Hideyuki Obayashi

In situ 207Pb/206Pb isotope ratio measurements using two Daly detectors equipped on an ICP-mass spectrometer

The simultaneous detection of 206Pb and 207Pb ions has been made by multiple-ion counting ICP-mass spectrometry using two Daly detectors (MC-ICPMS). To evaluate the long-term gain stability of the detectors, 135Ba/138Ba and 136Ba/138Ba ratios have been measured by a combination of Daly and Faraday detectors (135Ba(D)/138Ba(F)) and an electron multiplier and Faraday detectors (136Ba(EM)/138Ba(F)). The measured 136Ba(EM)/138Ba(F) ratio changed 2% through the 10-hour analysis, whereas the 135Ba(D)/138Ba(F) showed smaller changes (<0.5%) over the 10-hour period, demonstrating that the Daly detector could provide better gain stability against conventional electron multipliers. After the correction for the counting loss due to dead time, the Daly detector is capable of accepting signal intensities as high as 107 cps. This indicates that the overlap of the analysis range, between the Daly detector (100 to 107 cps) and the Faraday detector (104 to 1010 cps), would be at least two orders of magnitude, suggestive of easier cross calibration of the collector gain between the detectors. With the present two Daly detectors, in situ207Pb/206Pb ratio measurements have been made on the Nancy 91500 zircon standard through the sample introduction technique using laser ablation. The overall analytical precision and the relative deviation from the literature values were 5.1% and 0.04%, respectively. The data obtained here clearly demonstrate that the LA-MC-ICPMS technique equipped with the Daly detectors would become a major analytical tool for in situ U–Pb geochronology.

A long-forgotten ‘dinosaur’ bone from a museum cabinet, uncovered to be a Japan's iconic extinct mammal,Paleoparadoxia(Desmostylia, Mammalia)

Here, we report a new ‘discovery’ of a desmostylian fossil in the geological collection at a national university in Japan. This fossil was unearthed over 60 years ago and donated to the university. Owing to the original hand-written note kept with the fossil in combination with interview investigation, we were able to reach two equally possible fossil sites in the town of Tsuchiyu Onsen, Fukushima. Through the interviews, we learned that the fossil was discovered during construction of a debris flow barrier and that it was recognized as a ‘dinosaur’ bone among the locals and displayed in the Village Hall before/until the town experienced a fire disaster in 1954. As scientific findings, the fossil was identified to be a right femur of Paleoparadoxia (Desmostylia), which shows well-preserved muscle scars on the surface. The age was estimated to be 15.9 Ma or younger in zircon-dating. This study shows an excellent case that historical and scientific significances could be extracted from long-forgotten uncatalogued specimens as long as the original information is retained with the specimens.

iQuant2: Software for Rapid and Quantitative Imaging Using Laser Ablation-ICP Mass Spectrometry

We report on the development of a software program named iQuant2 which creates visual images from two-dimensional signal intensity data obtained by a laser ablation-ICP-mass spectrometry (LA-ICPMS) technique. Time-resolved signal intensity profiles can be converted to position resolved signal intensity data based on the rastering rate (μm s−1) of the laser ablation. Background signal intensities obtained without laser ablation (gas blank) are used as the background, and all of the blank-subtracted intensity data can be used for the imaging analysis. With this software, deformation of the created image can be corrected visually on a PC screen. The line profile analysis between the user-selected points can be observed using the iQuant2 software. To accomplish this, data points on the profile line were automatically calculated based on the interpolation between the analysis points. The resulting imaging data can be exported and stored as JPEG, BMP or PNG formats for further processing. Moreover, a semi-quantitative analysis can be made based on the coupling of the external correction of the RSF (relative sensitivity factor) using NIST SRM610 with normalization of the corrected signal intensity data being 100%. The calculated abundance data for major elements are in reasonable agreement with the values obtained by electron probe micro analyzer (EPMA). With the software developed in this study, both the rapid imaging and semi-quantitative determinations can be made.

