crust of the Kerguelen Plateau, or both (Barling et al.,
1994).
A small subset of seamounts are sea knolls confined to
the forebulge of oceanic plates seaward of trenches; these
have been termed petit spots (e.g., Hirano et al., 2001).
These features rise 100–200 m above surrounding seafloor, with a volume typically <1 km
3
. Lavas from petit
spots are alkaline, and their elemental and isotopic compositions suggest that the magmas originate in the asthenosphere (Hirano et al., 2006).
Little differentiates age-progressive chains of volcanoes from submarine ridges, e.g., the Hawaiian-Emperor
seamount chain consists of the younger Hawaiian Ridge
and the older Emperor seamount chain (Figure 1). Similarly, an age-progressive chain of seamounts in the South
Pacific is known as the Louisville Ridge (Figure 1). While
both the Hawaiian-Emperor seamount chain and Louisville Ridge are intraplate, the tectonic settings of emplacement of other prominent age-progressive submarine
ridges (e.g., Walvis/Rio Grande and Greenland-IcelandFaroes in the Atlantic Ocean, Ninetyeast and ChagosLaccadive/Mascarene in the Indian Ocean) appear to be
on, or proximal to, plate boundaries. The crustal nature –
oceanic or continental – of still other submarine ridges
(e.g., Alpha-Mendeleev in the Arctic Ocean) remains
controversial.
The archetypal Hawaiian-Emperor chain of volcanoes
extends for more than 5,800 km from the active intraplate
submarine volcano of Loihi southeast of the island of
Hawaii to Meiji Seamount on the outer slope of the
Kuril-Kamchatka Trench in the northwest (Figure 1).
The chain includes more than 80 islands, atolls, reefs,
banks, and seamounts. Overall, lavas from the HawaiianEmperor chain show significant heterogeneity, including
tholeiitic and alkalic basalts and their differentiates, and
silica-undersaturated lavas (e.g., Regelous et al., 2003).
In contrast to the Hawaiian-Emperor chain, lavas of the
entirely submarine Louisville seamount chain (“Louisville
Ridge,” Figure 1) are relatively homogeneous. Only alkaline rocks have been dredged and drilled from Louisville
seamounts, and it may be that Louisville shield volcanoes
are produced by massive alkaline volcanism, as opposed
to the tholeiitic shield volcanism characterizing
Hawaiian-Emperor chain volcanoes (e.g., Koppers et al.,
2013).
On the massive end of the scale of intraplate
magmatism lie some oceanic plateaus, one category of
large igneous province (LIP, e.g., Coffin and Eldholm,
1994). Oceanic plateaus constitute a subset of submarine
plateaus; the latter may be continental (e.g., Campbell),
oceanic (e.g., Ontong Java), or hybrid (e.g., Kerguelen)
in crustal nature. The sole oceanic plateau forming today
is Iceland astride the Mid-Atlantic Ridge, so it does not
meet the intraplate criterion. Some ancient oceanic plateaus, e.g., Shatsky in the northwest Pacific Ocean and
the conjugate Ceara/Sierra Leone provinces in the central
Atlantic Ocean, also formed at or near plate boundaries
(e.g., Seton et al., 2012).
The volcanic rocks of many oceanic and hybrid plateaus formed during the Cretaceous Normal Superchron
(~121 to ~83 million years ago), which makes identification of tectonic setting challenging due to the absence of
marine magnetic anomalies in adjacent ocean basins.
These Cretaceous oceanic – Caribbean, Conrad, Crozet,
East Mariana, Hess, Hikurangi, Manihiki, Nauru, Ontong
Java, Pigafetta – and hybrid – Broken, Kerguelen, Madagascar, Naturaliste, Wallaby – plateaus may have formed
proximal or distal to plate boundaries.
