mantle plumes, plumes and ‘plumes’: d o we need all of them?
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MANTLE PLUMES, plumes and ‘plumes’: d o we need all of them?. Alexei V. Ivanov Institute of the Earth’s Crust SB RAS, Irkutsk Russia www.mantleplumes.org. 1. History of plumes and definitions 2. Plumes are thought to be required by evidence: a. Temperature b. Age progressive volcanism - PowerPoint PPT PresentationTRANSCRIPT
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.
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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
History of plumes and definitions
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.
History of plumes and definitions
History of plumes and definitions
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).
History of plumes and definitions
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.
History of plumes and definitions
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
Does evidence require plumes? Age progressive volcanism
Stuart, 2005
Hawaiian chain is an effect of thermoelastic propagating crack?
Does evidence require plumes? Age progressive volcanism
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
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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?)
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Cs Rb Ba Th U K Nb Ta La Ce Pb Pr Sr P Zr Hf Sm Ti Y Yb
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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
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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
New models for the melting anomalies: case studiesSiberian Traps
New models for the melting anomalies: case studiesSiberian Traps
Modified after Ivanov and Balyshev, 2005
New models for the melting anomalies: case studiesSiberian Traps
Ivanov et al., 2004; in preparation
New models for the melting anomalies: case studiesSiberian Traps
Ivanov et al., 2004; in preparation
New models for the melting anomalies: case studiesSiberian Traps
Ivanov et al., 2004; in preparation
New models for the melting anomalies: case studiesSiberian Traps
Ivanov et al., 2004; in preparation
Upper Mantle
Lower Mantle
Transitional zone
New models for the melting anomalies: case studiesSiberian Traps
Ivanov et al., 2004; in preparation
New models for the melting anomalies: case studiesSiberian Traps
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
New models for the melting anomalies: case studiesCentral Asia
New models for the melting anomalies: case studiesCentral Asia
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
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)
New models for the melting anomalies: case studiesCentral Asia
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!