An ion microprobe provides advantages of in-situ isotopic measurements with high spatial resolution. It has been expected as a powerful analytical tool with a wide application of earth and planetary sciences. Sensitive High Resolution Ion MicroProbe (SHRIMP) developed at Australian National University has been successfully used to determine U-Th-Pb dating of a single grain zircon from Precambrian rocks. Although it is often recognized simply as a zircon analysis device, its capabilities should be applied to other geo- and cosmochemical studies. In this article we show the fundamental structure of SHRIMP, progress, recent studies and perspectives by using SHRIMP.

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This paper summarizes the fundamental concept of the stable isotope studies with emphasis on nitrogen isotope ratio based on unique characteristics of this parameter: interdiscirplinary nature, a chemical finger print of biogenic substances, and provinding a key to enter the new world of isotopomers. One primary goal of nitrogen isotope biogeochemical studies is elucidation of a general rule on the partition of the isotopes in molecules, biogenic materials, individuals and their cycling in biogeochemical systems. Current efforts on the general aspect of nitrogen isotope distribution are summarized.

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Incompatible elements are geochemically very important elements. For the determination of these elements, inductively coupled plasma mass spectrometry (ICP-MS) is very effective, because (1) multi-element analysis is available, (2) the sensitivity for the every incompatible element is high (<1 ng mL^-1), and (3) the interference spectra are very simple compared to the spectrometry, such as the inductively coupled plasma atomic emission spectrometry (ICP-AES) or the X-ray fluorescene analysis (XRF). A new analytical technique using ICP-MS was developed for the determination of the incompatible elements in rocks. The sensitivity of every incompatible element in rocks was 10 ng g^-1 level, and sufficient for the trace element geochemistry in most cases. This technique was applied to characterize the elemental behavior at the subduction zone, which is one of the most important place where material recycling between mantle and crust takes place. First, the elemental behavior during subduction-related high-pressure metamorphism was studied. In this study, not only rare-earth elements (REE) but also high field strength elements (HFSE) such as Zr, Nb, Hf or Ta were found to be mobile during metamorphism. This result indicates that more careful interpretation is required in the trace element geochemistry of metamorphic rocks, especially when we interpret a tectonic setting and magmatic evolution in the Archean. Second, in order to characterize slab-derived aqueous fluid, the analytical technique was combined with a high pressure-temperature experiment. In the experiment, a model slab material, metabasite was dehydrated under a high P-T condition, and the fluid was trapped in a model mantle material, dry olivine. The "squeezed" slab material was analyzed by ICP-MS, and it was found that LREE was depleted, while HREE remained constant. This suggests that the slab-derived fluid is LREE enriched, and the subducted slab has lower LREE/HREE ratio. Such interdisciplinary studies will be more and more important in the earth science in the forthcoming century. For this purpose, I am organizing "Comprehensive Elemental Analysis Project (CEAP)", which is briefly introduced in this paper.

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This paper describes advances in isotopic measurements that have been made with an inductively coupled plasma mass spectrometry (ICP-MS) and presents results of new experiments aimed at further progress of the isotope geochemistry. I begin with a direct measurement of in-situ Os isotopes in solid geochemical samples by laser microprobe-MC-ICPMS technique. In this study, possible isotopic variation in ¹⁸⁷Os/¹⁸⁸Os ratios have been measured with a laser pit size of 15μm. Although no significant isotopic variations could be detected from iridosmine samples, it was well demonstrated that the laser microprobe-MC-ICPMS has the potential to become a new analytical technique for the in-situ Re-Os age determinations of solid samples. I follow with a discussion of the Ge isotopes in metallic materials of meteorites. Although an abundance of data on Ge have been widely used for the classification of the iron meteorites, there still remains an enigma or a kind of gap between the simple theoretical model and the cosmochemical sequences of the iron meteorites drawn by the abundance of Ge data. In this study, I measured the Ge isotopic ratios of iron meteorites in order to discuss further the detailed formation mechanisms of the iron meteorites. The isotopic ratios for Ge were found to have small but significant variation mainly due to fractional evaporation. The data obtained here demonstrate clearly that Ge isotopes can provide us a useful information on the iron meteorite formation. This was followed by topics on zircon U-Pb chronology using a laser microprobe-ICPMS. Based on the data presented here, a realistic conclusion is that the laser microprobe-ICPMS technique has the strong potential as a reconnaissance analytical method and given increasing improvement in this instrument will in the future produce data comparable to ion probe techniques such as SHRIMP. Finally, I will report on the preliminary results of the new ion detector for ICP magnetic sector multiple collector mass spectrometer. The ion detector developed here enables us to detect several isotopic signals at the same time with an enhanced sensitivity compared with conventional Faraday collector. Principles of the new detector and its wide versatility will be described in this paper.

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It is shown that accurate rare-earth elements (REE) data in 22 geological rock reference samples (JB-1a, JB-2, JB-3, JA-1, JA-2, JA-3, JR-2, JR-2, JF-1, JG-1a, JG-2, JG-3, JGb-1. W-2, DNC-1, BIR-1, AGV-1, G-2, SDC-1, QLO-1, RGM-1 and STM-1) can be obtained by slight modification of the commonly used acid digestion procedure combined with ICP-AES analysis. The modified procedure consists of the decomposition of the samples with a sealed PFA vessel using acid mixture (HF+HClO₄+HNO₃+HCl) for 4 days on a 130℃ hot plate and the drying of the sample at 130℃ which is lower than commonly used temperatures, followed by dissolution with HCl and column separation of REEs. Our method minimizes the amount of undecomposed minerals and prevents the precipitation of fluorides and perchlorates during the digestion procedure. Twenty two geological standard samples of diverse matrices issued by Geological Survey of Japan (GSJ) and United States Geological Survey (USGS) were digested to assess the efficiency of the digestion procedure. Very small amount of undecomposed spinels and zircons were found in the digestion residues of JB-1a and JG-1a, respectively. The analytical results of REE for JB-1a and JG-1a agree well with the reported working values, indicating that the amount of undissolved minerals has practically small effect on REE data. Fluorides and perchlorates were found a fter the drying of the decomposed sample solutions at 180℃ for three samples (JG-1a, JG-2 and JR-2), on the other hand no precipitation is formed for all the samples digested when the drying was done at 130℃. The fluorides and perchlorates were shown to be responsible for the significant under-estimation of light REE concentrations in the samples. The REE data obtained by the drying at 130℃, however, showed good agreement (within 5% in most cases) with the working values. Thus, the formation of insoluble fluorides during the digestion procedure can be avoided by keeping the evaporation temperature at 130℃, without any additional agents. Our acid digestion method combined with ICP-AES yields accurate REE results, in good agreement with the working values for various standard rocks including granitic rocks.

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