Abstract
The OIB(ocean-island basalt) source has been regarded to be a less-degassed reservoir compared to that of MORB(mid-ocean ridge basalt) based on noble gas istope signatures. However, apparent He contents in OIBs are not so abundant as expected from their noble gas signatures. Our studies have revealed that kimberlite magma sources are similar to those of OIBs and kimberlites contain abundant volatile elements including He. Furthermore,based on its eruption mode,it is conjectured that kimberlites would keep the chemical state of the source more directly compared to OIBs. Kimberlites suggests a possibility that the Earth's deep interior might be more reduced state than what has been considered so far.
