zone rather than a mantle plume. However, Koppers
et al. (2008) obtained
40
Ar–
39
Ar ages of 5 Ma on basalts
dredged from the flanks of Savai’i, which agree well with
the predicted age assuming a lithospheric motion of
7.1 cm/year and a current location of the hot spot beneath
the young, volcanically active seamount Vailulu’u. The
volume of Samoan rejuvenescent volcanism does seem
unusually large; Konter and Jackson (2012) estimate that
it is responsible for up to 2 % of the volume of Savai’i.
It is also unusual in that the post-erosional volcanics do
not have a depleted radiogenic isotope signature (Wright
and White, 1987; Konter and Jackson, 2012).
The two main questions are why does volcanism flair
up again after the volcano has moved off the plume and
what is melting to produce post-erosional magmas? Several ideas have been put forth as to the cause. The numerical model of plume dynamics of Ribe and Christensen
(1999) predicts small secondary melting zone downstream
from the hot spot as a consequence of upwelling and
decompression of the mantle plume as it interacts with
the overlying lithosphere. Jackson and Wright (1970),
ten Brink and Brocher (1987), and Bianco et al. (2005)
have proposed it results from lithospheric flexure caused
by the growth of the next volcano in the chain. Liu and
Chase (1991) proposed that rejuvenescent magmas are
derived from the base of the lithosphere which is
conductively heated by the plume sufficiently to melt to
a small degree.
Because rejuvenescent lavas are isotopically distinct
from the shield phase lavas, they must have a different
source. Chen and Frey (1983) suggested the source was
oceanic lithosphere, but in detail the isotope and trace element systematics are inconsistent with this hypothesis
(Yang et al., 2003; White, 2010). White and Duncan
(1996) and Fekiacova et al. (2007) suggested it was deep
mantle viscously entrained by the plume, and geodynamic
models do indeed show a region of melting deep in the
plume extending well downstream of the principal melting
regime (e.g., Hofmann and Farnetani, 2013; Figure 1).
Bianco et al. (2005) and Paul et al. (2005) proposed that
the Hawaiian and Reunion mantle plumes, respectively,
are lithologically heterogeneous with a relatively
incompatible-element-enriched mafic component embedded within a depleted peridotite. According to these
models, the pyroxenite melts more or less completely in
the plume stem as it rises beneath the growing shield volcano. Subsequently, due either to lithospheric flexure or
buoyant lateral spreading of the plume, small degree melts
of the depleted peridotite are generated and erupt as the
post-erosional lavas. Moore et al. (2011) proposed a variant of the Chen and Frey hypothesis in which pyroxenite
veins form in the lowermost lithosphere as early shieldbuilding stage melts react with it when it is still cold.
Eventually, conductive heating by the plume causes these
veins to melt to a small degree (Gurriet, 1987), producing
the rejuvenescent magmas. Except for Samoa, where lithospheric flexure appears to be the cause, no consensus has
formed around any of these hypotheses.
Summary
Hot spots are the surface manifestation of mantle plumes.
This hypothesis, proposed by Morgan (1971) to explain
Wilson’s “hot spots,” was initially controversial, but over
the last 40 years, a wealth of geophysical, geochemical,
and petrological data now place it on firm ground. Oceanic
island chains are located on bathymetric “swells,” which
allow estimates of the buoyancy fluxes of the plumes
(Davies, 1988; Sleep, 1990). The total heat flux carried
by plumes is about 10 % of the total mantle heat flux, indicating that plumes are a secondary feature of mantle convection, with plate tectonics being the dominant one.
Estimated buoyancy fluxes correlate with upwelling ratios
estimated from (
230
Th/
238 U) ratios in the lavas (Bourdon
et al., 2006). Regions of slow seismic velocity, indicative
of high temperatures and extending into the deep mantle
and the base of the mantle in many cases, have been found
under most of the oceanic hot spots (Montelli et al., 2006).
Consistent with this, petrological studies demonstrate that
the potential temperatures of the mantle from which OIB
are generated are some 100–300
C hotter than ambient
asthenosphere (e.g., Putirka et al., 2007). Isotope and trace
element geochemistry reveal that plumes contain a variety
of materials originating on or near the Earth’s surface that
have been recycled into the deep mantle through subduction, subduction erosion, or lower crustal foundering.
Many plumes also appear to sample very primitive material, which may have remained essentially unprocessed
since the Earth’s earliest days.
