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Origin of magmas in subduction zones: a review of experimental studies.

Kushiro I - Proc. Jpn. Acad., Ser. B, Phys. Biol. Sci. (2007)

Bottom Line: Studies of the origin of magmas in subduction zones, particularly in the Japanese island arc, have been significantly advanced by petrological, geochemical, geophysical and experimental studies during last 50 years.Based on experimental studies, it is suggested that the compositions of primary magmas depend mainly on the H2O content and degree of melting in the melting zones, and that primary tholeiite magmas are formed by 10-25% melting of the source mantle containing less than 0.2 wt.% H2O.High-alumina basalt and alkali basalt magmas are formed by smaller degrees of melting of similar mantle, whereas primary boninite magmas are formed by more than 20% melting of the source mantle with more than 0.2 wt.% H2O, and finally, high-magnesia andesite magmas are formed by smaller degrees of melting of similar mantle.

View Article: PubMed Central - PubMed

ABSTRACT
Studies of the origin of magmas in subduction zones, particularly in the Japanese island arc, have been significantly advanced by petrological, geochemical, geophysical and experimental studies during last 50 years. Kuno's original model(1)) for magma generation in the Japanese island arc, that tholeiite magmas are formed at relatively shallow levels in the mantle on the Pacific Ocean side whereas alkali basalt magmas are formed in deeper levels on the Japan Sea side, stimulated subsequent studies, particularly high-pressure experimental studies in which the author participated. Recent seismic tomographic studies of regions beneath the Japanese island arc demonstrate that seismic low-velocity zones where primary magmas are formed have finger-like shapes and rise obliquely from the Japan Sea side toward the Pacific Ocean side. Based on experimental studies, it is suggested that the compositions of primary magmas depend mainly on the H2O content and degree of melting in the melting zones, and that primary tholeiite magmas are formed by 10-25% melting of the source mantle containing less than 0.2 wt.% H2O. High-alumina basalt and alkali basalt magmas are formed by smaller degrees of melting of similar mantle, whereas primary boninite magmas are formed by more than 20% melting of the source mantle with more than 0.2 wt.% H2O, and finally, high-magnesia andesite magmas are formed by smaller degrees of melting of similar mantle.

No MeSH data available.


Kuno’s model for the generation of tholeiite, high-alumina basalt and alkali olivine basalt magmas in the Japanese island arc.1), 10)
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f1-83_001: Kuno’s model for the generation of tholeiite, high-alumina basalt and alkali olivine basalt magmas in the Japanese island arc.1), 10)

Mentions: The origin of volcanic rocks and their primary magmas in subduction zones, including island arcs, is an important problem in igneous petrology. Studies of volcanic rocks in the Japanese island arc began in the late 19th century and greatly advanced during the early-middle 20th century, based mainly on the petrological characters of volcanic rocks.2)–8) Tomita5) recognized the occurrence of relatively silica-poor, alkali-rich rocks along the coast of the Japan Sea region and proposed the “Circum-Japan Sea alkaline province”. Later, Kuno1) clarified the lateral variations of volcanic rocks, particularly basalts, along the entire Japanese island arc. He found that relatively silica-rich, alkali-poor tholeiitic basalts (tholeiite) occur along the Pacific Ocean side (including the Izu islands), whereas those of relatively silica-poor alkali basalts occur on the Japan Sea side. These lateral variations of basalts were also observed in other parts of the circum-Pacific volcanic belt, including continental margins, such as along the western margins of both the north and south American continents. In these areas, tholeiitic basalts occur on the Pacific Ocean side and alkali basalts occur on the continental side. Furthermore, Kuno discussed the origin of such lateral variations based on his earlier work on the Hawaiian basalts8); tholeiitic basalt magmas are generated at relatively shallow levels in the mantle and alkali basalt magmas at deeper levels by partial melting of mantle peridotite. Kuno1) also took into account the seismic studies in the Japanese island arc. He realized that the boundary between the zones of tholeiitic basalt and alkali basalt nearly coincides with the 200 km depth contour of the deep seismic zone found by Wadati and Imai.9) Kuno1) proposed, based on this evidence, that tholeiitic basalt magmas are formed at depths shallower than about 200 km and alkali basalt magmas at depths greater than 200 km. Later, Kuno10) recognized the zone of high-alumina basalt between those of tholeiitic basalt and alkali basalt and suggested that high-alumina basalt magmas are generated at depths near 200 km (Fig. 1). Kuno’s studies greatly stimulated subsequent studies, particularly high-pressure experimental studies. In early 1960s the author was also stimulated by Kuno’s work and participated in the studies of magma genesis in island arcs by conducting high-pressure experiments. In this brief article, studies on the origin of subduction zone magmas are briefly reviewed, with special reference to the author’s relevant experimental studies. Possible physical conditions of magma generation in the mantle beneath the Japanese island arc are also discussed.


