a brief idea about worlds various hotspots, hotspot tracks , their distribution and occurrences

1. Presented by-
Barun Bedanta Sahoo
M.Tech 4th sem
Reg. No- Y16251021

2. Contents
1.Introduction
 What is mantle plume ?
 What is hotspot ?
 How mantle plumes are related to hotspots ?
2.Characteristics of hotspots
3. Hotspot tracks
4. Distribution of hotspots and hotspot tracks around the
world
5.The plume model
6.Hotspots Swells
7.Distinct geochemical signature
8.Association with flood basalt
9.The fixity of the hotspots
10.Conclusion

3. 1.Introduction
 What is mantle plume ?
 Mantle plumes appear to be long, nearly vertical columns of hot,
upwelling materials that buoyantly rise from deep in the mantle,
first proposed by J Tuzo Wilson in 1963.
 A mantle plume is posited to exist where hot rock nucleates at the
core-mantle boundary and rises through the Earth's mantle
becoming a diapir in the Earth's crust.
 What is hotspot ?
 These are the volcanic regions thought to be fed by the underlying
mantle . Eg. Hawaiian island
 Their position on the Earth’s surface is independent of tectonic
plate boundary.

4.  How mantle plumes are related to hotspots ?
 Mantle plumes are areas where heat and/or rocks in the mantle
are rising towards the surface. A hotspot is the surfacial
expression for mantle plumes .
 About 95% of the world’s volcanoes are located near the
boundaries of tectonic plates. The other 5% are thought to be
associated with mantle plumes and hot spots.
(Generation of hotspots and mantle plumes, www.google.com/wiki)

5. 2.Chacateristic features of hotspots
 In ocean basins, hotspots form topographic highs of 500-1200 m with
typical widths of 1000-1500 km. These highs are probably indirect
manifestations of ascending mantle plumes.
 Many hotspots are capped by active or recently active volvcanoes.
Examples are Hawaii and Yellowstone Park in the western United
States.
 Most oceanic hotspots are characterized by gravity highs reflecting
the rise of more dense material from the mantle. Some, however,
have gravity lows.
 One or two aseismic ridges of mostly extinct volcanic chains lead
away from many oceanic hotspots.
 Most hotspots have high heat flow , probably reflecting a mantle
plume at depth.

6. 3.Hotspot tracks
 In continental areas, the age of magmatism and deformation may
increase with distance from a hotspot. These features are known as
hotspot tracks.
 Chains of seamounts and volcanic islands are common in the pacific
basin, and include such well-known island chains as Hawaiian-
Emperor Line, Society and Austral islands, all of which are subparallel
to either the Emperor or Hawaiian chains and approximately
perpendicular to the axis of East Pacific Rise.
 The life span of hotspots vary and depend on such parameters as
plume size and tectonic environment into which plume is emplaced.
 In the pacific ocean, three volcanic chains were generated by
hotspots between 70 and 25 Ma, whereas twelve chains have been
generated in the last 25 My.

7. (Major hotspot tracks in the world,www.gooogle.com/wiki)

8.  Isotopic dates demonstrate that the focus of volcanism in the
Hawaiian chain has migrated to the southeast at a linear rate
about 10 cm/y for the last 30 My.
(Linear increase of ages with distance along the Hawaii-
Emperor chain, hilo.hawaii.edu/~kenhon/GEOL205)

9.  Similar linear decrease in the age of the volcanism occur towards
the south-east in the Marquesas, Society, and Austral island in the
south pacific, with rates of migration of the order of 11cm/y, and in
the Pratt-Welker seamount chain in the Gulf of Alaska at a rate
about 4 cm/y.
(Gradual decrease in elevation with increasing distance from the active
volcano,www.google.com/wiki)

10. 4.Distribution of hotspots and
hotspot tracks around the world
Hotspot tracks
hotspots
(www.googe.com/wiki)

11. Table . Hot Spot Locations
Hot Spot Overlying Plate Latitude Longitude
(degree) (degree)
Hawaii Pacific 20 −157
Samoa Pacific −13 −173
St. Helena Africa −14 −6
Bermuda N. America 33 −67
Cape Verde Africa 14 −20
Pitcairn Pacific −26 −132
MacDonald Pacific −30 −140
Marquesas Pacific −10 −138
Tahiti Pacific −17 −151
Easter Pac-Naz −27 −110
Reunion Indian −20 55
Yellowstone N. America 43 −111
Galapagos Nazca 0 −92
Juan Fernandez Nazca −34 −83
Ethiopia Africa 8 37
Ascencion S. Am-Afr −8 −14
Afar Africa 10 43
Azores Eurasia 39 −28
Iceland N. Am-Eur 65 −20
Madeira Africa 32 −18
(After Crough and Jurdy (1980).,www.google.com/wiki/blogspot)

12.  Somewhere between 40 and 150 active hotspots have been described
on the Earth.
 The best documented hotspots have rather a irregular distribution
occurring in both oceanic and continental areas.
 Some occur on or near the ocean ridges, such as Iceland. St.Halena
and Tristan in the Atlantic basin while others occur near the centres of
plates such as, such as Hawaii.

