HOTSPOT-RIDGE INTERACTION
Colin Devey
GEOMAR Helmholtz Centre for Ocean Research,
Kiel, Germany
Synonyms
Plume-ridge interaction
Definition
The exchange of material (magma, mantle rock) between
an intraplate mantle melting anomaly (hotspot, thought
to be caused in places by the presence of a mantle plume)
and the global spreading ridge system. Evidence for the
interaction is found in the depth of the spreading axis, its
morphology, the chemistry of the lavas (both on the
spreading axis and possibly at the hotspot), and sometimes
by the presence of linear volcanic ridges between spreading axis and hotspot. These linear volcanic ridges generally do not show clear age-progressive volcanism, in
contrast to the volcanoes of the hotspot itself.
Description
As a result of the relative fixity of hotspots with respect to
the moving plates, their distance from active spreading
centers changes over geological time. Depending on the
plate tectonic situation, hotspots can both migrate toward
and away from ridges over time, respectively, weakening
and strengthening the hotspot-ridge interaction. At some
limiting minimum separation (which may be several hundred km and is dependent on whether the two are
approaching or separating from each other), the two begin
to interact. Evidence for hotspot-ridge interaction comes
from both present-day systems and from fossil traces preserved on the seafloor.
In some cases, such as Iceland, the hotspot lies directly
beneath the spreading center (the Mid-Atlantic Ridge),
and there is evidence that the spreading axis regularly relocates via ridge jumps to maintain this situation despite
plate motion (“ridge capture”). In others (e.g., Galapagos
hotspot and Galapagos Spreading Center) there is evidence that the spreading axis is currently moving away
from the hotspot (e.g., Ito and Lin, 1995). It has been proposed (Mittelstaedt et al., 2011) that ridge jumps occur
more regularly at slow spreading rates which may explain,
for example, the tendency for Atlantic hotspots (e.g.,
Azores, St. Helena, Tristan, Bouvet, as well as Iceland)
to cluster near the axis. When the hotspot lies directly on
the spreading axis, mantle upwelling can extend to relatively shallow depths, producing a large volume of
magma. This is at least one factor (in addition to plume
temperature and composition) for Iceland’s large land surface compared to other volcanic ocean islands and has
been suggested as a mechanism by which large oceanic
igneous provinces (such as the Ontong Java-HikurangiManihiki cluster) could have attained their exceptional
size (e.g., Taylor, 2006). Ridge-centered hotspots produce
volcanic trails on both plates on either side of the ridge, as
is seen, for example, in the Greenland-Faroe Ridge, which
the Iceland hotspot has produced since opening of the
North Atlantic, and the dual Carnegie-Cocos Ridges produced by the Galapagos hotspot (e.g., Harpp et al., 2005).
Off-axis hotspots produce variable effects on the
bathymetry of the adjacent axis, related to both the
hotspot-ridge separation distance (the effect falls off with
increasing separation) and the intensity of hotspot volcanism (more productive hotspots have larger effects on
the ridge). The Galapagos hotspot, for example, produces
a large bathymetric anomaly (e.g., Christie et al., 2005) on
the Galapagos Spreading Center (hotspot-ridge separation
150 km). In the past, this hotspot lay directly on the
spreading axis, which led to the construction of a volcanic
ridge (the Cocos Ridge) on the Cocos Plate. The Easter
hotspot, in contrast, has only very limited effect on the
bathymetry of the East Pacific Rise bathymetry
(separation 350 km), and no trace is visible on the opposite
plate (see, e.g., Haase et al., 1996).
The hotspot supplies material to the spreading axis.
Whether this is in the form of direct magma transport or
the flow of mantle material is still unclear (c.f., Braun
and Sohn, 2003; Kokfelt et al., 2005; Stroncik et al.,
2008; Villagomez et al., 2014). The geochemical influence of the hotspot on the ridge often leads to the axis
erupting magmas with compositions more enriched in
mantle-incompatible elements than surrounding segments
of the ridge, although evidence for the eruption of
extremely depleted magmas at both hotspots and their
adjacent axes has also been found (Portnyagin et al.,
2009; Stroncik and Devey, 2011). Several hotspotinfluenced ridges have been found to erupt magmas more
fractionated than basalt – in some cases, these magmas
have compositions very similar to early continental crust
(Haase et al., 2005). Hotspot-ridge interaction also clearly
influences the composition of the hotspot magmas – the
extent to which this influence results from (a) the effects
of lithospheric thickness on depth and degree of melting,
(b) the flow of material from the ridge to the hotspot, or
(c) the consequence of the removal of hotspot material
toward the ridge is hotly debated (Haase et al., 1996; Keller et al., 2000; Stroncik and Devey, 2011)
When the hotspot is close to the ridge, the seafloor separating them is also the site of intense volcanism (e.g.,
Christie et al., 2005; Fretzdorff et al., 1996; Maia et al.,
2000). Sometimes this is manifested as linear volcanic
ridges running between hotspot and ridge (e.g.,
Kopp et al., 2003; Maia et al., 2000) which show no systematic age-distance relationship, in contrast to the
hotspot volcanoes themselves (O’Connor et al., 2001).
Summary
Hotspot-ridge interaction affects large areas of the seafloor, resulting in bathymetric, structural, and geochemical anomalies on both ridge and hotspot.
