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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

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!



Seismological studies of iceland
Seismological studies of Iceland Iceland plume is like.

Foulger et al. (2003)


Crustal structure
Crustal structure Iceland plume is like.

  • 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 Iceland plume is like.structure

The melting anomaly has always been centred on the

mid-Atlantic ridge


Iceland mantle tomography
Iceland: Mantle tomography Iceland plume is like.

  • 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? Iceland plume is like.

Whole-mantle tomography

Bijwaard & Spakman (1999)


Transition zone discontinuities
Transition zone discontinuities Iceland plume is like.

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

Du et al. (2006)


Transition zone discontinuities1
Transition zone discontinuities Iceland plume is like.

  • 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 Iceland plume is like.

Can be investigated using:

  • Petrology

  • Seismology

  • Modeling bathymetry

  • Modeling vertical motion

  • Heat flow


Petrological temperature
Petrological temperature Iceland plume is like.

~ 100 K temperature anomaly for Iceland relative to MORB

Arndt (2005)


Petrological temperature1

? Iceland plume is like.

Iceland?

Petrological temperature

Hawaii 1570˚

MORs 1280-1400˚

Gudfinnsson et al. (2003)


Temperature seismology
Temperature: Seismology Iceland plume is like.

Vs

Vertical scale

x 10

DT ~ 200˚C

DT ~ 100˚C

Ritsema & Montagner (2003)

Vertical scale x 1

Iceland


Temperature iceland
Temperature: Iceland Iceland plume is like.

Foulger et al. (2005)


Uplift magnitude duration
Uplift: Magnitude & Duration Iceland plume is like.

  • 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 Iceland plume is like.

FAROES &

E GREENLAND

ODP

158

BRITISH

PROVINCE

1. History of magmatism

Jones (2005)

61-59 Ma

54 Ma


Summary
Summary Iceland plume is like.

  • 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 Iceland plume is like.

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”) Iceland plume is like.

Many others intraplate extensional areas

PLATE: Lithospheric extension


Plate variable mantle fertility
PLATE: Variable mantle fertility Iceland plume is like.

  • Possible sources:

    • recycling of subducted slabs in upper mantle

Peacock (2000)


Plate variable mantle fertility1
PLATE: Variable mantle fertility Iceland plume is like.

  • Possible sources:

    • delamination of continental lithosphere

Schott et al. (2000)


The liquidus solidus of subducted crust are lower than peridotite

Pyrolite Iceland plume is like.

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 Iceland plume is like.

  • 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 plume is like.


Iceland extension
Iceland: Extension Iceland plume is like.

Jones (2005)

Iceland has been persistently centred on the mid-Atlantic ridge


Iceland mantle fertility

Relationship to the Caledonian suture Iceland plume is like.

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 Iceland plume is like.

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 Iceland plume is like.

  • 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 Iceland plume is like.

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 plume is like.

  • 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) Iceland plume is like.

Tectonics & crustal structure

Iceland is also a region of local, persistent tectonic instability


Iceland tectonic evolution
Iceland: Tectonic evolution Iceland plume is like.

Foulger (in press)


Iceland tectonic evolution1
Iceland: Tectonic evolution Iceland plume is like.

Foulger (2002)


Crustal structure2
Crustal structure Iceland plume is like.

The thickspot beneath Iceland may be a submerged oceanic microplate


Iceland the mantle anomaly
Iceland: The mantle anomaly Iceland plume is like.

  • 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 Iceland plume is like.

  • Superficially, several observations are consistent with plume theory

  • Closer examination virtually never fulfills the predictions of plume theory


Summary2
Summary Iceland plume is like.

  • 2 approaches:

    • adapt plume theory to fit

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


Resources
Resources: Iceland plume is like.

http://www.mantleplumes.org/


That s all folks

That’s all folks Iceland plume is like.


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