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Volcanic arc above subduction zone is a manifestation of magma generation below the Earth’s surface. Magma generation in subduction zone focuses on the potential sources of partial melting, mechanism of partial melting, and types of magma generated. Magma generated in subduction zone will ascent to the surface as a consequence of buoyancy. Assimilation and fractional crystallization (AFC) will take place, especially in active continental margin.

Volcanic arc above subduction zone is a manifestation of magma generation below the Earth’s surface. Magma generation in subduction zone focuses on the potential sources of partial melting, mechanism of partial melting, and types of magma generated. Magma generated in subduction zone will ascent to the surface as a consequence of buoyancy. Assimilation and fractional crystallization (AFC) will take place, especially in active continental margin.

Potential sources of magma generation are the subducted oceanic crust, [[mantle]] wedge, and sea water. Oceanic crust, as previously discussed, consists of terrigenous, carbonate and pelagic sediments, and also sedimentary rock, basalt, and gabbro. Mantle wedge as a part of asthenosphere provides lherzolite and harzburgite. Sea water doesn’t provide silicate materials in magma generation. Otherwise, sea water takes a role in reducing solidus of silicate material. As a result, partial melting can be achieved at lower temperature. Water may reduce the temperature of partial melting about 300oC. Wilson<ref name=Wilson>Wilson, Majorie. 2007. Igneous Petrogenesis: A Global Tectonic Approach. Dordrecht: Springer.</ref> proposed specific potential sources of partial melting:

Potential sources of magma generation are the subducted oceanic crust, [[mantle]] wedge, and sea water. Oceanic crust, as previously discussed, consists of terrigenous, carbonate and pelagic sediments, and also sedimentary rock, basalt, and gabbro. Mantle wedge as a part of asthenosphere provides lherzolite and harzburgite. Sea water doesn’t provide silicate materials in magma generation. Otherwise, sea water takes a role in reducing solidus of silicate material. As a result, partial melting can be achieved at lower temperature. Water may reduce the temperature of partial melting about 300oC. Wilson<ref name=Wilson>Wilson, M., 2007, Igneous Petrogenesis: A Global Tectonic Approach. Dordrecht: Springer.</ref> proposed specific potential sources of partial melting:

* Amphibolite, with or without aqueous fluid

* Amphibolite, with or without aqueous fluid

* Eclogite, with or without aqueous fluid

* Eclogite, with or without aqueous fluid

Magma generation of subduction zone greatly involves dehydration process. Prograde metamorphism occurs as the plate subducting. Increasing pressure and temperature dehydrate OH-bearing minerals, such as hornblende and biotite. Zeolite may prograde to amphibolite facies, then to eclogite facies. Water produced from metamorphism may occur at depth of 80 – 125 km. As water generated, it migrates upward as intergranular fluid. Water supply from subducted slab lowers the solidus of the mantle wedge.

Magma generation of subduction zone greatly involves dehydration process. Prograde metamorphism occurs as the plate subducting. Increasing pressure and temperature dehydrate OH-bearing minerals, such as hornblende and biotite. Zeolite may prograde to amphibolite facies, then to eclogite facies. Water produced from metamorphism may occur at depth of 80 – 125 km. As water generated, it migrates upward as intergranular fluid. Water supply from subducted slab lowers the solidus of the mantle wedge.

Magma generated from mantle wedge in dry condition is basaltic or picritic in composition.<ref name=Wilson /> The presence of volatiles (H2O and CO2) can produce magma with higher silica content. Andesite can be directly produced from mantle wedge at depth less than 40 km with concentration of H2O of 15 wt. % (Mysen, 1982 and Wyllie, 1982 in Wilson<ref name=Wilson />).

Magma generated from mantle wedge in dry condition is basaltic or picritic in composition.<ref name=Wilson /> The presence of volatiles (H2O and CO2) can produce magma with higher silica content. Andesite can be directly produced from mantle wedge at depth less than 40 km with concentration of H2O of 15 wt. % (<ref>Mysen, B.O., 1982, The role of mantle anatexis, in R. S. Thorpe (ed.), Andesites: orogenic andesites and related rocks, Chichester: Wiley, pp. 489–522.</ref><ref>Wyllie, P. J., 1982, Subduction products according to experimental prediction: Geological Society of America Bulletin, vol. 93, pp. 468-476.</ref>>).

Boron, beryllium, thorium, and lead are possible indicators in determining the mode of flow within mantle wedge. Boron indicates transportation by fluid, while thorium and beryllium are effectively transported by melts.

Boron, beryllium, thorium, and lead are possible indicators in determining the mode of flow within mantle wedge. Boron indicates transportation by fluid, while thorium and beryllium are effectively transported by melts.