Cross-references
Active Continental Margins
Anoxic Oceans
Black and White Smokers
Chemosynthetic Life
Events
Explosive Volcanism in the Deep Sea
Gravity Field
Guyot, Atoll
Hot Spots and Mantle Plumes
Hydrothermal Plumes
Hydrothermal Vent Fluids (Seafloor)
Hydrothermalism
Island Arc Volcanism, Volcanic Arcs
Magmatism at Convergent Plate Boundaries
Marginal Seas
Marine Impacts and Their Consequences
Mid-ocean Ridge Magmatism and Volcanism
Ocean Drilling
Oceanic Plateaus
Oceanic Rifts
Oceanic Spreading Centers
Ophiolites
Paleophysiography of Ocean Basins
Plate Motion
Plate Tectonics
Pull-apart Basins
Reflection/Refraction Seismology
Subduction
Submarine Lava Types
Transform Faults
Triple Junctions
Volcanism and Climate
Volcanogenic Massive Sulfides
Wilson Cycle
ISLAND ARC VOLCANISM, VOLCANIC ARCS
Jim Gill
Earth & Planetary Sciences, University of California,
Santa Cruz, CA, USA
Synonyms
Arc magmatism; Magmatism at convergent plate boundaries; Subduction zone magmatism
Definition
Island arcs are the marine subset of currently active or formerly active volcanoes located near the boundary between
two converging tectonic plates (see Figure 2 in Stern,
Magmatism at Convergent Plate Boundaries). Convergence results in the denser plate being thrust (subducted)
beneath the rigid overlying plate creating an arcuateshaped plate boundary on a spherical Earth that is usually
marked by an oceanic trench. The volcanoes are located
150–350 km away from the trench on the overlying plate
and define an arc in plan view (Frank, 1968). When the
crust of the overlying plate is less than ~25 km thick, most
of the volcanoes lie below sea-level. Only the largest volcanoes form islands, which, therefore, constitute an island
arc. A similar distribution of subduction-related volcanoes
also characterizes active continental margins where the
crust of the overlying plate is thicker and subaerial so that
the volcanoes are not islands (e.g., in western North, Central, and South America; Kamchatka, Russia), but the general processes are similar. “Volcanic arc” refers to the
volcanoes produced by subduction in both settings.
Characteristics of island arcs
Almost 80 % of the active subaerial volcanoes on Earth lie
within 500 km of a convergent plate boundary and, therefore, are “island arc volcanoes.” Their lavas range from
basalt to rhyolite. The rock type “andesite,” named for
the Andes mountains in South America, occurs at about
80 % of these volcanoes. Therefore, volcanism in island
arcs is more andesitic than in other tectonic environments
on Earth, which are mostly basaltic. Because average continental crust is broadly andesitic in composition, continental crust is either created or recycled or both by
island arc magmatism. And because modern plate tectonics is unique to Earth within our solar system, so also are
arc volcanism and continental crust of andesitic
composition.
Most active island arc volcanoes lie 50–100 km apart
and 125 Æ 30 km above the underlying earthquakes that
occur near the top of the subducting plate (the WadatiBenioff-Zone). Most individual arcs (see Figure 2 in
Stern, Magmatism at Convergent Plate Boundaries, for
their names and distribution) differ from one another by
the pairing of the converging plates, although some continuous plate boundaries are conventionally divided into
two or more arcs by a morphological contrast in the upper
plate (e.g., Kermadec vs. Tonga, Mariana vs. Bonin and
Izu, Sunda vs. Banda). Within any one arc, the volcanoes
are remarkably linear over distances of several hundred
kilometers subparallel to, but displaced from, the plate
boundary. This line often is called the volcanic or magmatic front, which is the locus of volcanoes closest to
the convergent plate boundary.
All of the magma types in island arcs are characterized
by distinctive ratios of trace elements and isotopes as the
result of recycling material from the underthrust plate.
More-fluid-mobile elements (e.g., Sr and Pb) are enriched
in arc magmas relative to less-fluid-mobile elements (e.g.,
REE), and the isotopic compositions of Sr and Pb are more
radiogenic, especially relative to the isotopic composition
of Nd, a REE.
