Name : NAKAI,  Shun'ichi
            Position : Associate Professor
            Division/Center : Division of Geodynamics
            Research Area : Geochemistry

Research:

       My group is working on developing micro-analytical techniques for volcanic samples. Magma mixing, assimilation of crustal material
       and interaction with crustal fluid produce chemical and isotopic heterogeneity in a magma body, between phenocrysts or in some
       cases, within a phenocryst. Our main goal is to reconstruct the course of the chemical evolution of a magma, from magma formation,
       transfer, restoration in magma chamber, to eruption by developing analyticalmethods that enable us to decode geochemical records in
       volcanicproducts.

       To the goal, we are establishing analytical methods using an Inductively Coupled Plasma Mass Spectrometer (ICP-MS) combined
       with a laser abrasion system. So far we have succeeded in the spot analysis of trace elements such as REEs in clino-pyroxene,
       zircon. We are trying to improve analytical methods in order to apply this technique to plagioclase, common phenocrysts in island-arc
       volcanic rocks. This will enable us to obtain primary geochemical information of a magma before secondary processes such as crustal
       contamination.

       Another main research target is to set up uranium and thorium radioactivity disequilibrium method on young volcanic rocks. This
       technique will give us chronological constraints on processes involved in a volcanic eruption. We have established chemical methods
       of extraction, preconcentration and separation of U and Th from rock samples. We are working on isotopic analytical methods of Th
       using an IsoProbe (MicroMass), a sector type ICP-MS installed in Earthquake Research Institute.

       Beside the two main projects we are trying to develop isotopic analysis on various elements such as Li, Hf using the new ICP-MS to
       examine material transfer in island-arc environments.
 

Publications :

T. Yokoyama, S. Nakai, and H. Wakita, Helium and carbon isotopic compositions of hot spring gases in the Tibetan Plateau, Jour. Volcan. Geotherm. Res., 88, 99--107, 1999.

H. Sumino, S. Nakai, K. Nagao and K. Notsu, High 3He/4He ratio in xenoliths from Takashima: evidence for plume type volcanism in southwestern Japan, Geophys. Res. Lett., 27, 8, 1211--1214, 2000.