Potential Mesozoic reference zircon from the Unazuki plutonic complex: geochronological and geochemical characterization

Abstract

OT4 zircon collected from Oto‐dani quartz diorite in Unazuki, in the northeastern part of the Hida Belt, Southwest Japan, was evaluated using microbeam analysis for its qualification as a Mesozoic reference zircon based on U–Pb dating. The characterization of OT4 zircon was carried out using a sensitive high‐resolution ion microprobe (SHRIMP II). Chemical zoning was revealed in some of the grains with a relatively high concentration of U and Th (up to 988 and 1054 ppm, respectively). The weighted mean 206Pb/238U age corrected by 207Pb was 191.1 ± 0.3 Ma (95% confidence limit) and was found to be almost constant for all the grains. The high crystallinity, the constant REE abundance patterns, and the homogeneous Hf concentrations (8651 ± 466 ppm) indicate that the grains were not affected by any geological events after crystallization. Furthermore, the homogeneous Hf concentrations and consistency of the Ti‐in‐zircon temperature (733 ± 34°C) and the Zr saturation temperature (728°C) suggest that the OT4 zircon crystallized over a short time. The OT4 zircon contains enough radiogenic 206Pb (>2 ppm) and 207Pb (>0.1 ppm) to be detected by microbeam analysis, which indicates its potential of being an effective Mesozoic reference used in microbeam U–Pb dating.

SHRIMP U–Pb age of SoriZ93 zircon from the Sori Granodiorite, Northeast Japan: a potential reference zircon of Late Cretaceous age

“…) and grains of a potential zircon standard OT4 of Jurassic age (Horie et al . ). The epoxy disc was ground and polished to reveal the cross‐section of the zircon grains.…”

U–Pb zircon geochronology of the Hida gneiss and granites in the Kamioka area, Hida Belt

“…An O 2 − primary ion beam of 1.5–2.5 nA was used to sputter an analytical spot with approximately 25 μm diameter. TEMORA2 zircon ( 206 Pb/ 238 U age = 416.8 ±1.3 Ma; Black et al, ), FC1 zircon ( 206 Pb/ 238 U age = 1 099.9 ±1.1 Ma; Paces & Miller, ), and OT4 ( 206 Pb/ 238 U age = 191.1 ±0.3 Ma; Horie, Takehara, Suda, & Hidaka, ) were used as reference materials for calibration of the 206 Pb/ 238 U ratio, and 91500 zircon (U concentration 81.2 ppm; Wiedenbeck et al, ) was used for calculation of the U concentration. The U–Pb data were reduced according to the procedure described by Williams (), using the SQUID2 Excel macro of Ludwig ().…”

LA-ICP-MS Zircon U—Pb Dating of Acidic Tuff from the Eocene Akasaki Formation, Amakusa, Kumamoto Prefecture, Western Kyushu, Japan: Implications for the Age of the Land Mammal Fauna in Japan

“…U-Pb dating of these samples was carried out by LA-ICP-MS using NWR213 (Electro Scientific Industries) and an Agilent 7700x (Agilent Technologies) at the National Museum of Nature and Science, Tsukuba, Ibaraki, Japan. We measured OT-4 (191.1±0.3 Ma;Horie et al, 2013) as a secondary standard and which yielded 192.7±3.4 Ma (n = 5, MSWD = 1.18). The experimental conditions and the procedures followed for the measurements were based on those of Tsutsumi et al (2012).…”