<scp>P</scp>otential <scp>M</scp>esozoic reference zircon from the <scp>U</scp>nazuki plutonic complex: geochronological and geochemical characterization

<jats:title>Abstract</jats:title><jats:p><jats:styled-content style="fixed-case">OT</jats:styled-content>4 zircon collected from <jats:styled-content style="fixed-case">O</jats:styled-content>to‐dani quartz diorite in <jats:styled-content style="fixed-case">U</jats:styled-content>nazuki, in the northeastern part of the <jats:styled-content style="fixed-case">H</jats:styled-content>ida <jats:styled-content style="fixed-case">B</jats:styled-content>elt, <jats:styled-content style="fixed-case">S</jats:styled-content>outhwest <jats:styled-content style="fixed-case">J</jats:styled-content>apan, was evaluated using microbeam analysis for its qualification as a <jats:styled-content style="fixed-case">M</jats:styled-content>esozoic reference zircon based on <jats:styled-content style="fixed-case">U</jats:styled-content>–<jats:styled-content style="fixed-case">P</jats:styled-content>b dating. The characterization of <jats:styled-content style="fixed-case">OT</jats:styled-content>4 zircon was carried out using a sensitive high‐resolution ion microprobe (<jats:styled-content style="fixed-case">SHRIMP</jats:styled-content> <jats:styled-content style="fixed-case">II</jats:styled-content>). Chemical zoning was revealed in some of the grains with a relatively high concentration of <jats:styled-content style="fixed-case">U</jats:styled-content> and <jats:styled-content style="fixed-case">T</jats:styled-content>h (up to 988 and 1054 ppm, respectively). The weighted mean <jats:styled-content style="fixed-case"><jats:sup>206</jats:sup>P</jats:styled-content>b/<jats:styled-content style="fixed-case"><jats:sup>238</jats:sup>U</jats:styled-content> age corrected by <jats:sup>207</jats:sup><jats:styled-content style="fixed-case">P</jats:styled-content>b was 191.1 ± 0.3 <jats:styled-content style="fixed-case">M</jats:styled-content>a (95% confidence limit) and was found to be almost constant for all the grains. The high crystallinity, the constant <jats:styled-content style="fixed-case">REE</jats:styled-content> abundance patterns, and the homogeneous <jats:styled-content style="fixed-case">H</jats:styled-content>f concentrations (8651 ± 466 ppm) indicate that the grains were not affected by any geological events after crystallization. Furthermore, the homogeneous <jats:styled-content style="fixed-case">H</jats:styled-content>f concentrations and consistency of the <jats:styled-content style="fixed-case">Ti</jats:styled-content>‐in‐zircon temperature (733 ± 34°<jats:styled-content style="fixed-case">C</jats:styled-content>) and the <jats:styled-content style="fixed-case">Z</jats:styled-content>r saturation temperature (728°<jats:styled-content style="fixed-case">C</jats:styled-content>) suggest that the <jats:styled-content style="fixed-case">OT</jats:styled-content>4 zircon crystallized over a short time. The <jats:styled-content style="fixed-case">OT</jats:styled-content>4 zircon contains enough radiogenic <jats:styled-content style="fixed-case"><jats:sup>206</jats:sup>P</jats:styled-content>b (>2 ppm) and <jats:styled-content style="fixed-case"><jats:sup>207</jats:sup>P</jats:styled-content>b (>0.1 ppm) to be detected by microbeam analysis, which indicates its potential of being an effective <jats:styled-content style="fixed-case">M</jats:styled-content>esozoic reference used in microbeam <jats:styled-content style="fixed-case">U</jats:styled-content>–<jats:styled-content style="fixed-case">P</jats:styled-content>b dating.</jats:p>