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In this study, we explored the impacts of radiation damage and chemical composition on the etching time of fission tracks in monazite. Despite the potential of monazite fission-track (MFT) dating as an ultralow-temperature thermochronology, the comprehensive effects of radiation damage and non-formula elements, especially on the etching rate of MFTs, remain unexplored, and established analytical procedures are lacking. We quantified the degree of radiation damage (ΔFHWM) in Cretaceous to Quaternary monazites distributed in the Japan arc through Raman spectroscopy and chemical composition analyses. Subsequently, MFT etching was performed to examine the correlation between these parameters and the etching time. Estimation of the degree of radiation damage showed an increase in radiation damage corresponding to the cooling age of each geological unit. For example, the Toya ignimbrite (ca. 0.1 Ma) and the Kurobegawa granodiorite (< 0.8 Ma), both of which are types of monazite from Quaternary geological units, have ΔFHWM values of 0.27 and 0.55 cm -1 , respectively. In contrast, the Muro ignimbrite (ca. 15 Ma) has a ΔFHWM value of 4.01 cm -1 , while the Kibe granite and the Sagawa granite, both of which are Cretaceous granitoids, yielded 7.35 and 6.31 cm -1 , respectively. MFT etching of these samples according to the existing recipe (6 M HCl at 90 °C for 60–90 min) was completed at 1200, 860, 210, 120, and 90 min for the Toya ignimbrite, Kurobegawa granodiorite, Muro ignimbrite, Sagawa granite, and Kibe granite, respectively. These outcomes highlight an inverse relationship between MFT etching time and the degree of radiation damage in monazite, while the correlation between MFT etching time and chemical composition was unclear. The results affirm earlier considerations that the etching rate of MFTs is strongly influenced by radiation damage. Conversely, young samples with lower levels of radiation damage exhibit higher chemical resistance, suggesting that existing etching recipes may not adequately etch MFTs. [ABSTRACT FROM AUTHOR]

The detection of gaseous elements (He, Ne, Kr, and Xe) and molecules (CO2, CH4, and NH3) using inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS) is described. In this study, sample gasses were introduced into a collision/reaction cell, and the sample gas components were ionised either by charge-transfer or by protonation reactions in the reaction cell through an ion reaction with the primary ions produced in the ICP. Ions originating from He and Ne, elements whose first ionisation potentials are greater than that of Ar, were not detected, whereas Kr and Xe were ionised through collision with Ar+. This implies that the ionisation can proceed basically by charge transfer reactions under equilibrium. The background counts for these elemental or molecular/polyatomic ions originating from either air engulfment into the ICP or from gas impurities in Ar can be effectively removed by the first quadrupole mass filter. The magnitude of softness/hardness of the ionisation can be controlled by selecting the primary ions (i.e., H+, Ar2+, and Ar+, in descending order of softness), and the resulting signal intensities for [M − H]+, M+, or [M + H]+ ions changed as reflecting a proton affinity or electronegativity of atoms, or polarity of molecules. Overall transmission efficiencies through ionisation, ion transport, mass separation, and ion detection processes for CO2+ and CH3+ were about 3.6 × 10−10%, 1.6 × 10−10%, and 3 × 10−8%, respectively. The technique described here can become a rapid and on-line analysis technique for both gaseous or volatile organic compounds (VOCs). [ABSTRACT FROM AUTHOR]

The opening of the Japan Sea led to the separation of southwest Japan from the Eurasian continent. Subsequent to this event, a diverse range of igneous activities occurred in southwest Japan. On the back‐arc side of the region, igneous activity commenced at approximately 22 Ma and persisted for an extended period. In the trench‐proximal region of southwest Japan, magmatism initiated around 15.6 Ma, immediately following the cessation of the Japan Sea opening, in correlation with the subduction of the Philippine Sea plate beneath southwest Japan. The Amakusa Islands in western Kyushu host felsic to intermediate igneous rocks with Miocene radiometric ages. There has been a debate regarding the attribution of the igneous rocks in Amakusa Island among the Miocene igneous rocks in southwest Japan. To address this issue, we conducted zircon U–Pb dating and analyzed the major‐ and trace‐element compositions of felsic igneous rocks in the Amakusa Islands to elucidate their characteristics. The obtained U–Pb ages range from 14.5 to 14.8 Ma, suggesting contemporaneity between magmatism in the Amakusa Islands and the Setouchi Volcanic Rocks in the trench‐proximal region of southwest Japan. The major and trace element compositions of the felsic igneous rocks exhibit similarities to the dacites of the Setouchi Volcanic Rocks. These findings support previous suggestions that the magmatism in the Amakusa Islands can be correlated with the Setouchi Volcanic Rocks, based on the discovery of a high‐Mg andesite dike and paleo‐stress analysis utilizing the direction of dikes and sills. Therefore, the Setouchi Volcanic Belt is proposed to extend further west than the previously identified Ohno volcanic rocks in eastern Kyushu. The subduction of the Shikoku Basin of the Philippine Sea plate toward western Kyushu supports the hypothesis that the Kyushu‐Palau Ridge was positioned west of Kyushu at ~15 Ma. [ABSTRACT FROM AUTHOR]