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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.


Relationships between elastic wave velocities and melt fraction (degree of melting) of mantle peridotite (spinel-lherzolite) at 1.0 and 0.5 GPa.56)–58) a: Vp; b: Vp and Vs relative to those at the solidus temperature (Vp/Vpm and Vs/Vsm, respectively). Both of them are nearly identical.
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f11-83_001: Relationships between elastic wave velocities and melt fraction (degree of melting) of mantle peridotite (spinel-lherzolite) at 1.0 and 0.5 GPa.56)–58) a: Vp; b: Vp and Vs relative to those at the solidus temperature (Vp/Vpm and Vs/Vsm, respectively). Both of them are nearly identical.

Mentions: Recently, significant progress has been made in understanding the physical properties of the mantle wedge beneath the Japanese island arc based on 3-dimensional seismic tomography. Fig. 10 reproduces P-wave velocity perturbations in northeast Honshu as determined by Nakajima et al.,55) who made seismic wave observations at 230 stations. As shown in the figure, the low-velocity region for P waves extends from deeper levels on the Japan Sea side to shallower levels on the Pacific Ocean side where many active volcanoes exist. The negative perturbation in most parts of the low velocity regions beneath northeast Honshu ranges from 3 to 6%. The S-wave velocities are also small in these regions. Velocities of P and S waves generally decrease with increasing temperature. In particular, S-wave velocities drastically decrease as melting begins to occur. It is most likely, therefore, that the low-velocity regions beneath northeast Honshu are relatively high in temperature and partial melting likely occurs in these regions. The velocities of both P and S waves decrease with increasing degree of melting or the amount of melt generated. The relationship between elastic wave velocities and the degree of melting (melt fraction) has been determined at 1 and 0.5 GPa for a mantle peridotite.56), 57)Fig. 11a shows P-wave velocity changes as function of melt fraction at 1.0 GPa, and Fig. 11b shows P-and S-wave velocity changes relative to those at the solidus temperature as function of melt fraction.58) The 3–6% negative perturbation corresponds to 2–5 vol.(volume)% melt fraction from the relationship in Fig. 11a, and to 2–6 vol.% from Fig. 11b (including uncertainties of the measurements of approximately ±1 absolute % in the 3–5% range). Under anhydrous conditions, 2–6 vol.% (2–5 wt.%) melts are formed at 1320–1360 °C at 1.5 GPa by partial melting of a depleted peridotite (MORB source peridotite) using the calculations of Gaetani and Grove.41) In the presence of H2O, temperature for producing the same amount of melt lowers significantly as mentioned before; for example, in the presence of 0.15 wt.% H2O, 2–5 wt.% melts are formed from the same depleted peridotite at 1190–1300 °C at 1.5 GPa. The amount of H2O present in the mantle beneath the Japanese island arc and other subduction zones is not known. However, based on the H2O contents in melt inclusions in olivine in primitive island arc magmas and the extents of melting estimated above (Fig. 9), the H2O contents in the source mantle would range from 0.1–0.2 wt.% for tholeiite and high-alumina basalt (and probably some alkali basalt) magmas, and 0.2–0.5 wt.% for boninite and high-magnesia andesite magmas. The temperatures calculated using the calculations of Gaetani and Grove with 0.15 wt.% H2O would be reasonable estimates for Japanese island arc and many other subduction zones, except for the areas where boninite and high-magnesian andesites dominate.


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

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

Relationships between elastic wave velocities and melt fraction (degree of melting) of mantle peridotite (spinel-lherzolite) at 1.0 and 0.5 GPa.56)–58) a: Vp; b: Vp and Vs relative to those at the solidus temperature (Vp/Vpm and Vs/Vsm, respectively). Both of them are nearly identical.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f11-83_001: Relationships between elastic wave velocities and melt fraction (degree of melting) of mantle peridotite (spinel-lherzolite) at 1.0 and 0.5 GPa.56)–58) a: Vp; b: Vp and Vs relative to those at the solidus temperature (Vp/Vpm and Vs/Vsm, respectively). Both of them are nearly identical.
Mentions: Recently, significant progress has been made in understanding the physical properties of the mantle wedge beneath the Japanese island arc based on 3-dimensional seismic tomography. Fig. 10 reproduces P-wave velocity perturbations in northeast Honshu as determined by Nakajima et al.,55) who made seismic wave observations at 230 stations. As shown in the figure, the low-velocity region for P waves extends from deeper levels on the Japan Sea side to shallower levels on the Pacific Ocean side where many active volcanoes exist. The negative perturbation in most parts of the low velocity regions beneath northeast Honshu ranges from 3 to 6%. The S-wave velocities are also small in these regions. Velocities of P and S waves generally decrease with increasing temperature. In particular, S-wave velocities drastically decrease as melting begins to occur. It is most likely, therefore, that the low-velocity regions beneath northeast Honshu are relatively high in temperature and partial melting likely occurs in these regions. The velocities of both P and S waves decrease with increasing degree of melting or the amount of melt generated. The relationship between elastic wave velocities and the degree of melting (melt fraction) has been determined at 1 and 0.5 GPa for a mantle peridotite.56), 57)Fig. 11a shows P-wave velocity changes as function of melt fraction at 1.0 GPa, and Fig. 11b shows P-and S-wave velocity changes relative to those at the solidus temperature as function of melt fraction.58) The 3–6% negative perturbation corresponds to 2–5 vol.(volume)% melt fraction from the relationship in Fig. 11a, and to 2–6 vol.% from Fig. 11b (including uncertainties of the measurements of approximately ±1 absolute % in the 3–5% range). Under anhydrous conditions, 2–6 vol.% (2–5 wt.%) melts are formed at 1320–1360 °C at 1.5 GPa by partial melting of a depleted peridotite (MORB source peridotite) using the calculations of Gaetani and Grove.41) In the presence of H2O, temperature for producing the same amount of melt lowers significantly as mentioned before; for example, in the presence of 0.15 wt.% H2O, 2–5 wt.% melts are formed from the same depleted peridotite at 1190–1300 °C at 1.5 GPa. The amount of H2O present in the mantle beneath the Japanese island arc and other subduction zones is not known. However, based on the H2O contents in melt inclusions in olivine in primitive island arc magmas and the extents of melting estimated above (Fig. 9), the H2O contents in the source mantle would range from 0.1–0.2 wt.% for tholeiite and high-alumina basalt (and probably some alkali basalt) magmas, and 0.2–0.5 wt.% for boninite and high-magnesia andesite magmas. The temperatures calculated using the calculations of Gaetani and Grove with 0.15 wt.% H2O would be reasonable estimates for Japanese island arc and many other subduction zones, except for the areas where boninite and high-magnesian andesites dominate.

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.