2:15 PM - 2:30 PM
[SCG57-09] Assessment of the applicability of U–Th dating to Hematite
Keywords:Hematite, U-Th dating, LA-ICP-MS, Quaternary geochronology
U-Th dating of zircon and ilmenite has been recently developed to constrain the chronology of Quaternary volcanic activity [1, 2]. While these methods are effective in determining the timing of its crystallization at high temperatures, they are less suitable for elucidating the duration of hydrothermal processes, which occur at lower temperatures. A comprehensive understanding of volcanic activity requires integrating both high- and low-temperature processes. Therefore, this study examines the applicability of U-Th dating to hematite (Fe2O3) to provide a more detailed assessment of hydrothermal system evolution. Hematite contains U at concentrations of several ppm and has a low initial Pb content, making it a suitable mineral for U-Pb geochronology [3, 4]. Recent advancements in in-situ analytical techniques, particularly laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), have facilitated extensive U-Pb dating of hematite in banded iron formations and ore deposits [5, 6]. Additionally, it is widely found in hydrothermal alteration zones, banded iron formations, and volcanic rocks, often preserving growth textures. The application of U-Th dating to hematite may offer new insights into the duration of hydrothermal activity and the temporal evolution of mineral growth.
In this study, we analyzed two hematite samples-one from Gibo-Fujisen, Shimotokuyama, Okayama Prefecture, and the Ohachi crater of Kirishima volcano, Kagoshima Prefecture. Using LA-ICP-MS, we measured the concentrations and spatial distributions of U, Th, and Pb to assess the feasibility of U-Th dating.
Preliminary results indicate that U concentrations in hematite range from 0.12 to 0.35 ppm, while both Pb and Th concentrations remain low, below 0.01 ppm. These findings suggest that hematite formed during volcanic activity is amenable not only to U-Pb dating but also to U-Th dating. However, under the current analytical conditions, the detection of 230Th requires a large sampling spot of 500 um square, with each measurement requiring ~125 seconds of signal acquisition time. Consequently, improving analytical sensitivity at smaller spatial scales remains a key challenge. The results of this study contribute to the temporal evolution of hydrothermal alteration. Future applications may include refining constraints on late-stage alteration processes in volcanic systems and expanding the applicability of U-Th dating under oxidative conditions.
References: [1] Niki S. et al. Geostand. Geoanal. Res. 46, 589-602 (2022). [2] Keller F. et al. Geostand. Geoanal. Res. 46, 465-475 (2022). [3] Duff M. C. et al. Geochim. Cosmochim. Acta 66, 3533-3547 (2002). [4] Courtney-Davies L. et al. Geostand. Geoanal. Res. 45, 143-159 (2021). [5] Ciobanu C. L. et al. Precambrian Res. 238, 129-147 (2013). [6] Courtney-Davies L. et al. Chem. Geol. 513, 54-72 (2019).
In this study, we analyzed two hematite samples-one from Gibo-Fujisen, Shimotokuyama, Okayama Prefecture, and the Ohachi crater of Kirishima volcano, Kagoshima Prefecture. Using LA-ICP-MS, we measured the concentrations and spatial distributions of U, Th, and Pb to assess the feasibility of U-Th dating.
Preliminary results indicate that U concentrations in hematite range from 0.12 to 0.35 ppm, while both Pb and Th concentrations remain low, below 0.01 ppm. These findings suggest that hematite formed during volcanic activity is amenable not only to U-Pb dating but also to U-Th dating. However, under the current analytical conditions, the detection of 230Th requires a large sampling spot of 500 um square, with each measurement requiring ~125 seconds of signal acquisition time. Consequently, improving analytical sensitivity at smaller spatial scales remains a key challenge. The results of this study contribute to the temporal evolution of hydrothermal alteration. Future applications may include refining constraints on late-stage alteration processes in volcanic systems and expanding the applicability of U-Th dating under oxidative conditions.
References: [1] Niki S. et al. Geostand. Geoanal. Res. 46, 589-602 (2022). [2] Keller F. et al. Geostand. Geoanal. Res. 46, 465-475 (2022). [3] Duff M. C. et al. Geochim. Cosmochim. Acta 66, 3533-3547 (2002). [4] Courtney-Davies L. et al. Geostand. Geoanal. Res. 45, 143-159 (2021). [5] Ciobanu C. L. et al. Precambrian Res. 238, 129-147 (2013). [6] Courtney-Davies L. et al. Chem. Geol. 513, 54-72 (2019).