Changes

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. % (<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>>).

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.