13. 5.The plume model
Morgan’s plume model (Morgan,
1971):
 Volcanic islands are produced by
plumes rising through the mantle.
 The plumes come from the lower
mantle - and are therefore fixed.
 Plume flow derives the plates.
(Schematic illustrations for the plume model.,www.google.com/wiki)

14. Seismic topography-
Seismic images suggest
that some mantle plumes
originate at lower mantle.

15. Contd…
 If all hotspots have been remained fixed with respect to each other, it
should be possible to superimpose the same hotspots in their
present position on their predicted positions at other times in the
last 150-200 my.
 However, except for hotspots in the near proximity of each other or
on adjacent plates, its not possible to do this, suggesting that
hotspots move in the upper mantle (Duncan and Richards,1991)
 In comparing Atlantic with Pacific hotspots, there are significant
differences between calculated and observed hotspot tracks (Molnar
and Stock, 1987).
 Rates of interplate hotspot motion, however, are more than an
order of magnitude less than plate velocities. For instance, using
paleolatitudes deduced from seamounts, Tarduno and Gee (1995)
show that Pacific hotspots have moved relative to Atlantic hotspots
at a rate of only 30 mm/y.

16. 6.Hotspot swells
 Most hotspots are associated
with topographic swells. Hot
spot swells are regional
topographic highs with widths of
about 1,000km and up to 3 km of
anomalous elevation. The swell
associated with the Hawaiian hot
spot is illustrated in Figure.
 The swell is roughly parabolic in
planform and it extends upstream
of the active hot spot, i.e., toward
the spreading center of the East
Pacific Rise. The excess elevation
associated with the swell decays
rather slowly down the track of
the hot spot

17.  There is considerable observational evidence that the topography of
hot spot swells is directly associated with a geoid anomaly (Haxby and
Turcotte, 1978).
 This correspondence is strong evidence that the excess topography
and mass of the swell are compensated at depth by anomalously
light, possibly hot mantle rock.
 One model for isostatic compensation assumes horizontal variations
in density over a prescribed depth ’W’, the so-called Pratt
compensation.
 The variable density ρp is related to the elevation h above the
adjacent ocean basins by
ρp = ρ0W + ρwh
W + h
where ρ0 = reference density corresponding to zero elevation,
ρw = is seawater density,
W = depth of compensation

18.  With the ocean basin as reference, the geoid anomaly and associated
with the compensated topography is-
 The geoid anomaly is linearly dependent on the topography so that
the local geoid to topography ratio should be a constant for each
swell.

19. 7.Distinct geochemical signature
 The content of incompatible
elements is by 1 to 2 orders
of magnitude higher in
Ocean Island basalt (OIB, e.g.
Hawaii, EM-1 and HIMU)
than it is in Mid-Oceanic
Ridge Basalt (MORB).
 This implies different
reservoirs for OIB and MORB.
(Figure from Hofmann ,1977.,
hilo.hawaii.edu/~kenhon/GEOL205)

20.  The position of the OIB
between MORB and
continental crust suggests that
OIB source may be the result
of back mixing of continental
material into the mantle.
 How different chemical
reservoirs may still exist if the
mantle is undergoing global
mixing is yet an open
question.
(Figure from Hofmann ,1977.,
hilo.hawaii.edu/~kenhon/GEOL205)

21. 8.Association with flood basalt
 Morgan, in 1981, pointed out that a number of hotspot tracks originate in flood
basalt* provinces. He explained that flood basalt was produced from a plume
head arriving at the base of the lithosphere.
(Flood basalts of the world., www.google.com/wiki)

22.  Flood basalt are the largest known volcanic eruptions in the geologic record, and
typically comprise basalt of the order of 1 km thick over an area up to 2000 km
across.
 The association of the Deccan
trap in India with the Reunion
hotspot track.
 The flood basalt eruption is due
to the arrival of the plume
head, and the hotspot track is
formed by the plume tail.
(Figure from White and McKenzie, 1989)
(Figure from Dynamic Earth by G.F. Davies)

23. 9.The fixity of hotspots
 Paleo-magnetic data
strongly suggests that
all of the lava
solidified at 19.5
degrees north
latitude, precisely the
latitude of the
hotspot today. At
least with respect to
latitude it would
seem that the
Hawaiian hotspot has
been nearly fixed for
at least the past 65
million years.
(Paleomagnetic determination of hotspot
location.,/wiki/blogspot)

24.  That portions of island
chains of similar age are
parallel to each other
suggests that the
hotspots themselves
remain mostly fixed with
respect to each other,
otherwise the chains
might be expect to trend
in different directions as
the plumes generating
them moved
independently.
Contd…
(A closer look at the Pacific
hilo.hawaii.edu/~kenhon/GEOL205)

25. 10.Conclusion
 From the foregoing, it should be clear that, like the theory of
plate tectonics, the model of a mantle plume is a simple but
powerful concept
 It explains much of the geologic activity in the central parts of
plates that never seemed to fit a simple interpretation of plate
tectonics.
 Volcanic islands, rifts in continents, flood basalts, and
continental calderas find explanations in the mantle plume
model. Recently, mantle plumes have been used to explain
another class of phenomena, including climate change, mass
extinctions, and even changes in Earth’s magnetic field.

26. 1.Condie, K. C. 2001. Mantle Plumes and Their Record in Earth
History. New York: Cambridge University Press.
2.Duncan, R. A., and M. A. Richards. 1991. Hotspots, mantle
plumes, flood basalts, and true polar wander. Reviews of
Geophysics
29:31–50.
3.Hill, R. I., I. H. Campbell,G. F. Davies, and R.W. Griffiths. 1992.
4.Mantle plumes and continental tectonics. Science
256:186–193.
5.Larson, R. L. 1995.The mid-Cretaceous superplume episode.
Scientific American 272(2):82–86.
6.Smith, R. L., and L.W. Braille. 1994.The Yellowstone hotspot.
7.Journal of Volcanology and Geothermal Research
61:121–127.
8.Earth’s Dynamic Systems Website- www.prenhall.com/hamblin
References

27. Thank you….