Origin of magmas in subduction zones: a review of experimental studies.

Kushiro I - Proc. Jpn. Acad., Ser. B, Phys. Biol. Sci. (2007)

Kuno’s model for the generation of tholeiite, high-alumina basalt and alkali olivine basalt magmas in the Japanese island arc.1), 10)
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3756732&req=5

f1-83_001: Kuno’s model for the generation of tholeiite, high-alumina basalt and alkali olivine basalt magmas in the Japanese island arc.1), 10)
Mentions: The origin of volcanic rocks and their primary magmas in subduction zones, including island arcs, is an important problem in igneous petrology. Studies of volcanic rocks in the Japanese island arc began in the late 19th century and greatly advanced during the early-middle 20th century, based mainly on the petrological characters of volcanic rocks.2)–8) Tomita5) recognized the occurrence of relatively silica-poor, alkali-rich rocks along the coast of the Japan Sea region and proposed the “Circum-Japan Sea alkaline province”. Later, Kuno1) clarified the lateral variations of volcanic rocks, particularly basalts, along the entire Japanese island arc. He found that relatively silica-rich, alkali-poor tholeiitic basalts (tholeiite) occur along the Pacific Ocean side (including the Izu islands), whereas those of relatively silica-poor alkali basalts occur on the Japan Sea side. These lateral variations of basalts were also observed in other parts of the circum-Pacific volcanic belt, including continental margins, such as along the western margins of both the north and south American continents. In these areas, tholeiitic basalts occur on the Pacific Ocean side and alkali basalts occur on the continental side. Furthermore, Kuno discussed the origin of such lateral variations based on his earlier work on the Hawaiian basalts8); tholeiitic basalt magmas are generated at relatively shallow levels in the mantle and alkali basalt magmas at deeper levels by partial melting of mantle peridotite. Kuno1) also took into account the seismic studies in the Japanese island arc. He realized that the boundary between the zones of tholeiitic basalt and alkali basalt nearly coincides with the 200 km depth contour of the deep seismic zone found by Wadati and Imai.9) Kuno1) proposed, based on this evidence, that tholeiitic basalt magmas are formed at depths shallower than about 200 km and alkali basalt magmas at depths greater than 200 km. Later, Kuno10) recognized the zone of high-alumina basalt between those of tholeiitic basalt and alkali basalt and suggested that high-alumina basalt magmas are generated at depths near 200 km (Fig. 1). Kuno’s studies greatly stimulated subsequent studies, particularly high-pressure experimental studies. In early 1960s the author was also stimulated by Kuno’s work and participated in the studies of magma genesis in island arcs by conducting high-pressure experiments. In this brief article, studies on the origin of subduction zone magmas are briefly reviewed, with special reference to the author’s relevant experimental studies. Possible physical conditions of magma generation in the mantle beneath the Japanese island arc are also discussed.

Bottom Line: Studies of the origin of magmas in subduction zones, particularly in the Japanese island arc, have been significantly advanced by petrological, geochemical, geophysical and experimental studies during last 50 years.Based on experimental studies, it is suggested that the compositions of primary magmas depend mainly on the H2O content and degree of melting in the melting zones, and that primary tholeiite magmas are formed by 10-25% melting of the source mantle containing less than 0.2 wt.% H2O.High-alumina basalt and alkali basalt magmas are formed by smaller degrees of melting of similar mantle, whereas primary boninite magmas are formed by more than 20% melting of the source mantle with more than 0.2 wt.% H2O, and finally, high-magnesia andesite magmas are formed by smaller degrees of melting of similar mantle.

View Article: PubMed Central - PubMed

ABSTRACT
Studies of the origin of magmas in subduction zones, particularly in the Japanese island arc, have been significantly advanced by petrological, geochemical, geophysical and experimental studies during last 50 years. Kuno's original model(1)) for magma generation in the Japanese island arc, that tholeiite magmas are formed at relatively shallow levels in the mantle on the Pacific Ocean side whereas alkali basalt magmas are formed in deeper levels on the Japan Sea side, stimulated subsequent studies, particularly high-pressure experimental studies in which the author participated. Recent seismic tomographic studies of regions beneath the Japanese island arc demonstrate that seismic low-velocity zones where primary magmas are formed have finger-like shapes and rise obliquely from the Japan Sea side toward the Pacific Ocean side. Based on experimental studies, it is suggested that the compositions of primary magmas depend mainly on the H2O content and degree of melting in the melting zones, and that primary tholeiite magmas are formed by 10-25% melting of the source mantle containing less than 0.2 wt.% H2O. High-alumina basalt and alkali basalt magmas are formed by smaller degrees of melting of similar mantle, whereas primary boninite magmas are formed by more than 20% melting of the source mantle with more than 0.2 wt.% H2O, and finally, high-magnesia andesite magmas are formed by smaller degrees of melting of similar mantle.

No MeSH data available.