Bibliography
Abouchami, W., Hofmann, A. W., Galer, S. J. G., Frey, F. A., Eisele,
J., and Feigenson, M., 2005. Lead isotopes reveal bilateral asymmetry and vertical continuity in the Hawaiian mantle plume.
Nature, 434(7035), 851–856.
Allègre, C. J., and Turcotte, D. L., 1986. Implications of a two component marble-cake mantle. Nature, 323, 123–127.
Anderson, D. L., 2000. The thermal state of the upper mantle; No
role for mantle plumes. Geophysical Research Letters, 27(22),
3623–3626, doi:10.1029/2000gl011533.
Ballmer, M. D., van Hunen, J., Ito, G., Tackley, P. J., and Bianco,
T. A., 2007. Non-hotspot volcano chains originating from
small-scale sublithospheric convection. Geophysical Research
Letters, 34(23), L23310, doi:10.1029/2007gl031636.
Bianco, T. A., Ito, G., Becker, J. M., and Garcia, M. O., 2005. Secondary Hawaiian volcanism formed by flexural arch decompression. Geochemistry, Geophysics, Geosystems, 6(8), Q08009,
doi:10.1029/2005gc000945.
Blichert-Toft, J., Frey, F., and Albarede, F., 1999. Hf isotope evidence for pelagic sediments in the source of Hawaiian basalts.
Science, 285, 879–882.
Bourdon, B., Ribe, N., Stracke, A., Saal, A., and Turner, S. P., 2006.
Insights into the dynamics of mantle plumes from uranium-series
geochemistry. Nature, 444, 713–717, doi:10.1038/nature05341.
Bryce, J. C., DePaolo, D. J., and Lassiter, J. C., 2005. Geochemical
structure of the Hawaiian plume: Sr, Nd, and Os isotopes in the
2.8 km HSDP-2 section of the Mauna Kea volcano. Geochemistry, Geophysics, Geosystems, 6, doi:10.1029/2004GC000809.
Cabral, R. A., Jackson, M. G., Rose-Koga, E. F., Koga, K. T.,
Whitehouse, M. J., Antonelli, M. A., Farquhar, J., Day,
J. M. D., and Hauri, E. H., 2013. Anomalous sulphur isotopes
324
HOT SPOTS AND MANTLE PLUMES
et al. (2008) obtained
40
Ar–
39
Ar ages of 5 Ma on basalts
dredged from the flanks of Savai’i, which agree well with
the predicted age assuming a lithospheric motion of
7.1 cm/year and a current location of the hot spot beneath
the young, volcanically active seamount Vailulu’u. The
volume of Samoan rejuvenescent volcanism does seem
unusually large; Konter and Jackson (2012) estimate that
it is responsible for up to 2 % of the volume of Savai’i.
It is also unusual in that the post-erosional volcanics do
not have a depleted radiogenic isotope signature (Wright
and White, 1987; Konter and Jackson, 2012).
The two main questions are why does volcanism flair
up again after the volcano has moved off the plume and
what is melting to produce post-erosional magmas? Several ideas have been put forth as to the cause. The numerical model of plume dynamics of Ribe and Christensen
(1999) predicts small secondary melting zone downstream
from the hot spot as a consequence of upwelling and
decompression of the mantle plume as it interacts with
the overlying lithosphere. Jackson and Wright (1970),
ten Brink and Brocher (1987), and Bianco et al. (2005)
have proposed it results from lithospheric flexure caused
by the growth of the next volcano in the chain. Liu and
Chase (1991) proposed that rejuvenescent magmas are
derived from the base of the lithosphere which is
conductively heated by the plume sufficiently to melt to
a small degree.
Because rejuvenescent lavas are isotopically distinct
from the shield phase lavas, they must have a different
source. Chen and Frey (1983) suggested the source was
oceanic lithosphere, but in detail the isotope and trace element systematics are inconsistent with this hypothesis
(Yang et al., 2003; White, 2010). White and Duncan
(1996) and Fekiacova et al. (2007) suggested it was deep
mantle viscously entrained by the plume, and geodynamic
models do indeed show a region of melting deep in the
plume extending well downstream of the principal melting
regime (e.g., Hofmann and Farnetani, 2013; Figure 1).