U-Pb zircon geochronology of the North Pole Dome adamellite in the eastern Pilbara Craton

Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8551, Japan Department of Chemistry, Gakushuin University, Mejiro 1-5-1, Toshima-ku, Tokyo, 171-8588, Japan Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 606-8502, Japan WiscSIMS, Department of Geoscience, University of Wisconsin, 1215, W. Dayton Street, Madison, Wisconsin, 53706, USA Geochemistry Research Center, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033, Japan Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8551, Japan Correspondence Hisashi Asanuma, Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo, 152-8551, Japan. Email: asanuma.h.aa@m.titech.ac.jp Funding information Japan Society for the Promotion of Science, Grant/Award number: 16J07060; Ministry of Education, Culture, Sports, Science and Technology, Grant/Award numbers: 26106002, 26800259, 16J07060 Abstract Supracrustal rocks around the North Pole Dome area, Western Australia, provide valuable information regarding early records of the evolution of crustal processes, surface environments, and biosphere. Owing to the occurrence of the oldest known microfossils, the successions at the North Pole Dome area have attracted interest from many researchers. The Paleoarchean successions (Warrawoona Group) mainly comprise mafic-ultramafic greenstones with intercalated cherts and felsic lavas. Age constraints on the sediments have been mainly based on zircon U–Pb geochronology. However, many zircon grains have suffered from metamictization and contain anomalously high contents of common Pb, which makes interpretation of the U– Pb data complicated. In order to provide more convincing chronological constraints, an U–Pb Concordia age is widely accepted as the best estimate. Most zircons separated from two adamellites also suffered from severe metamictization. In our analyses, less metamictized domains were selected using a pre-ablation technique in conjunction with elemental mapping, and then their U–Pb isotopic compositions were determined with a laser ablation inductively coupled plasma mass spectrometry. Most analyzed domains contained certain amounts of common Pb (Pb/Pb > 0.000 1), whereas three and five U–Pb data points with less common Pb (Pb/Pb < 0.000 1) were obtained. These U–Pb datasets yielded U–Pb Concordia ages of ca 3 445 Ma and 3 454 Ma, respectively. These ages represent the timing of the adamellite intrusion, and constrain the minimum depositional age of the Warrawoona Group. In addition, a single xenocrystic zircon grain showed a Pb/Pb age of ca 3 545 Ma, supporting the idea that the sialic basement of the Pilbara Craton existed prior to 3 500 Ma. The in situ U–Pb zircon dating combined with the pre-ablation technique has the potentials to identify nonmetamictized parts and to yield precise and accurate geochronological data even from partially metamictized zircons.

Quantitative Analysis of Major and Minor Elements in Lead-free Solder Chip by LA-ICP-MS

A method was established for the quantitative analysis of the elements (Cu, Ag, Pb, and Sn) in solder samples by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), with Sn-based matrix matched standard solutions for defining the calibration curves. It was found that chloride-ion presented in commercially available Sn standard solution resulted in a precipitation of AgCl and caused the deterioration of the linearity of the calibration curve for Ag. Therefore, a laboratory-made chloride-free Sn solution was used to prepare Sn matrix matched standard solutions so as to ensure the stability of the elements including Ag. For the quantitative analysis of solder samples by LA-ICP-MS, the operating conditions of the LA instruments were set to obtain a fluence of over 12 J cm-2. This is mainly because of larger LA-induced elemental fractionations using a fluence of <10 J cm-2. The results for Ag, Cu, Pb, and Sn in a certified reference material (NMIJ CRM 8203-a) were close to, or in agreement with, the certified values, indicating that the present method was valid for the quantitative analysis of the elements in solder samples. In comparison to the certified values, relatively larger uncertainties were obtained for the analytical results by LA-ICP-MS, which could be attributed to the dependence on the homogeneity of the sample because the sample aliquots used for analysis were much smaller than those required for the traditional analytical procedures (i.e., sample quantity ratio of ca. 1:13000). Further improvement of the uncertainty might be obtained by using a larger sample quantity for the analysis by LA-ICP-MS so as to improve the representativeness of the sample.