328
HOTSPOT-RIDGE INTERACTION
Colin Devey
GEOMAR Helmholtz Centre for Ocean Research,
Kiel, Germany
Synonyms
Plume-ridge interaction
Definition
The exchange of material (magma, mantle rock) between
an intraplate mantle melting anomaly (hotspot, thought
to be caused in places by the presence of a mantle plume)
and the global spreading ridge system. Evidence for the
interaction is found in the depth of the spreading axis, its
morphology, the chemistry of the lavas (both on the
spreading axis and possibly at the hotspot), and sometimes
by the presence of linear volcanic ridges between spreading axis and hotspot. These linear volcanic ridges generally do not show clear age-progressive volcanism, in
contrast to the volcanoes of the hotspot itself.
Description
As a result of the relative fixity of hotspots with respect to
the moving plates, their distance from active spreading
centers changes over geological time. Depending on the
plate tectonic situation, hotspots can both migrate toward
and away from ridges over time, respectively, weakening
and strengthening the hotspot-ridge interaction. At some
limiting minimum separation (which may be several hundred km and is dependent on whether the two are
approaching or separating from each other), the two begin
to interact. Evidence for hotspot-ridge interaction comes
from both present-day systems and from fossil traces preserved on the seafloor.
In some cases, such as Iceland, the hotspot lies directly
beneath the spreading center (the Mid-Atlantic Ridge),
and there is evidence that the spreading axis regularly relocates via ridge jumps to maintain this situation despite
plate motion (“ridge capture”). In others (e.g., Galapagos
hotspot and Galapagos Spreading Center) there is evidence that the spreading axis is currently moving away
from the hotspot (e.g., Ito and Lin, 1995). It has been proposed (Mittelstaedt et al., 2011) that ridge jumps occur
more regularly at slow spreading rates which may explain,
for example, the tendency for Atlantic hotspots (e.g.,
Azores, St. Helena, Tristan, Bouvet, as well as Iceland)
to cluster near the axis. When the hotspot lies directly on
the spreading axis, mantle upwelling can extend to relatively shallow depths, producing a large volume of
magma. This is at least one factor (in addition to plume
temperature and composition) for Iceland’s large land surface compared to other volcanic ocean islands and has
been suggested as a mechanism by which large oceanic
igneous provinces (such as the Ontong Java-HikurangiManihiki cluster) could have attained their exceptional
size (e.g., Taylor, 2006). Ridge-centered hotspots produce
volcanic trails on both plates on either side of the ridge, as
is seen, for example, in the Greenland-Faroe Ridge, which
the Iceland hotspot has produced since opening of the
North Atlantic, and the dual Carnegie-Cocos Ridges produced by the Galapagos hotspot (e.g., Harpp et al., 2005).
Off-axis hotspots produce variable effects on the
bathymetry of the adjacent axis, related to both the
hotspot-ridge separation distance (the effect falls off with
increasing separation) and the intensity of hotspot volcanism (more productive hotspots have larger effects on
the ridge). The Galapagos hotspot, for example, produces
a large bathymetric anomaly (e.g., Christie et al., 2005) on
the Galapagos Spreading Center (hotspot-ridge separation
150 km). In the past, this hotspot lay directly on the
spreading axis, which led to the construction of a volcanic
ridge (the Cocos Ridge) on the Cocos Plate. The Easter
hotspot, in contrast, has only very limited effect on the
bathymetry of the East Pacific Rise bathymetry
(separation 350 km), and no trace is visible on the opposite
plate (see, e.g., Haase et al., 1996).
The hotspot supplies material to the spreading axis.
Whether this is in the form of direct magma transport or
the flow of mantle material is still unclear (c.f., Braun
and Sohn, 2003; Kokfelt et al., 2005; Stroncik et al.,
2008; Villagomez et al., 2014). The geochemical influence of the hotspot on the ridge often leads to the axis
erupting magmas with compositions more enriched in
mantle-incompatible elements than surrounding segments
of the ridge, although evidence for the eruption of
extremely depleted magmas at both hotspots and their
adjacent axes has also been found (Portnyagin et al.,
2009; Stroncik and Devey, 2011). Several hotspotinfluenced ridges have been found to erupt magmas more
fractionated than basalt – in some cases, these magmas
have compositions very similar to early continental crust
(Haase et al., 2005). Hotspot-ridge interaction also clearly
influences the composition of the hotspot magmas – the
extent to which this influence results from (a) the effects
of lithospheric thickness on depth and degree of melting,
(b) the flow of material from the ridge to the hotspot, or
(c) the consequence of the removal of hotspot material
toward the ridge is hotly debated (Haase et al., 1996; Keller et al., 2000; Stroncik and Devey, 2011)
When the hotspot is close to the ridge, the seafloor separating them is also the site of intense volcanism (e.g.,
Christie et al., 2005; Fretzdorff et al., 1996; Maia et al.,
2000). Sometimes this is manifested as linear volcanic
ridges running between hotspot and ridge (e.g.,
Kopp et al., 2003; Maia et al., 2000) which show no systematic age-distance relationship, in contrast to the
hotspot volcanoes themselves (O’Connor et al., 2001).
Summary
Hotspot-ridge interaction affects large areas of the seafloor, resulting in bathymetric, structural, and geochemical anomalies on both ridge and hotspot.
328
HOTSPOT-RIDGE INTERACTION