Transcript Заголовок слайда отсутствует

MANTLE PLUMES, plumes and ‘plumes’: do 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
c. Heat flow
d. Trace elements
e. Radiogenic isotopes
f. Seismic tomography
g. Uplift shape and history
h. Volume of magma
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.
3. Does the evidence require plumes?
4. New models for melting anomalies: case studies
a. Permo-Triassic Siberian Traps
b. Late Cenozoic volcanism of Central Asia
5. Conclusions
History of plumes and definitions
Modified after (Anderson and Natland, 2005; Ivanov, 2006 in press)
70
"Plume" in titles (GeoRef database)
Number of publications
60
Syrope experiments and high
3
He/4He in oceanic basalts
50
40
P-cubed
GSA special
paper 388
30
20
Morgan, 1971
Critiques of the plume model
10
0
1970
1975
1980
1985
1990
1995
Year
Why current skepticism?
2000
2005
History of plumes and definitions
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
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 thermochemical 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 evidence
Temperature
Does evidence require plumes?
Temperature
Plumes are thought to be required by evidence
Age progressive volcanism
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
Dobretsov et al (2001) use as example of
moving plume
Example of complex stress conditions
in intracontinental setting
Plumes are thought to be required by evidence
Heat 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 TW
3. BSE is made of CI chondrite -> 20 TW
Does evidence require plumes?
Heat flow Hofmeister and Criss, 2004
Is the half space cooling model is better than direct measurements ???
Total output 31 TW ~ radiogenic output 31 TW if BSE is made of EH
Plumes are thought to be required by evidence
Trace elements
Rock/Mantle
100.0
10.0
1.0
OIB
E-MORB
MORB
IAB (Mariana average)
0.1
Cs
Rb
Ba Th
U
K
Nb
Ta
La
Ce Pb
Pr
Sr
P
Zr
Hf
Sm
Ti
Y
MORB and IAB are from depleted upper mantle.
OIB must come from somewhere else (lower mantle?)
Yb
Does evidence require plumes?
Trace elements
Rock/Mantle
100.0
10.0
Ontong-Java
1.0
OIB
E-MORB
MORB
IAB (Mariana average)
0.1
Cs
Rb
Ba Th
U
K
Nb
Ta
La
Ce Pb
Pr
Sr
P
Zr
Hf
Sm
Ti
Y
Yb
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 evidence
Radiogenic isotopes
Iceland
plume
Elam and Stuart, 2004
Iceland
plume
Does evidence require plumes?
Radiogenic isotopes (Helium)
Iceland
plume
Elam and Stuart, 2004
Class et al., 2005
Iceland
plume
Does evidence require plumes?
Radiogenic isotopes (Helium)
Comoro
plume
Iceland
plume
Anderson, 2000, 2001
Plumes are thought to be required by evidence
Seismic tomography
Montelli et al., 2004
Iceland
Hawaii
Tahiti/Cook
300
650
1000
1450
1900
2350
2800
Plumes are imaged via seismic tomography
Does evidence require plumes?
Seismic tomography
Plume from the core/mantle
boundary or lowermost mantle
Ritsema and Allen, 2002
RA2002
Afar
yes
Bowie
yes
Hawaii
yes
Iceland
yes
Reunion
no
Tristan
no
Louisville yes
Samoa
yes
Tahiti
no
Ascension no
Azores
no
Canary
no
Easter
yes
Yellowstone no
M2004
no
no
no
no
no
no
no
no
yes
yes
yes
yes
yes
no
Plumes are thought to be required by evidence
Uplift shape and history
Campbell, 2005
Plumes support broad surface uplifts
Plumes are thought to be required by evidence
Uplift shape and history
Burov and Guillou-Frottier, 2005
Does evidence require plumes?
Uplift shape and history
Korenaga, 2005
Two most voluminous
LIPs; Siberian Traps
and Ontong-Java did
not experienced uplift
before the eruptions !
Plumes are thought to be required by evidence
Large volume of magma
Large volume of magma requires high temperature
and 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 studies
Siberian Traps
New models for the melting anomalies: case studies
Siberian Traps
Ivanov et al., 2005
New models for the melting anomalies: case studies
Siberian Traps
New models for the melting anomalies: case studies
Siberian Traps
Modified after Ivanov and Balyshev, 2005
New models for the melting anomalies: case studies
Siberian Traps
Ivanov et al., 2004; in preparation
New models for the melting anomalies: case studies
Siberian Traps
Ivanov et al., 2004; in preparation
New models for the melting anomalies: case studies
Siberian Traps
Ivanov et al., 2004; in preparation
New models for the melting anomalies: case studies
Siberian Traps
Ivanov et al., 2004; in preparation
Upper Mantle
Transitional zone
Lower Mantle
New models for the melting anomalies: case studies
Siberian Traps
Ivanov et al., 2004; in preparation
New models for the melting anomalies: case studies
Siberian 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 studies
Central Asia
Enriched isotopic signatures require long conservation
of recycled material in the lower mantle and hence
lower mantle plumes
New models for the melting anomalies: case studies
Central Asia
Actually, it does not
Central Asian example
New models for the melting anomalies: case studies
Central 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 studies
Central Asia
Zorin et al., 2004
New models for the melting anomalies: case studies
Central Asia
Zorin et al., 2006 (2 papers in press)
Seismic tomography after model of Zhao, 2004
New models for the melting anomalies: case studies
Demonterova et al., 2005
Central Asia
New models for the melting anomalies: case studies
Demonterova et al., 2005
Central Asia
New models for the melting anomalies: case studies
Demonterova et al., 2005
Central Asia
S=Do/Co
I=[Rbo/Co][1-Po]
New models for the melting anomalies: case studies
Central Asia
Modified after Zorin et al., 2006 (in press)
New models for the melting anomalies: case studies
Central 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 by
plate 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!