▪ Abstract The Re-Os isotope sytem, based on the long-lived β− transition of 187Re to 187Os, has matured to wide use in cosmochemistry and high-temperature geochemistry. The siderophilic/chalcophilic behavior of Re and Os is different from that of the elements that comprise most other long-lived radiogenic isotope systems. Magmatic iron meteorites (IIIAB, IIAB, IVA, and IVB) have Re-Os isochrons that indicate asteroidal core crystallization within the first 10–40 million years of Solar System evolution. Rocks from Earth's convecting mantle show generally chondritic Re/Os evolution throughout Earth history that is explained by the addition of highly siderophile elements to the mantle after core formation via late accretion. Oceanic basalts have Os-isotope systematics that improve the detailed geological interpretation of extant mantle components. Some portions of ancient subcontinental lithospheric mantle are severely depleted in Re and have correspondingly subchondritic 187Os/188Os, indicating long-term i...

THE Re-Os ISOTOPE SYSTEM IN COSMOCHEMISTRY AND HIGH-TEMPERATURE GEOCHEMISTRY

The Re-Os isotopic system in cosmochemistry and high temperature geochemistry

Here we describe a new chemical separation method for Os and an improved mass spectrometric procedure for Re and Os. This technique is based on the selective extraction of OsO4 from aqueous solution in liquid bromine. Among other advantages, this procedure avoids the cumbersome distillation procedure for Os and uses only commercial “off the shelf” PFA teflon labware. Blank levels for 0.5 g sample sizes are: 0.06 pg and 0.5 pg for Os and Re respectively. Samples containing as little as 1 pg g−1 Os can be analysed reliably with this method. Adaptation to other dissolution methods is also discussed.

Re‐Os Isotopic Measurements at the Femtomole Level in Natural Samples

The lanthanide tetrad effect and its correlation with k/rb, eu/eu*, sr/eu,y/ho, and zr/hf of evolving peraluminous granite suites

A review of the abundances and condensation temperatures of the elements and their nuclides in the solar nebula and in chondritic meteorites. Abundances of the elements in some neighboring stars are also discussed.

Abundances of the elements in the solar system

ReOs dating of molybdenites from ore deposits in Japan: Implication for the closure temperature of the ReOs system for molybdenite and the cooling history of molybdenum ore deposits

Inductively coupled plasma mass spectrometry employing isotope dilution quantification (ID-ICPMS) has been applied to determine trace levels of Ru, Pd, Ir, and Pt in geological materials. Accuracy, precision, and reproducibility are better than those obtained by other ICPMS calibration methods. For this purpose, it is important to achieve isotopic equilibrium by use of a microwave oven. Due to the trace concentration of these elements in geological samples, a method for separation of these elements from the matrix has been developed, taking advantage of formation of strong anionic complexes of Pd, Pt, Ru, and Ir in a hydrochloric acid medium. Since doubly charged complexes, MCl62-, are strongly sorbed by the anion exchange resin, whereas triply charged complexes, MCl63-, are weakly bound, various oxidizing agents were examined in this study to convert the lower oxidation states of these elements to their higher oxidation states. Systematic studies on retention and elution of these elements were carried ou...

Simultaneous Determination of Ruthenium, Palladium, Iridium, and Platinum at Ultratrace Levels by Isotope Dilution Inductively Coupled Plasma Mass Spectrometry in Geological Samples

Thermodynamic condition necessary for the appearance of negative Ce anomaly has been calculated with the simplest assumption that cerianite (CeO2) is a unique species of Ce(IV) in water system and that hardly soluble nature of CeO2 is the direct cause of the Ce anomaly. Only negative Ce anomalies possess straightforward information on the chemical conditions responsible for the anomalies. The extent of Ce anomaly has been calculated on the basis that the maximum dissolved concentration of Ce is limited by the maximum of activity of Ce3+ (aCe3+) allowed by the formation of cerianite, which is determined mainly by pH and EH. In the calculation the activities of Ce in any solid phases are assumed to be unity. The Ce anomaly line exhibiting a certain magnitude of negative anomaly was invented and drawn in the EH-pH diagram. We then applied the Ce anomaly line to some natural samples (seawater, ground water, iron formation, etc.) showing negative Ce anomalies and found that the Ce anomalies fairly well reflect the EH-pH condition of the aqueous phase. In applying the Cc anomaly line to natural systems, the key parameter is the activity of Ce∗3+, not the concentration of Ce∗ (hypothetical Ce without Ce(IV) states). Too much credence, however, should not be given to the simple calculation, owing to the complication of the natural system and the lack of appropriate thermodynamic data.

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Akimasa Masuda

Papers

ReOs dating of molybdenites from ore deposits in Japan: Implication for the closure temperature of the ReOs system for molybdenite and the cooling history of molybdenum ore deposits

Simultaneous Determination of Ruthenium, Palladium, Iridium, and Platinum at Ultratrace Levels by Isotope Dilution Inductively Coupled Plasma Mass Spectrometry in Geological Samples

A simple thermodynamic interpretation of Ce anomaly

The isotopic composition and atomic weight of molybdenum

Reliable Re-Os age for molybdenite