Among the best studied of these plateaus, i.e., those
with multiple samples of igneous basement rocks, are
greater Ontong Java (Ontong Java, East Mariana, Nauru,
Pigafetta), the conjugate Manihiki/Hikurangi, and the
Caribbean (Figure 1). Lying in the western equatorial
Pacific Ocean, the greater Ontong Java Plateau, including
the Plateau proper as well as the neighboring East
Mariana, Nauru, and Pigafetta basin flood basalts, encompasses ~4.27 Â 10
6 km
2 , or ~0.8 %, of the Earth’s surface
(Ingle and Coffin, 2004) (Figure 1). Emplaced ~120 million years ago (e.g., Neal et al., 1997; Fitton et al.,
2004), the Ontong Java Plateau appears to have formed
within ~130- to ~160-million-year-old oceanic lithosphere (e.g., Ishikawa et al., 2005), thus qualifying as
intraplate magmatism. The elemental and isotopic geochemistry of greater Ontong Java Plateau tholeiitic lavas
is remarkably homogeneous, suggesting a homogeneous
mantle source (e.g., Fitton et al., 2004).
The conjugate Manihiki and Hikurangi plateaus in the
southwest Pacific Ocean (Figure 1) also formed ~120 million years ago (e.g., Hoernle et al., 2010; Timm et al.,
2011), and it has been proposed that they formed adjacent
to the Ontong Java Plateau (Taylor, 2006). Plate tectonic
reconstructions suggest a plate boundary proximal to
Manihiki and Hikurangi when they formed (e.g., Seton
et al., 2012), casting some doubt as to whether they represent intraplate magmatism. Nevertheless, tholeiitic lavas
of igneous basement of both plateaus show strong elemental and isotopic geochemical similarities to Ontong Java
basalts, suggesting a common mantle source (Hoernle
et al., 2010).
The Caribbean flood basalt province (Figure 1),
consisting of basalts, picrites, and komatiites, formed over
a relatively long time span from 139 to 69 million years
ago, with a major portion emplaced ~90 million years
ago and a secondary peak of volcanism at ~75 million
years ago (e.g., Kerr et al., 1997; Sinton et al., 1998;
Hoernle et al., 2004). Elemental and isotopic geochemistry shows that the two major pulses are largely compositionally distinct, indicating at least two mantle sources
(Hoernle et al., 2004).
Causes of intraplate magmatism
The concept of intraplate magmatism developed at the
same time as the plate tectonic paradigm. Such
magmatism requires an explanation other than the plate
tectonic processes of seafloor spreading and subduction.
374
INTRAPLATE MAGMATISM
1994).
A small subset of seamounts are sea knolls confined to
the forebulge of oceanic plates seaward of trenches; these
have been termed petit spots (e.g., Hirano et al., 2001).
These features rise 100–200 m above surrounding seafloor, with a volume typically <1 km
3
. Lavas from petit
spots are alkaline, and their elemental and isotopic compositions suggest that the magmas originate in the asthenosphere (Hirano et al., 2006).
Little differentiates age-progressive chains of volcanoes from submarine ridges, e.g., the Hawaiian-Emperor
seamount chain consists of the younger Hawaiian Ridge
and the older Emperor seamount chain (Figure 1). Similarly, an age-progressive chain of seamounts in the South
Pacific is known as the Louisville Ridge (Figure 1). While
both the Hawaiian-Emperor seamount chain and Louisville Ridge are intraplate, the tectonic settings of emplacement of other prominent age-progressive submarine
ridges (e.g., Walvis/Rio Grande and Greenland-IcelandFaroes in the Atlantic Ocean, Ninetyeast and ChagosLaccadive/Mascarene in the Indian Ocean) appear to be
on, or proximal to, plate boundaries. The crustal nature –
oceanic or continental – of still other submarine ridges
(e.g., Alpha-Mendeleev in the Arctic Ocean) remains
controversial.
The archetypal Hawaiian-Emperor chain of volcanoes
extends for more than 5,800 km from the active intraplate
submarine volcano of Loihi southeast of the island of
Hawaii to Meiji Seamount on the outer slope of the
Kuril-Kamchatka Trench in the northwest (Figure 1).
The chain includes more than 80 islands, atolls, reefs,
banks, and seamounts. Overall, lavas from the HawaiianEmperor chain show significant heterogeneity, including
tholeiitic and alkalic basalts and their differentiates, and
silica-undersaturated lavas (e.g., Regelous et al., 2003).
