mantle plumes, plumes and ‘plumes’: d o we need all of them?

MANTLE PLUMES, plumes and ‘plumes’: do we need all of them?

1. History of plumes and definitions2. Plumes are thought to be required by evidence: a. Temperature b. Age progressive volcanism c. Heat flow d. Trace elements e. Radiogenic isotopes f. Seismic tomography g. Uplift shape and history h. Volume of magma3. Does the evidence require plumes?4. New models for melting anomalies: case studies a. Permo-Triassic Siberian Traps b. Late Cenozoic volcanism of Central Asia5. Conclusions

Alexei V. Ivanov Institute of the Earth’s Crust SB RAS, Irkutsk Russia

www.mantleplumes.org

Alexei Ivanov: a lecture at the Paleomagnetism and geochronology laboratory in Beijing (PGLB), China, January 11, 2006. The lecture was given on the occasion of his visit sponsored by a PGLB visitor grant.

Special thanks to Prof. R. Zhu and Dr. H. He.

0

10

20

30

40

50

60

70

1970 1975 1980 1985 1990 1995 2000 2005Year

Number of publications

"Plume" in titles (GeoRef database)

Critiques of the plume model

Syrope experiments and high 3He/4He in oceanic basalts

P-cubed GSA special paper 388

Modified after (Anderson and Natland, 2005; Ivanov, 2006 in press)

Morgan, 1971

History of plumes and definitions

Why current skepticism?

Morgan’s evidence and assumptions


1. Oceanic island chains (e.g. Hawaii) do not associate with lithospheric plate boundaries and hence cannot be explained by plate tectonics;

2. Age progressive volcanism requires stable source of heat (hot spots) (after Wilson, 1963);

3. Upper mantle is vigorously convecting and hence the source of heat is somewhere below (source is most likely in the D’’ layer);

4. Oceanic island basalts are enriched in incompatible elements compared with depleted mid-oceanic ridge basalts, hence source is primitive in composition (Earth’s lower mantle);

5. Hot spots lie atop of localized thermal upwellings referred to as plumes;

6. Plumes represent the major part of upraising convective flow;7. Plumes give the force for plate tectonics.



In fluid mechanics literature, "plumes" refer to upwelling or downwelling

driven by self-buoyancy (Korenaga, 2005)

A mantle plume is a localised, roughly axisymmetric upwelling of buoyant

rock, originating from a boundary layer deep within the Earth (Saunders, 2004)

... surface hotspots on Earth may have three distinct origins: (a) <primary plumes> would originate from the deepest part of the lower mantle (... ‘Morganian’ <plumes>) (b) <Secondary> plumes originate from ...the top of the large transient domes that correspond to the superswells. (c) The remainder could be upper mantle features, and in that sense ‘Andersonian’ (Courtillot et al., 2003).


Plume, hotspot, wetspot, melting anomaly - a region of active or ancient volcanism not associated with MOR- and IA-types of volcanism.Superplume, superswell, megaplume, reheated slab - thermal and/or thermochemical broad upwelling structure either traversing through the whole mantle or located in the lower mantle on a scale of >108 yr.Lower mantle plume, primary plume, Morganian plume - thermal and/or thermochemical localized upwelling structure traversing through the whole mantle to the subsurface.Upper mantle plume, secondary plume - thermal and/or thermo-chemical localized upwelling structure originating in the transitional zone.Andersonian plume - asthenospheric structure, which is not a plume in any sense.


The classical Morganian plume probably does not exist

Arguments pro and contra

Plumes are thought to be required by evidenceTemperature

Does evidence require plumes?Temperature

Plumes are thought to be required by evidenceAge progressive volcanism

Age increase

Plumes are fixed - plates are moving No

Does evidence require plumes? Age progressive volcanism

Raymond et al., 2000

Fixed plumes gone with the <mantle?> wind


Stuart, 2005

Hawaiian chain is an effect of thermoelastic propagating crack?


Rasskazov et al., 1997; 2000

Example of complex stress conditionsin intracontinental setting

Dobretsov et al (2001) use as example of moving plume

Plumes are thought to be required by evidenceHeat flow Hofmeister and Criss, 2004

Total output is 44 TW >than radiogenic output of 20 TW,hence core must contribute heat to the surface

1. Measured heat flow value for oceanic crust is underestimated 2. Half space cooling model used instead of measurements -> 44 TW3. BSE is made of CI chondrite -> 20 TW

Does evidence require plumes?Heat flow Hofmeister and Criss, 2004

Total output 31 TW ~ radiogenic output 31 TW if BSE is made of EH

Is the half space cooling model is better than direct measurements ???

