure

Crustal structure

  • Variations in crustal thickness should be parallel to spreading direction

  • Crust should be thickest in the west, behind the plume

Foulger et al. (2003)


Crustal structure1

Crustal structure

The melting anomaly has always been centred on the

mid-Atlantic ridge


Iceland mantle tomography

Iceland: Mantle tomography

  • Over 2,000,000 data

    • S-wave arrival times (S, SS, SSS, ScS & SKS)

    • fundamental- & higher-mode Rayleigh-wave phase velocities

    • normal-mode frequencies

  • Probably best spherical harmonic model for the transition zone & mid-mantle

Ritsema et al. (1999)


Whole mantle tomography

Hudson Bay plume?

Whole-mantle tomography

Bijwaard & Spakman (1999)


Transition zone discontinuities

Transition zone discontinuities

Predicted topography on the 410-km and 650-km discontinuities

Du et al. (2006)


Transition zone discontinuities1

Transition zone discontinuities

  • 410 warps down by 15 km

  • 650 flat

  • No evidence for anomalous structure or physical conditions at 650 km beneath Iceland

Du et al. (2006)


Temperature

Temperature

Can be investigated using:

  • Petrology

  • Seismology

  • Modeling bathymetry

  • Modeling vertical motion

  • Heat flow


Petrological temperature

Petrological temperature

~ 100 K temperature anomaly for Iceland relative to MORB

Arndt (2005)


Petrological temperature1

?

Iceland?

Petrological temperature

Hawaii 1570˚

MORs 1280-1400˚

Gudfinnsson et al. (2003)


Temperature seismology

Temperature: Seismology

Vs

Vertical scale

x 10

DT ~ 200˚C

DT ~ 100˚C

Ritsema & Montagner (2003)

Vertical scale x 1

Iceland


Temperature iceland

Temperature: Iceland

Foulger et al. (2005)


Uplift magnitude duration

Uplift: Magnitude & Duration

  • 61 Ma uplift associated with British igneous activity variable, low amplitude (few 100 m) & localised.

  • 54 Ma uplift associated with igneous activity distant from proposed plume, high amplitude (up to 1 km) & widespread.

  • Time between onset and peak uplift for both igneous phases probably << 1 Myr.

  • Uplift history complex & not satisfactorily explained by any single published model.


1 history of magmatism1

DISKO

FAROES &

E GREENLAND

ODP

158

BRITISH

PROVINCE

1. History of magmatism

Jones (2005)

61-59 Ma

54 Ma


Summary

Summary

  • Variations in crustal thickness inconsistent with plume predictions

  • Mantle anomaly confined to upper mantle

  • No reliable evidence for plume-like temperatures

  • Uplift history complex and not well explained

  • Distribution of magmatism inconsistent with plume predictions


An alternative model

An alternative model

Plate tectonic processes (“PLATE”)

  • Two elements:

    • Variable source fertility

    • Extensional stress

      A cool, shallow, top-driven model


Plate lithospheric extension

Mid-ocean ridges (1/3 of all “hot spots”)

Many others intraplate extensional areas

PLATE: Lithospheric extension


Plate variable mantle fertility

PLATE: Variable mantle fertility

  • Possible sources:

    • recycling of subducted slabs in upper mantle

Peacock (2000)


Plate variable mantle fertility1

PLATE: Variable mantle fertility

  • Possible sources:

    • delamination of continental lithosphere

Schott et al. (2000)


The liquidus solidus of subducted crust are lower than peridotite

Pyrolite

Eclogite

The liquidus & solidus of subducted crust are lower than peridotite

  • Subducted crust transforms to eclogite at depth

  • Eclogite is extensively molten at the peridotite solidus

Cordery et al. (1997)


Geochemistry of hot spot lavas

Geochemistry of “hot spot” lavas

  • Can be modeled as fractional melting of MORB

  • Ocean Island Basalt (OIB) comes from recycled near-surface materials e.g., subducted oceanic crust

Hofmann & White (1982)


Iceland

Iceland


Iceland extension

Iceland: Extension

Jones (2005)

Iceland has been persistently centred on the mid-Atlantic ridge


Iceland mantle fertility

Relationship to the Caledonian suture

Recycled Iapetus crust in source?

Can remelting of Iapetus slabs account for the excess melt, geochemistry & petrology?

Iceland: Mantle fertility

Closure of Iapetus


Melt fraction temperature

Melt fraction : Temperature

Yaxley (2000)

A 30/70 eclogite-peridotite mixture can generate several times as much melt as peridotite


Geochemical evidence for crustal recycling

Geochemical evidence for crustal recycling

  • Recent papers: Korenaga & Keleman (2000); Breddam (2002); Chauvel & Hemond (2000)

  • Estimated primary mantle melt from Iceland, E & SE Greenland shows source mantle enriched in Fe; Mg# is as low as 0.87

  • Heterogeneity suggests MORB mantle also involved

  • Sr-Nd-Hf-Pb isotopes & dO18 suggest recycling of subducted, aged oceanic crust, ± sub-arc magmatism, ± sediments


Iceland ree patterns

Iceland: REE patterns

Foulger et al. (2005)

Iceland REE can be modeled by extensive melting of subducted crust + small amount of alkali olivine basalt


The alternative hypothesis is

The alternative hypothesis is...

  • Iceland is a “normal” part of the MAR where excess melt is produced from remelting Iapetus slabs

  • However, the amount of melt produced by isentropic upwelling of eclogite cannot at present be calculated


Tectonics crustal structure

Foulger et al. (2003)

Tectonics & crustal structure

Iceland is also a region of local, persistent tectonic instability


Iceland tectonic evolution

Iceland: Tectonic evolution

Foulger (in press)


Iceland tectonic evolution1

Iceland: Tectonic evolution

Foulger (2002)


Crustal structure2

Crustal structure

The thickspot beneath Iceland may be a submerged oceanic microplate


Iceland the mantle anomaly

Iceland: The mantle anomaly

  • Can be explained by 0.1% partial melt

    • a more fusible mantle composition

    • CO2 fluxing

  • Could simply be a place where the low-velocity zone is thicker

Iceland


Summary1

Summary

  • Superficially, several observations are consistent with plume theory

  • Closer examination virtually never fulfills the predictions of plume theory


Summary2

Summary

  • 2 approaches:

    • adapt plume theory to fit

    • accept that plume theory fails and boldly go where no man has gone before


Resources

Resources:

http://www.mantleplumes.org/


That s all folks

That’s all folks


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