Kentaro Hattori

U–Pb age determination for zircons using laser ablation-ICP-mass spectrometry equipped with six multiple-ion counting detectors

Precise zircon U–Pb age determinations have been made on Plesovice zircon using laser ablation-multiple ion counting-inductively coupled plasma-mass spectrometry (LA-MIC-ICP-MS). To achieve high precision and high spatial resolution age determination, multiple ion counting using six electron multipliers was employed. The intensities of Hg–Pb–U isotope (202Hg, 204(Hg + Pb), 206Pb, 207Pb, 208Pb, and 238U) signals were monitored simultaneously without mass scanning. In static acquisition mode, the resultant 238U–206Pb concordia age for Plesovice was 336.3 ± 1.9 Ma, demonstrating improved precision over that achieved using a magnetic sector-based single-collector-ICP-MS, which was 340.3 ± 3.5 Ma for Plesovice. A high duty cycle can be achieved, along with a short integration time or a small sample volume for analysis, allowing high spatial resolution. More importantly, downhole fractionation can be reduced with a shallow ablation pit. To take full advantage of the setup, a one-second LA analysis (8 laser shots with an 8 Hz repetition rate) was adopted for U–Pb age determination. The resultant concordia age for Plesovice was 339.5 ± 6.7 Ma, demonstrating that the repeatability and laboratory bias precision of the resultant age data were comparable to conventional ablation with a single-collector-ICP-MS. The depths and crater diameters of the ablation pits were, respectively, about >1 μm and 25 μm. The data presented herein demonstrate clearly that multiple ion counting-ICP-MS can become a fast and user-friendly tool for use in U–Pb zircon geochronology.

Long-lasting Extreme Magnetic Storm Activities in 1770 Found in Historical Documents

Dim red aurora at low magnetic latitudes is a visual and recognized manifestation of geomagnetic storms. The great low-latitude auroral displays seen throughout East Asia on 16-18 September 1770 are considered to manifest one of the greatest storms. Recently found 111 historical documents in East Asia attest that these low-latitude auroral displays were succeeding for almost 9 nights during 10-19 September 1770 in the lowest magnetic latitude areas (< 30{\deg}). This suggests that the duration of the great magnetic storm is much longer than usual. Sunspot drawings from 1770 reveals the fact that sunspots area was twice as large as those observed in another great storm of 1859, which substantiates this unusual storm activities in 1770. These spots likely ejected several huge, sequential magnetic structures in short duration into interplanetary space, resulting in spectacular world-wide aurorae in mid-September 1770. These findings provide new insights about the history, duration, and effects of extreme magnetic storms that may be valuable for those who need to mitigate against extreme events.

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 great space weather event in February 1730

Aims. Historical records provide evidence of extreme magnetic storms with equatorward auroral extensions before the epoch of systematic magnetic observations. One significant magnetic storm occurred on February 15, 1730. We scale this magnetic storm with auroral extension and contextualise it based on contemporary solar activity. Methods. We examined historical records in East Asia and computed the magnetic latitude (MLAT) of observational sites to scale magnetic storms. We also compared them with auroral records in Southern Europe. We examined contemporary sunspot observations to reconstruct detailed solar activity between 1729 and 1731. Results. We show 29 auroral records in East Asian historical documents and 37 sunspot observations. Conclusions. These records show that the auroral displays were visible at least down to 25.8{\deg} MLAT throughout East Asia. In comparison with contemporary European records, we show that the boundary of the auroral display closest to the equator surpassed 45.1{\deg} MLAT and possibly came down to 31.5{\deg} MLAT in its maximum phase, with considerable brightness. Contemporary sunspot records show an active phase in the first half of 1730 during the declining phase of the solar cycle. This magnetic storm was at least as intense as the magnetic storm in 1989, but less intense than the Carrington event.

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.

Monazite Behaviour and Time-scale of Metamorphic Processes along a Low-pressure/High-temperature Field Gradient (Ryoke Belt, SW Japan)

Low-pressure/high-temperature metamorphic rocks exposed in the western part of the Ryoke belt (Iwakuni–Yanai area, SW Japan) include a section with increasing temperature conditions from 425 to 880 C. We use this setting to explore the evolution of monazite grain size, texture and composition, and variations in the whole-rock composition of 11 metapelite, metapsammite or metachert samples collected along the metamorphic field gradient. Monazite grain size increases with rising metamorphic grade, regardless of the whole-rock composition. From lowto high-grade conditions we infer: (1) the initial nucleation of monazite aggregates after allanite ( 425 C); (2) monazite coarsening and coalescence driven by incipient monazite recycling; that is, dissolution of small grains to grow larger ones by Ostwald ripening (500–600 C); (3) a first major recycling stage enhanced by fluid liberation owing to muscovite breakdown (600–630 C); (4) a second recycling stage assisted by an increase in the proportion of anatectic melt owing to biotite breakdown (> 850 C). A succession of four compositional domains is recognized in monazite. We emphasize the usefulness of comparing their Ce/ThMnz, Ce/YMnz and Th/UMnz molar ratios with those derived from whole-rock analyses to constrain the origin of each domain. Domain I, with variable ratios, reflects the progressive transfer of Th 6 U from allanite to monazite at low-grade conditions. Domain II, with Ce/ThMnz matching the whole-rock values, indicates growth under rock(decimetre)scale equilibrium conditions. Domains II and III, with Th/UMnz and Ce/YMnz departing from the whole-rock values, record the competition with zircon (for U) and garnet (for Y) during growth at peak P–T conditions. Domain IV points to Y supply by garnet resorption during retrograde chloritization (< 550 C). In the highest-grade sample, zircon grains included in garnet or cordierite show metamorphic rims with sillimanite and Si-rich inclusions. These rims formed at suprasolidus conditions (650–880 C) and yield Pb/U ages of 103–97 Ma (6 5 Ma), which bracket the timing of high-temperature metamorphism. Monazite dating by electron microprobe and laser ablation inductively coupled plasma mass spectrometry reveals two age groups. For domains I–III, some relatively old Pb/U ages (99–95 6 3–5 Ma) represent minimum estimates for the timing of prograde to peak metamorphism, whereas the similar oldest Pb/U age for domain IV VC The Author(s) 2018. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com 1109 J O U R N A L O F P E T R O L O G Y Journal of Petrology, 2018, Vol. 59, No. 6, 1109–1144 doi: 10.1093/petrology/egy056 Advance Access Publication Date: 11 June 2018

Quantitative Elemental Bioimaging Protocol Using Femtosecond-Laser Ablation-ICP-Mass Spectrometry Coupled with Glass Standard Reference Material

We have developed new analytical technique for the quantitative elemental imaging for trace elements using a femtosecond-laser ablation-ICP-mass spectrometry (fs-LA-ICP-MS). With the laser ablation under the finely controlled fluence, sliced alveolar tissue samples (thickness 1 μm), placed on the glass slide, were totally ablated, and the laser-induced sample aerosols were introduced into the ICP. Hence, no laser ablation was achieved on the glass substrate because the laser fluence was lower than the energy threshold for the laser ablation phenomena of glass materials. Under the total ablation conditions, the ablated volume of the sample could be well defined, and therefore, concentrations of the analytes can be calibrated based on the signal intensity data and the volume of the sample and glass standard reference material. Combination of the LA-ICP-MS technique and the preferential and total ablation achieved by the soft ablation protocol can become a powerful method for studying the trace elements and pharmacokinetics containing metal elements through the quantitative imaging. Analytical spatial resolution of the imaging analysis as well as the detection limit of the present analytical technique will be discussed in this study.