Generation of arc basalt magmas and thermal structure of the mantle wedge in subduction zones

摘要: The chemical compositions of primary magmas olivine tholeiite (OTB), high-alumina basalt (HAB), and alkali (AOB) are obtained by the maximum fractionation model for Quaternary magnesian basalts from Northeastern Japan arc. These assumed to have fractionated only crystals before eruption. melting phase relations three been determined under both anhydrous water-undersaturated conditions. AOB melt coexists with olivine, orthopyroxene, clinopyroxene at 17 kbar 1360°C conditions 23kbar 1320°C in presence 3wt % water. HAB also above phases 15 1340°C 1325°C 1.5 wt OTB melt, on other hand, orthopyroxene 11 water contents arc estimated be about 3, 1.5, nearly O AOB, HAB, OTB, respectively, basis solubility limit silicate melts. Based these estimates experimental results, suggested segregate mantle 23, 17, kbar, respectively. As temperatures segregation given appear too high a stable geotherm, diapir is most probable mechanism magma production subduction zone. Considering heat formation diapir, region higher than 1400°C has present wedge.