10:45 AM - 11:00 AM
[SCG67-07] Metasomatic records of lithosphere prior to subduction inferred from petit-spot
Melt fractionations are required at the mid- or lower depth of lithosphere, given that bulk compositions clearly show fractionation trends of olivine in the absence of phenocrysts, in spite of raising lherzolitic xenoliths and xenocrystic olivines from deepest approximately 45 km (Yamamoto et al., 2015). Depth of the fractionation could be correspond to the σ3 rotation from extensionally lower to upper compressional lithosphere due to the concave flexure prior to outer rise (Valentine & Hirano, 2010). The high levels of carbon dioxide derived by petit-spot magma recently explains the low seismic velocity and high electrical conductivity of oceanic asthenosphere as the source mantle. Experimentally equilibrated petit-spot melt, adopted 10 wt % CO2 before emission (Okumura & Hirano, 2013), with harzburgite at the lower lithosphere implies the stagnation of ascending melt at the depth (Machida et al., 2017). Subducting lithosphere is likely metasomatized by the carbon-rich melt just prior to its subduction. The conventional theory about subducting lithosphere requires revision in light of recently obtained petit-spot data.