Seismic and geochemical correlations at hotspots J.G. Konter, T.W. Becker

Seismic and geochemical Seismic and geochemical correlations at hotspotscorrelations at hotspots

J.G. Konter, T.W. BeckerJ.G. Konter, T.W. Becker

Konter and Becker, 2012Konter and Becker, 2012

OutlineOutline

Visual (map) correlations at hotspotsVisual (map) correlations at hotspots

Correlating actual numbers:Correlating actual numbers:•Hotspot locations and observationsHotspot locations and observations•Observations at hotspots: geophysical, Observations at hotspots: geophysical, geochemicalgeochemical•Bottom line: only some things correlate Bottom line: only some things correlate significantlysignificantly

Mantle Mantle ModelsModels

Geochemically:Geochemically:

Where to store Where to store

materials (noble materials (noble gas, EER, …)?gas, EER, …)?

Combine with Combine with geophysical geophysical

observations observations

Tackley, 2000Tackley, 2000

Geographical anomaliesGeographical anomalies““Dupal” hotspots located in the S hemisphere:Dupal” hotspots located in the S hemisphere:

Dupal = isotopically enriched by recycling (EM1, EM2)Dupal = isotopically enriched by recycling (EM1, EM2)

Hart, 1984Hart, 1984

Simplest correlationsSimplest correlations““Dupal” hotspots plot on top of seismically slow areasDupal” hotspots plot on top of seismically slow areas

=> Correlation significance?=> Correlation significance?

Castillo, 1988Castillo, 1988

Gradients ?Gradients ?

Locations seem to fit Locations seem to fit gradientsgradients

=> for same CMB => for same CMB area, gradients have area, gradients have ~2x more hotspots~2x more hotspots

Thorne et al., 2004Thorne et al., 2004

Adding LIPs - gradientsAdding LIPs - gradientsHotspot correlations done by several groupsHotspot correlations done by several groups

Gradients seem importantGradients seem important

Original eruptive locations LIPs “align” with hotspotsOriginal eruptive locations LIPs “align” with hotspotsTorsvik et al., 2006Torsvik et al., 2006

Mathematical correlationsMathematical correlationsVertical correlations hotspot-seismic less significant than Vertical correlations hotspot-seismic less significant than tilted conduitstilted conduits

Boschi et al, 2008Boschi et al, 2008

Including geochemistryIncluding geochemistry

Besides location, does Besides location, does geochemistry correlate?geochemistry correlate?

Raw ratios (PCA) or Raw ratios (PCA) or “end-members”“end-members”

Use: Sr-Nd-Pb isotope Use: Sr-Nd-Pb isotope data radiate out from data radiate out from FOZO/C to define FOZO/C to define “mantle tetrahedron”“mantle tetrahedron”

W. WhiteW. White

Isotope spaceIsotope spaceFor end-members, define measure For end-members, define measure of distance: of distance: distance from center distance from center (FOZO/C) to end-member(FOZO/C) to end-member

Konter et al., 2008Konter et al., 2008

Independent componentsIndependent components

Contrary to PCA, Contrary to PCA, underlying distribution underlying distribution can be non-gaussiancan be non-gaussian

Separates MORB from Separates MORB from OIBOIB

Iwamori and Albarède, 2008Iwamori and Albarède, 2008

Correlations Correlations - Only few significant- Only few significant Konter and Becker, 2012Konter and Becker, 2012

Significant:Significant:

depth –EM1,2,HIMUdepth –EM1,2,HIMU

EM1 –Vs-200EM1 –Vs-200

EM2 – Vs-CMBEM2 – Vs-CMB

C – Vs-200C – Vs-200

Potential temp. – CPotential temp. – C

NOTE: no correlation NOTE: no correlation for gradientsfor gradients

Significance of CorrelationsSignificance of Correlations

Monte Carlo: Monte Carlo: randomize locations randomize locations vs composition: vs composition:

EM1 and C/FOZO EM1 and C/FOZO best, plume depth best, plume depth close for allclose for all


Actual correlationsActual correlationsEM1 (anti)correlates well with EM1 (anti)correlates well with depth, Vs-200kmdepth, Vs-200km

Anti-correlation C/FOZO with Anti-correlation C/FOZO with Vs-200kmVs-200km


Atlantic EM1Atlantic EM1S. American/African continental lavas with overlapping S. American/African continental lavas with overlapping compositions; source in lithosphere?compositions; source in lithosphere?

Particularly S. America argued as source by multiple Particularly S. America argued as source by multiple groupsgroups

Hawkesworth et al., 1986Hawkesworth et al., 1986

Atlantic EM1Atlantic EM1Return flow in mantle delivers EM1; direct hotspot Return flow in mantle delivers EM1; direct hotspot track/APM does not fittrack/APM does not fit

(same authors put EM1 back in plume in 2010)(same authors put EM1 back in plume in 2010)

Class and Le Roex, 2006Class and Le Roex, 2006

EM1 originEM1 originEM1 combination of deep source with shallow EM1 combination of deep source with shallow influence: influence: mixing in lithosphere works, but mixing in lithosphere works, but requires >50%requires >50%


Explanation EM1Explanation EM1

Combination of conduit vs tomography, shallow Combination of conduit vs tomography, shallow pollution of deep sourcepollution of deep source


Explanation C/FOZOExplanation C/FOZO

Anti-correlation C/FOZO vs Vs-200km:Anti-correlation C/FOZO vs Vs-200km:

Compositions present in ~ all hotspots, shallow Compositions present in ~ all hotspots, shallow correlation is notcorrelation is not

Anti-correlation from larger degree melt Anti-correlation from larger degree melt (enriched trace elements suggested by isotopes)(enriched trace elements suggested by isotopes)

Main issue: He isotopes most characteristics, but Main issue: He isotopes most characteristics, but not availablenot available

So correlations?So correlations?

Some correlations with some of the geochemical Some correlations with some of the geochemical parameters, but many observables do not parameters, but many observables do not correlate at hotspotscorrelate at hotspots

Even so, what do the Even so, what do the

correlations mean?correlations mean?

Documents

Seismic and geochemical correlations at hotspots J.G. Konter, T.W. Becker