Arc crust
The seismically best-imaged island arc crust and upper
mantle are at the Izu-Bonin-Mariana and Aleutian arcs
ISLAND ARC VOLCANISM, VOLCANIC ARCS
379
Active Continental Margins
Anoxic Oceans
Black and White Smokers
Chemosynthetic Life
Events
Explosive Volcanism in the Deep Sea
Gravity Field
Guyot, Atoll
Hot Spots and Mantle Plumes
Hydrothermal Plumes
Hydrothermal Vent Fluids (Seafloor)
Hydrothermalism
Island Arc Volcanism, Volcanic Arcs
Magmatism at Convergent Plate Boundaries
Marginal Seas
Marine Impacts and Their Consequences
Mid-ocean Ridge Magmatism and Volcanism
Ocean Drilling
Oceanic Plateaus
Oceanic Rifts
Oceanic Spreading Centers
Ophiolites
Paleophysiography of Ocean Basins
Plate Motion
Plate Tectonics
Pull-apart Basins
Reflection/Refraction Seismology
Subduction
Submarine Lava Types
Transform Faults
Triple Junctions
Volcanism and Climate
Volcanogenic Massive Sulfides
Wilson Cycle
ISLAND ARC VOLCANISM, VOLCANIC ARCS
Jim Gill
Earth & Planetary Sciences, University of California,
Santa Cruz, CA, USA
Synonyms
Arc magmatism; Magmatism at convergent plate boundaries; Subduction zone magmatism
Definition
Island arcs are the marine subset of currently active or formerly active volcanoes located near the boundary between
two converging tectonic plates (see Figure 2 in Stern,
Magmatism at Convergent Plate Boundaries). Convergence results in the denser plate being thrust (subducted)
beneath the rigid overlying plate creating an arcuateshaped plate boundary on a spherical Earth that is usually
marked by an oceanic trench. The volcanoes are located
150–350 km away from the trench on the overlying plate
and define an arc in plan view (Frank, 1968). When the
crust of the overlying plate is less than ~25 km thick, most
of the volcanoes lie below sea-level. Only the largest volcanoes form islands, which, therefore, constitute an island
arc. A similar distribution of subduction-related volcanoes
also characterizes active continental margins where the
crust of the overlying plate is thicker and subaerial so that
the volcanoes are not islands (e.g., in western North, Central, and South America; Kamchatka, Russia), but the general processes are similar. “Volcanic arc” refers to the
volcanoes produced by subduction in both settings.
Characteristics of island arcs
Almost 80 % of the active subaerial volcanoes on Earth lie
within 500 km of a convergent plate boundary and, therefore, are “island arc volcanoes.” Their lavas range from
basalt to rhyolite. The rock type “andesite,” named for
the Andes mountains in South America, occurs at about
80 % of these volcanoes. Therefore, volcanism in island
arcs is more andesitic than in other tectonic environments
on Earth, which are mostly basaltic. Because average continental crust is broadly andesitic in composition, continental crust is either created or recycled or both by
island arc magmatism. And because modern plate tectonics is unique to Earth within our solar system, so also are
arc volcanism and continental crust of andesitic
composition.
Most active island arc volcanoes lie 50–100 km apart
and 125 Æ 30 km above the underlying earthquakes that
occur near the top of the subducting plate (the WadatiBenioff-Zone). Most individual arcs (see Figure 2 in
Stern, Magmatism at Convergent Plate Boundaries, for
their names and distribution) differ from one another by
the pairing of the converging plates, although some continuous plate boundaries are conventionally divided into
two or more arcs by a morphological contrast in the upper
plate (e.g., Kermadec vs. Tonga, Mariana vs. Bonin and
Izu, Sunda vs. Banda). Within any one arc, the volcanoes
are remarkably linear over distances of several hundred
kilometers subparallel to, but displaced from, the plate
boundary. This line often is called the volcanic or magmatic front, which is the locus of volcanoes closest to
the convergent plate boundary.
All of the magma types in island arcs are characterized
by distinctive ratios of trace elements and isotopes as the
result of recycling material from the underthrust plate.
More-fluid-mobile elements (e.g., Sr and Pb) are enriched
in arc magmas relative to less-fluid-mobile elements (e.g.,
REE), and the isotopic compositions of Sr and Pb are more
radiogenic, especially relative to the isotopic composition
of Nd, a REE.
Arc crust
The seismically best-imaged island arc crust and upper
mantle are at the Izu-Bonin-Mariana and Aleutian arcs
ISLAND ARC VOLCANISM, VOLCANIC ARCS
379