| Research Abstract |
We have performed the investigation on the recycling and evolution of crust and mantle materials based on noble gas isotope ratios and Ar-Ar dating in order to clarify the system and obtained the following results.
We found 3He/4He ratios of less than the atmospheric value in some mantle xenoliths from Sikhote Alin area, east Siberia. Based on the micro-Raman spectroscopic analysis of CO2 inclusions in olivine and pyroxene crystals, we have developed a method to evaluate the trapping pressure of CO2. By using the method, wee could estimate the trapping pressure for Sikhote Alin samples, which indicated the pressure of 0.96〜1.04Gpa, corresponding to the depth of about 30km. From such information, it is inferred that old subducted crustal materials might have affected the 3He/4He ratios and probably also affected the trace element compositions underneath the east Siberian continent. Furthermore, Ar-Ar dating for phlogopite in Horoman Peridotite Complex indicates an Ar-Ar age of about 21Ma with a signature of the occurrence of excess 40Ar. It suggests that the phlogopite might have formed secondarily at a depth where the atmospheric component affected to some extent through water. On the other hand, noble gas analysis for glassy samples which were collected by submersibles from the Loihi Volcano area suggests the effect of oceanic crustal materials. Noble gas analysis for samples from Reunion and Mauritius Islands indicate the lowering of 3He/4He ratios for samples of less than 1Ma from Mauritius Island compared to those of older samples from the island and those of Reunion Island. This seems to indicate the evolutional trend of a hotspot type oceanic island.
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