|Budget Amount *help
¥13,900,000 (Direct Cost : ¥13,900,000)
Fiscal Year 2000 : ¥1,700,000 (Direct Cost : ¥1,700,000)
Fiscal Year 1999 : ¥3,900,000 (Direct Cost : ¥3,900,000)
Fiscal Year 1998 : ¥8,300,000 (Direct Cost : ¥8,300,000)
Based on the discovery of intracrystalline isotope zonations in metamorphosed marbles a decade ago (Wada, 1988, Nature), we have predicted that such zonation will have far reaching implications on the behavior of metamorphic fluid movement in the Earth's crust right from the micron scale and ending up in a *rustal scale model. This methodology of isotope zonation studies was more refined by using secondary ion mass spectrometer (SIMS) and the results advanced our knowledge on isotope diffusion process in crystals (Graham et al., 1998, Wada a co-author). In this respect, further studies on the fluid flow on marbles with a new emphasis on zonation profiles in high temperature contact metamorphic aureoles were presented at the Goldschmidt conference 2000 at Oxford, UK (Wada, 2000).
During this year, we have succeeded in applying the carbon isotope geothermometry in ultrahigh temperature metamorphosed marbles from southern Indian granulite terrain. As shown in Satish-Kumar, M Wada, H and
others (2001), the temperature conditions were accurately determined for the region based on microscale isotope zonation profiles in calcite and graphite. The temperature conditions of such lower crustal granulites were as high as 1000℃, producing excellent matching with the petrologic mineral assemblages i ncluding the ultrahigh temperature index mineral of sapphirine. Thus the application of carbon isotope thermometry has provided a new tool in estimating accurately the ultrahigh-to high-temperature metamorphic conditions in the deep crust.
Another project of this financial support involves the establishing of a precise and detail laser based oxygen extraction system for silicate mineral phases. This utilizes a technique of decomposition of silicate bonds in minerals to separate oxygen using laser ablation in a bromine penta-fluoride atmosphere. The *onstruction of the system is completed and testing the vacuum conditions is underway. The predicted reproducibility of this system will not be as good as for carbonates, where we are now getting a less than 0.1‰ The important hurdles for this low accuracy lies in the oxygen preparation system and in the oxygen to CO2 conversion system. There is necessity for such accurate data in modeling the isotope diffusion profiles and the effect of fluids in such process. In order to achieve accuracy comparable to those we have for carbonates oxygen isotopes should be measured directly, after decomposition from silicate phases. We need a special mass spectrometer designed to measure oxygen isotopes directly from oxygen gas. This will also benefit in elucidating the multiple isotope (16O, 17O ＆ 18O) effect in natural sample Less