Plumes are thought to be required by evidenceTrace elements

0.1

1.0

10.0

100.0

Cs Rb Ba Th U K Nb Ta La Ce Pb Pr Sr P Zr Hf Sm Ti Y Yb

Rock/Mantle

OIBE-MORBMORBIAB (Mariana average)

MORB and IAB are from depleted upper mantle.OIB must come from somewhere else (lower mantle?)

0.1

1.0

10.0

100.0

Cs Rb Ba Th U K Nb Ta La Ce Pb Pr Sr P Zr Hf Sm Ti Y Yb

Rock/Mantle

OIBE-MORBMORBIAB (Mariana average)

Does evidence require plumes?Trace elements

Ontong-Java

There are many examples when studied basalts do not resemble OIB-trace element component, but they are still considered to be of lower mantle plume origin

Plumes are thought to be required by evidenceRadiogenic isotopes

Elam and Stuart, 2004

Icelandplume

Icelandplume

Does evidence require plumes?Radiogenic isotopes (Helium)

Class et al., 2005

Icelandplume

Icelandplume

Elam and Stuart, 2004

Does evidence require plumes?Radiogenic isotopes (Helium)

Anderson, 2000, 2001

Comoroplume

Icelandplume

Plumes are thought to be required by evidenceSeismic tomography

Tahiti/Cook

300

650

1000

1450

1900

2350

2800

HawaiiIceland

Montelli et al., 2004

Plumes are imaged via seismic tomography

Does evidence require plumes?Seismic tomography

Ritsema and Allen, 2002

Plume from the core/mantle boundary or lowermost mantle

RA2002 M2004Afar yes noBowie yes noHawaii yes noIceland yes noReunion no noTristan no noLouisville yes noSamoa yes noTahiti no yesAscension no yesAzores no yesCanary no yesEaster yes yesYellowstone no no

Plumes are thought to be required by evidenceUplift shape and history Campbell, 2005

Plumes support broad surface uplifts

Burov and Guillou-Frottier, 2005

Plumes are thought to be required by evidenceUplift shape and history

Does evidence require plumes?Uplift shape and history

Two most voluminous LIPs; Siberian Traps and Ontong-Java did not experienced uplift before the eruptions !

Korenaga, 2005

Plumes are thought to be required by evidenceLarge volume of magma

Large volume of magma requires high temperatureand hence lower mantle plumes

Does evidence require plumes?Large volume of magma

Actually, it does not

Siberian Traps example

New models for the melting anomalies: case studiesSiberian Traps

New models for the melting anomalies: case studiesSiberian Traps Ivanov et al., 2005


Modified after Ivanov and Balyshev, 2005


Ivanov et al., 2004; in preparation



Upper Mantle

Lower Mantle

Transitional zone


Data do not require lower mantle plume origin of the Siberian Traps

Data do require water in the mantle source of melting

Water is brought into the mantle by plate tectonic processes

New models for the melting anomalies: case studiesCentral Asia

Enriched isotopic signatures require long conservationof recycled material in the lower mantle and hence lower mantle plumes

Actually, it does not

Central Asian example



A number of papers refer Cenozoic volcanism of the Central Asia to be related with lower mantle plume on basis of geochemical data (e.g. Grachev, 2000; Yarmolyuk et al., 2003)

Zorin et al. (2004) revealed 7 upper mantle plumes on basis of gravity data

New models for the melting anomalies: case studiesCentral Asia Zorin et al., 2004

New models for the melting anomalies: case studiesCentral Asia Zorin et al., 2006 (2 papers in press)

Seismic tomography after model of Zhao, 2004

New models for the melting anomalies: case studiesCentral Asia Demonterova et al., 2005

New models for the melting anomalies: case studiesCentral Asia Demonterova et al., 2005

S=Do/Co I=[Rbo/Co][1-Po]

New models for the melting anomalies: case studiesCentral Asia Modified after Zorin et al., 2006 (in press)


Data do not require lower mantle plume origin of the Central Asian basalts

Data do require fertile fusible source and upper mantle plumes

(in terms of fluid dynamics)

Fertile source in the mantle is created byplate tectonic processes

Conclusions

1. The term ‘plume’ is poorly defined and hence should not be used in publications without special explanation of its meaning.

2. Evidence cited to prove plumes from the core and lower mantle in many instances do not require such interpretation.

3. Many alternative models can better explain melting anomalies than lower mantle plumes do.

Thanks!

mantle plumes, plumes and ‘plumes’: d o we need all of them?

Documents

mantle plumes

lower mantle plume

assumptionshistory of

definitionshistory of

upper mantle plume

morganian b plumes

primary plume

upper mantle features