In contrast to the Hawaiian-Emperor chain, lavas of the
entirely submarine Louisville seamount chain (“Louisville
Ridge,” Figure 1) are relatively homogeneous. Only alkaline rocks have been dredged and drilled from Louisville
seamounts, and it may be that Louisville shield volcanoes
are produced by massive alkaline volcanism, as opposed
to the tholeiitic shield volcanism characterizing
Hawaiian-Emperor chain volcanoes (e.g., Koppers et al.,
2013).
On the massive end of the scale of intraplate
magmatism lie some oceanic plateaus, one category of
large igneous province (LIP, e.g., Coffin and Eldholm,
1994). Oceanic plateaus constitute a subset of submarine
plateaus; the latter may be continental (e.g., Campbell),
oceanic (e.g., Ontong Java), or hybrid (e.g., Kerguelen)
in crustal nature. The sole oceanic plateau forming today
is Iceland astride the Mid-Atlantic Ridge, so it does not
meet the intraplate criterion. Some ancient oceanic plateaus, e.g., Shatsky in the northwest Pacific Ocean and
the conjugate Ceara/Sierra Leone provinces in the central
Atlantic Ocean, also formed at or near plate boundaries
(e.g., Seton et al., 2012).
The volcanic rocks of many oceanic and hybrid plateaus formed during the Cretaceous Normal Superchron
(~121 to ~83 million years ago), which makes identification of tectonic setting challenging due to the absence of
marine magnetic anomalies in adjacent ocean basins.
These Cretaceous oceanic – Caribbean, Conrad, Crozet,
East Mariana, Hess, Hikurangi, Manihiki, Nauru, Ontong
Java, Pigafetta – and hybrid – Broken, Kerguelen, Madagascar, Naturaliste, Wallaby – plateaus may have formed
proximal or distal to plate boundaries.
Among the best studied of these plateaus, i.e., those
with multiple samples of igneous basement rocks, are
greater Ontong Java (Ontong Java, East Mariana, Nauru,
Pigafetta), the conjugate Manihiki/Hikurangi, and the
Caribbean (Figure 1). Lying in the western equatorial
Pacific Ocean, the greater Ontong Java Plateau, including
the Plateau proper as well as the neighboring East
Mariana, Nauru, and Pigafetta basin flood basalts, encompasses ~4.27 Â 10
6 km
2 , or ~0.8 %, of the Earth’s surface
(Ingle and Coffin, 2004) (Figure 1). Emplaced ~120 million years ago (e.g., Neal et al., 1997; Fitton et al.,
2004), the Ontong Java Plateau appears to have formed
within ~130- to ~160-million-year-old oceanic lithosphere (e.g., Ishikawa et al., 2005), thus qualifying as
intraplate magmatism. The elemental and isotopic geochemistry of greater Ontong Java Plateau tholeiitic lavas
is remarkably homogeneous, suggesting a homogeneous
mantle source (e.g., Fitton et al., 2004).
The conjugate Manihiki and Hikurangi plateaus in the
southwest Pacific Ocean (Figure 1) also formed ~120 million years ago (e.g., Hoernle et al., 2010; Timm et al.,
2011), and it has been proposed that they formed adjacent
to the Ontong Java Plateau (Taylor, 2006). Plate tectonic
reconstructions suggest a plate boundary proximal to
Manihiki and Hikurangi when they formed (e.g., Seton
et al., 2012), casting some doubt as to whether they represent intraplate magmatism. Nevertheless, tholeiitic lavas
of igneous basement of both plateaus show strong elemental and isotopic geochemical similarities to Ontong Java
basalts, suggesting a common mantle source (Hoernle
et al., 2010).
The Caribbean flood basalt province (Figure 1),
consisting of basalts, picrites, and komatiites, formed over
a relatively long time span from 139 to 69 million years
ago, with a major portion emplaced ~90 million years
ago and a secondary peak of volcanism at ~75 million
years ago (e.g., Kerr et al., 1997; Sinton et al., 1998;
Hoernle et al., 2004). Elemental and isotopic geochemistry shows that the two major pulses are largely compositionally distinct, indicating at least two mantle sources
(Hoernle et al., 2004).
Causes of intraplate magmatism
The concept of intraplate magmatism developed at the
same time as the plate tectonic paradigm. Such
magmatism requires an explanation other than the plate
tectonic processes of seafloor spreading and subduction.
374
INTRAPLATE MAGMATISM