5:15 PM - 6:30 PM
[SGL22-P04] Potential of multiple mineral age standard: preliminary study of the NST zircon from the Nisatai Formation in NE Japan
Keywords:zircon, U–Pb dating, hafnium isotopic composition, fission-track dating, standard material, NE Japan
Introduction
Recently, to reconstruct the history of upheaval and denudation, we can use multiple dating-method approaches with different isotopic systematics such as U–Pb and Fission-track (FT) double dating of single zircons by laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) and LA split stream (LASS) analysis to determine the U–Pb age and hafnium isotope compositions simultaneously. Therefore, it is also important to survey useful reference materials for multiple analytical methods (called multiple-mineral age standard materials). The Nisatai Formation, which occupies the basal part of Cenozoic strata in the Ichinohe district, NE Japan, consists mainly of conglomerate, sandstone, mudstone, and lapilli tuff (Tsujino et al., 2018). Some Nisatai Formation samples taken in the location called NST (NS-704B; Tagami et al., 1995) zircon U–Pb, zircon FT, and biotite K–Ar ages were reported by previous geochronological studies (Hasebe et al., 2013; Tagami et al., 1995; Sudo et al., 1996) and ranged 22–21 Ma (Table). We are checking the availability of the NST as a multi-mineral age standard material for various dating methods (e.g. Fukuda et al., 2021). In this study, to verify the availability we performed the U–Pb isotopic (partly FT) analysis of NST zircons among plural facilities. Additionally, we measured the Hf isotopic composition, which is used as a tracer to understand the time-integrated crustal evolution and mantle differentiation, of the NST. The results are summarized as follows.
Sample and Methods
The NST zircon samples were provided by Professor Tagami laboratory of Kyoto University. The samples were divided into the NST19, NST20a, and NST20b based on the year of collection and their lithofacies. The U–Pb isotopic analysis of the NST zircon were carried out in Tono Geoscience Center (JAEA), Geochemical Research Center (The University of Tokyo) and Graduate School of Environmental Studies (Nagoya University) by LA-ICPMS. Hf isotopic compositions of NST were measured in Tono Geoscience Center (JAEA) by LA-ICPMS.
Results and Discussion
U–Pb & FT dating: The weighted mean 206Pb/238U ages yielded ca. 23.0–21.3 Ma from each laboratories (Table) and the ages were consistent with the previous study (Hasebe et al., 2013). In some zircon grains, 206Pb/238U ages yielded ca. 30–26 Ma and FT analysis on 4Π geometry were older than those in previous studies (Tagami et al., 1995; Hasebe et al., 2013).
Hf isotopic composition: The 176Hf/177Hf ratio of 0.282824–0.282944 (weighted mean (2σ); 0.282895 +/- 29) were obtained from NST zircons. The Lu/Hf and Yb/Hf ratios of the NST zircon are higher than those of standard materials (e.g. 91500, MudTank) for hafnium isotope analysis. In hafnium isotope analysis, it is necessary to correct isobaric interferences to hafnium isotopes such as lutetium and ytterbium. Thus, the NST zircon may be an important secondary standard material to evaluate the accuracy of analysis.
References and Acknowledgements
Fukuda et al., 2021, Abst., Fission Track Research Group in Japan, 1. /Hasebe et al., 2013, Island Arc, 22, 281–290/Sudo et al., 1996, Mem., Fac., Sci., Kyoto Univ., 58, 21–40/Tagami et al., 1995, Geochemical J., 29, 207–210/Tsujino et al., 2018, Geology of the Ichinohe district, AIST, 161p.
M. Nagata, K. Kubomi and S. Otoh thank K. Yamamoto and Y. Asahara (Nagoya Univ.) for assistance U–Pb dating. This study was carried out under a contract with METI (Ministry of Economy, Trade and Industry) as part of its R&D supporting program for developing geological disposal technology.
Recently, to reconstruct the history of upheaval and denudation, we can use multiple dating-method approaches with different isotopic systematics such as U–Pb and Fission-track (FT) double dating of single zircons by laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) and LA split stream (LASS) analysis to determine the U–Pb age and hafnium isotope compositions simultaneously. Therefore, it is also important to survey useful reference materials for multiple analytical methods (called multiple-mineral age standard materials). The Nisatai Formation, which occupies the basal part of Cenozoic strata in the Ichinohe district, NE Japan, consists mainly of conglomerate, sandstone, mudstone, and lapilli tuff (Tsujino et al., 2018). Some Nisatai Formation samples taken in the location called NST (NS-704B; Tagami et al., 1995) zircon U–Pb, zircon FT, and biotite K–Ar ages were reported by previous geochronological studies (Hasebe et al., 2013; Tagami et al., 1995; Sudo et al., 1996) and ranged 22–21 Ma (Table). We are checking the availability of the NST as a multi-mineral age standard material for various dating methods (e.g. Fukuda et al., 2021). In this study, to verify the availability we performed the U–Pb isotopic (partly FT) analysis of NST zircons among plural facilities. Additionally, we measured the Hf isotopic composition, which is used as a tracer to understand the time-integrated crustal evolution and mantle differentiation, of the NST. The results are summarized as follows.
Sample and Methods
The NST zircon samples were provided by Professor Tagami laboratory of Kyoto University. The samples were divided into the NST19, NST20a, and NST20b based on the year of collection and their lithofacies. The U–Pb isotopic analysis of the NST zircon were carried out in Tono Geoscience Center (JAEA), Geochemical Research Center (The University of Tokyo) and Graduate School of Environmental Studies (Nagoya University) by LA-ICPMS. Hf isotopic compositions of NST were measured in Tono Geoscience Center (JAEA) by LA-ICPMS.
Results and Discussion
U–Pb & FT dating: The weighted mean 206Pb/238U ages yielded ca. 23.0–21.3 Ma from each laboratories (Table) and the ages were consistent with the previous study (Hasebe et al., 2013). In some zircon grains, 206Pb/238U ages yielded ca. 30–26 Ma and FT analysis on 4Π geometry were older than those in previous studies (Tagami et al., 1995; Hasebe et al., 2013).
Hf isotopic composition: The 176Hf/177Hf ratio of 0.282824–0.282944 (weighted mean (2σ); 0.282895 +/- 29) were obtained from NST zircons. The Lu/Hf and Yb/Hf ratios of the NST zircon are higher than those of standard materials (e.g. 91500, MudTank) for hafnium isotope analysis. In hafnium isotope analysis, it is necessary to correct isobaric interferences to hafnium isotopes such as lutetium and ytterbium. Thus, the NST zircon may be an important secondary standard material to evaluate the accuracy of analysis.
References and Acknowledgements
Fukuda et al., 2021, Abst., Fission Track Research Group in Japan, 1. /Hasebe et al., 2013, Island Arc, 22, 281–290/Sudo et al., 1996, Mem., Fac., Sci., Kyoto Univ., 58, 21–40/Tagami et al., 1995, Geochemical J., 29, 207–210/Tsujino et al., 2018, Geology of the Ichinohe district, AIST, 161p.
M. Nagata, K. Kubomi and S. Otoh thank K. Yamamoto and Y. Asahara (Nagoya Univ.) for assistance U–Pb dating. This study was carried out under a contract with METI (Ministry of Economy, Trade and Industry) as part of its R&D supporting program for developing geological disposal technology.