Uyeda, S., and Ben-Avraham, Z., 1972. Origin and development of
the Philippine Sea. Nature, 240, 176–178.
Uyeda, S., and Kanamori, H., 1979. Back-arc opening and the mode
of subduction. Journal of Geophysical Research, 84,
1049–1061.
Cross-references
Accretionary Wedges
Active Continental Margins
Cumulates
Earthquakes
Gabbro
Hydrothermalism
Island Arc Volcanism, Volcanic Arcs
Magmatism at Convergent Plate Boundaries
Marginal Seas
Mud Volcano
Oceanic Spreading Centers
Ophiolites
Peridotites
Seamounts
Seismogenic Zone
Serpentinization
Subduction
Subduction Erosion
Transform Faults
INTRAPLATE MAGMATISM
Millard F. Coffin and Joanne M. Whittaker
Institute for Marine and Antarctic Studies, University of
Tasmania, Hobart, TAS, Australia
Definition
Intraplate magmatism constitutes igneous activity distal
from the boundaries of the tectonic plates and is thus considered to be unrelated to the processes of seafloor spreading, subduction, and transform faulting.
Introduction
Intraplate magmatism is pervasive within both oceanic
and continental crust. Expansive spatially and across geologic time, it is complex because of both its causative magmatic processes as well as its interplay with Earth’s mantle
geodynamics and plate tectonic processes. The scale of
intraplate magmatism ranges from large igneous provinces (LIPs) encompassing millions of cubic kilometers
of igneous rock to small individual volcanoes. Similarly,
compositions of intraplate igneous rock span the spectrum
of extrusive compositions between highly mafic and
highly silicic. However, intraplate volcanic rocks are dominantly basaltic and have compositions distinctly different
from those found at “normal” mid-ocean ridges and in
arc-trench systems. Herein we focus on intraplate
magmatism in the oceans that cover 71 % of Earth’s surface. We examine intraplate magmatism both present and
past in the oceans, which has occurred predominantly
within oceanic crust. The geological record of oceanic
crust flooring much of the world’s oceans extends back
to ~200 million years ago, or slightly less than 5 %, of
Earth history.
Tectonic setting
Tectonic setting determines whether or not magmatism is
considered intraplate. Although it may appear relatively
straightforward to distinguish between intraplate
magmatism and plate boundary magmatism, this is certainly not the case. Diffuse zones of plate deformation,
forebulges (flexural bends on subducting plates), and
zones of intraplate extension and convergence complicate
the present-day picture, together with magmatism
exploiting ancient plate boundaries and other zones of
weakness. Moving back through geologic time, identification of plate boundaries and the times when they were
active becomes increasingly more challenging, as does
our knowledge of the geochronology of candidate intraplate igneous rocks, so we focus on the present, augmented by our knowledge of the past 200 million years
in the oceans.
Currently, 25 tectonic plates collectively occupy 97 %
of Earth’s surface (DeMets et al., 2010). Boundaries of
the majority of these are relatively distinct; however, diffuse boundaries characterize portions of the Capricorn,
Caribbean, Lwandle, Macquarie, and Sur plates
(Figure 1). Forebulges, in this case flexural lithospheric
bulges seaward of subduction zone trenches, are common
features throughout the global ocean and are considered to
be intraplate rather than part of a plate boundary. Intraplate
stress can result in zones of extension and convergence,
examples of which are found in the global ocean; these
may or may not develop into plate boundaries.
Morphology and characteristics of oceanic
intraplate magmatism
The scale of intraplate volcanic features in the oceans
ranges over many orders of magnitude, from small volcanoes on the seafloor that rise <100 m above surrounding
seafloor to massive oceanic plateaus with areas exceeding
10
6 km
2 and volumes of igneous rock greater than
10
7 km
3
. Within this continuum are volcanoes rising hundreds to thousands of meters above the ambient seafloor,
linked chains of volcanoes, and submarine ridges, all of
which can have subaerial expressions. Below, we examine
these various features, including key examples, in more
detail.
Individual undersea volcanoes, known as seamounts,
sea knolls, and/or guyots (hereafter all referred to as “seamounts”), are among the most ubiquitous landforms on
Earth (Wessel et al., 2010) and are found across the entire
range of ages of oceanic crust, i.e., from zero age to
approaching 200 million years. Excluding subductionrelated island arc volcanoes but including volcanoes
formed near seafloor spreading centers, Wessel
et al. (2010) predict the population of seamounts in the
372
INTRAPLATE MAGMATISM
the Philippine Sea. Nature, 240, 176–178.