Bianco et al. (2005) and Paul et al. (2005) proposed that
the Hawaiian and Reunion mantle plumes, respectively,
are lithologically heterogeneous with a relatively
incompatible-element-enriched mafic component embedded within a depleted peridotite. According to these
models, the pyroxenite melts more or less completely in
the plume stem as it rises beneath the growing shield volcano. Subsequently, due either to lithospheric flexure or
buoyant lateral spreading of the plume, small degree melts
of the depleted peridotite are generated and erupt as the
post-erosional lavas. Moore et al. (2011) proposed a variant of the Chen and Frey hypothesis in which pyroxenite
veins form in the lowermost lithosphere as early shieldbuilding stage melts react with it when it is still cold.
Eventually, conductive heating by the plume causes these
veins to melt to a small degree (Gurriet, 1987), producing
the rejuvenescent magmas. Except for Samoa, where lithospheric flexure appears to be the cause, no consensus has
formed around any of these hypotheses.
Summary
Hot spots are the surface manifestation of mantle plumes.
This hypothesis, proposed by Morgan (1971) to explain
Wilson’s “hot spots,” was initially controversial, but over
the last 40 years, a wealth of geophysical, geochemical,
and petrological data now place it on firm ground. Oceanic
island chains are located on bathymetric “swells,” which
allow estimates of the buoyancy fluxes of the plumes
(Davies, 1988; Sleep, 1990). The total heat flux carried
by plumes is about 10 % of the total mantle heat flux, indicating that plumes are a secondary feature of mantle convection, with plate tectonics being the dominant one.
Estimated buoyancy fluxes correlate with upwelling ratios
estimated from (
230
Th/
238 U) ratios in the lavas (Bourdon
et al., 2006). Regions of slow seismic velocity, indicative
of high temperatures and extending into the deep mantle
and the base of the mantle in many cases, have been found
under most of the oceanic hot spots (Montelli et al., 2006).
Consistent with this, petrological studies demonstrate that
the potential temperatures of the mantle from which OIB
are generated are some 100–300
C hotter than ambient
asthenosphere (e.g., Putirka et al., 2007). Isotope and trace
element geochemistry reveal that plumes contain a variety
of materials originating on or near the Earth’s surface that
have been recycled into the deep mantle through subduction, subduction erosion, or lower crustal foundering.
Many plumes also appear to sample very primitive material, which may have remained essentially unprocessed
since the Earth’s earliest days.
Bibliography
Abouchami, W., Hofmann, A. W., Galer, S. J. G., Frey, F. A., Eisele,
J., and Feigenson, M., 2005. Lead isotopes reveal bilateral asymmetry and vertical continuity in the Hawaiian mantle plume.
Nature, 434(7035), 851–856.
Allègre, C. J., and Turcotte, D. L., 1986. Implications of a two component marble-cake mantle. Nature, 323, 123–127.
Anderson, D. L., 2000. The thermal state of the upper mantle; No
role for mantle plumes. Geophysical Research Letters, 27(22),
3623–3626, doi:10.1029/2000gl011533.
Ballmer, M. D., van Hunen, J., Ito, G., Tackley, P. J., and Bianco,
T. A., 2007. Non-hotspot volcano chains originating from
small-scale sublithospheric convection. Geophysical Research
Letters, 34(23), L23310, doi:10.1029/2007gl031636.
Bianco, T. A., Ito, G., Becker, J. M., and Garcia, M. O., 2005. Secondary Hawaiian volcanism formed by flexural arch decompression. Geochemistry, Geophysics, Geosystems, 6(8), Q08009,
doi:10.1029/2005gc000945.
Blichert-Toft, J., Frey, F., and Albarede, F., 1999. Hf isotope evidence for pelagic sediments in the source of Hawaiian basalts.
Science, 285, 879–882.
Bourdon, B., Ribe, N., Stracke, A., Saal, A., and Turner, S. P., 2006.
Insights into the dynamics of mantle plumes from uranium-series
geochemistry. Nature, 444, 713–717, doi:10.1038/nature05341.
Bryce, J. C., DePaolo, D. J., and Lassiter, J. C., 2005. Geochemical
structure of the Hawaiian plume: Sr, Nd, and Os isotopes in the
2.8 km HSDP-2 section of the Mauna Kea volcano. Geochemistry, Geophysics, Geosystems, 6, doi:10.1029/2004GC000809.
Cabral, R. A., Jackson, M. G., Rose-Koga, E. F., Koga, K. T.,
Whitehouse, M. J., Antonelli, M. A., Farquhar, J., Day,
J. M. D., and Hauri, E. H., 2013. Anomalous sulphur isotopes
324
HOT SPOTS AND MANTLE PLUMES