ductile transition zone in the lithosphere. Water’s contribution to metamorphism
means that progressively less water will remain for penetration in the deep mantle.
Heating and dehydration during the metamorphism of the subducting oceanic slabs
will give rise to submarine as well as island arc explosive volcanism. Some
examples of the most devastating subaerial volcanic eruptions such as the Krakatau volcano (Indonesia) in 1883, Tambora (Indonesia) in 1815, El Chichon
(Mexico) in 1982, Ruiz (Columbia) in 1985, and Mont Pelée (Martinique) in 1902
were the result of subduction processes at plate convergence areas (See Chap. 5).
The formation of volcanoes and the production of earthquakes along subduction
plate margins have a common origin. The loci of the major earthquakes are
clustered in the Benioff zone during the breaking up of a slab penetrating into the
Earth’s mantle below 50 km depth at a variable angle of about 20–50°. These deep
earthquakes often occur in the marginal basins at a distance (300–1000 km) from
the trenches. In the Indonesian region, the epicenters of deep earthquakes are often
located 500–600 km north of the Java trench. The strength is most intense in the
rigid lithosphere and vanishes slowly at depth within the mantle. In the immediate
vicinity of the Sumatra-Java (Indonesian) trench system, the greatest earthquakes
are shallow due to a low angle thrust during the breaking of the slabs (Kanamori
1971). The World’s most active earthquake regions are found in the Pacific convergence margins, which are rimed by deep trenches and arc volcanism.
During the Cenozoic period (\50 million years ago), the Pacific plate converged in the west at contact with the Asian Plate, and on the south at contact with
the Indian-Australia-New-Guinean plates that were moving northward. The areas
of Eastern Australia as well as New Guinea and Indonesia have all been affected
by such plate rearrangements. Earlier, during the late Paleozoic ([250 million
ago) and Triassic (200–250 Ma) periods, the granitic and volcanic terrain of the
Eastern Australia-New Guinea-Indonesian regions (including the Sumatra-Java
area) were separated from the Indian Ocean by a deep trench, with a depth of about
6000 m, bordering the islands of Java and Sumatra in Indonesia. Convergence of
the Pacific plate has created one of the World’s longest and deepest subducting
trenches. An example of this type of system of Pacific plate convergence and
subduction is seen on the Tonga-Kermadec volcanic arc and trench.
Tonga-Kermadec Volcanic Arc
The Tonga-Kermadec volcanic arc system is the locus of volcanic activity related
to the convergence of two plates: the Pacific and the Indo-Australian plates. The
Tonga-Kermadec system is 2,530 km long, making it one of the longest, continuous intra-oceanic arcs in the World. It exists in an area going from New Zealand
to the island of Samoa near latitude 15°S (de Ronde et al. 2005; Garry Massoth
2005 personal communication). This region is marked by an extensive felsic type
(rhyolite) of volcanism associated with considerable amounts of silica-enriched
products (Bloomer et al. 1994). The subducting plate is nearly perpendicular to the
350
10 Subduction Zones
means that progressively less water will remain for penetration in the deep mantle.
Heating and dehydration during the metamorphism of the subducting oceanic slabs
will give rise to submarine as well as island arc explosive volcanism. Some
examples of the most devastating subaerial volcanic eruptions such as the Krakatau volcano (Indonesia) in 1883, Tambora (Indonesia) in 1815, El Chichon
(Mexico) in 1982, Ruiz (Columbia) in 1985, and Mont Pelée (Martinique) in 1902
were the result of subduction processes at plate convergence areas (See Chap. 5).
The formation of volcanoes and the production of earthquakes along subduction
plate margins have a common origin. The loci of the major earthquakes are
clustered in the Benioff zone during the breaking up of a slab penetrating into the
Earth’s mantle below 50 km depth at a variable angle of about 20–50°. These deep
earthquakes often occur in the marginal basins at a distance (300–1000 km) from
the trenches. In the Indonesian region, the epicenters of deep earthquakes are often
located 500–600 km north of the Java trench. The strength is most intense in the
rigid lithosphere and vanishes slowly at depth within the mantle. In the immediate
vicinity of the Sumatra-Java (Indonesian) trench system, the greatest earthquakes
are shallow due to a low angle thrust during the breaking of the slabs (Kanamori
1971). The World’s most active earthquake regions are found in the Pacific convergence margins, which are rimed by deep trenches and arc volcanism.
During the Cenozoic period (\50 million years ago), the Pacific plate converged in the west at contact with the Asian Plate, and on the south at contact with
the Indian-Australia-New-Guinean plates that were moving northward. The areas
of Eastern Australia as well as New Guinea and Indonesia have all been affected
by such plate rearrangements. Earlier, during the late Paleozoic ([250 million
ago) and Triassic (200–250 Ma) periods, the granitic and volcanic terrain of the
Eastern Australia-New Guinea-Indonesian regions (including the Sumatra-Java
area) were separated from the Indian Ocean by a deep trench, with a depth of about
6000 m, bordering the islands of Java and Sumatra in Indonesia. Convergence of
the Pacific plate has created one of the World’s longest and deepest subducting
trenches. An example of this type of system of Pacific plate convergence and
subduction is seen on the Tonga-Kermadec volcanic arc and trench.
Tonga-Kermadec Volcanic Arc
The Tonga-Kermadec volcanic arc system is the locus of volcanic activity related
to the convergence of two plates: the Pacific and the Indo-Australian plates. The
Tonga-Kermadec system is 2,530 km long, making it one of the longest, continuous intra-oceanic arcs in the World. It exists in an area going from New Zealand
to the island of Samoa near latitude 15°S (de Ronde et al. 2005; Garry Massoth
2005 personal communication). This region is marked by an extensive felsic type
(rhyolite) of volcanism associated with considerable amounts of silica-enriched
products (Bloomer et al. 1994). The subducting plate is nearly perpendicular to the
350
10 Subduction Zones