Uyeda, S., and Kanamori, H., 1979. Back-arc opening and the mode
of subduction. Journal of Geophysical Research, 84,
1049–1061.
Cross-references
Accretionary Wedges
Active Continental Margins
Cumulates
Earthquakes
Gabbro
Hydrothermalism
Island Arc Volcanism, Volcanic Arcs
Magmatism at Convergent Plate Boundaries
Marginal Seas
Mud Volcano
Oceanic Spreading Centers
Ophiolites
Peridotites
Seamounts
Seismogenic Zone
Serpentinization
Subduction
Subduction Erosion
Transform Faults
INTRAPLATE MAGMATISM
Millard F. Coffin and Joanne M. Whittaker
Institute for Marine and Antarctic Studies, University of
Tasmania, Hobart, TAS, Australia
Definition
Intraplate magmatism constitutes igneous activity distal
from the boundaries of the tectonic plates and is thus considered to be unrelated to the processes of seafloor spreading, subduction, and transform faulting.
Introduction
Intraplate magmatism is pervasive within both oceanic
and continental crust. Expansive spatially and across geologic time, it is complex because of both its causative magmatic processes as well as its interplay with Earth’s mantle
geodynamics and plate tectonic processes. The scale of
intraplate magmatism ranges from large igneous provinces (LIPs) encompassing millions of cubic kilometers
of igneous rock to small individual volcanoes. Similarly,
compositions of intraplate igneous rock span the spectrum
of extrusive compositions between highly mafic and
highly silicic. However, intraplate volcanic rocks are dominantly basaltic and have compositions distinctly different
from those found at “normal” mid-ocean ridges and in
arc-trench systems. Herein we focus on intraplate
magmatism in the oceans that cover 71 % of Earth’s surface. We examine intraplate magmatism both present and
past in the oceans, which has occurred predominantly
within oceanic crust. The geological record of oceanic
crust flooring much of the world’s oceans extends back
to ~200 million years ago, or slightly less than 5 %, of
Earth history.
Tectonic setting
Tectonic setting determines whether or not magmatism is
considered intraplate. Although it may appear relatively
straightforward to distinguish between intraplate
magmatism and plate boundary magmatism, this is certainly not the case. Diffuse zones of plate deformation,
forebulges (flexural bends on subducting plates), and
zones of intraplate extension and convergence complicate
the present-day picture, together with magmatism
exploiting ancient plate boundaries and other zones of
weakness. Moving back through geologic time, identification of plate boundaries and the times when they were
active becomes increasingly more challenging, as does
our knowledge of the geochronology of candidate intraplate igneous rocks, so we focus on the present, augmented by our knowledge of the past 200 million years
in the oceans.
Currently, 25 tectonic plates collectively occupy 97 %
of Earth’s surface (DeMets et al., 2010). Boundaries of
the majority of these are relatively distinct; however, diffuse boundaries characterize portions of the Capricorn,
Caribbean, Lwandle, Macquarie, and Sur plates
(Figure 1). Forebulges, in this case flexural lithospheric
bulges seaward of subduction zone trenches, are common
features throughout the global ocean and are considered to
be intraplate rather than part of a plate boundary. Intraplate
stress can result in zones of extension and convergence,
examples of which are found in the global ocean; these
may or may not develop into plate boundaries.
Morphology and characteristics of oceanic
intraplate magmatism
The scale of intraplate volcanic features in the oceans
ranges over many orders of magnitude, from small volcanoes on the seafloor that rise <100 m above surrounding
seafloor to massive oceanic plateaus with areas exceeding
10
6 km
2 and volumes of igneous rock greater than
10
7 km
3
. Within this continuum are volcanoes rising hundreds to thousands of meters above the ambient seafloor,
linked chains of volcanoes, and submarine ridges, all of
which can have subaerial expressions. Below, we examine
these various features, including key examples, in more
detail.
Individual undersea volcanoes, known as seamounts,
sea knolls, and/or guyots (hereafter all referred to as “seamounts”), are among the most ubiquitous landforms on
Earth (Wessel et al., 2010) and are found across the entire
range of ages of oceanic crust, i.e., from zero age to
approaching 200 million years. Excluding subductionrelated island arc volcanoes but including volcanoes
formed near seafloor spreading centers, Wessel
et al. (2010) predict the population of seamounts in the
372
INTRAPLATE MAGMATISM