Characterization of PENG-16 Zircon as a Reference Material for U-Pb Geochronology by LA-ICP-MS

Uranium-Lead (U-Pb) geochronology is a reliable method for dating geological events and understanding crustal evolution. Zircon (ZrSiO₄) is widely used due to its high Pb closure temperature (>900 °C), capacity to incorporate U and Th, and resistance to alteration. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) has enhanced zircon dating by allowing in situ analyses with high spatial resolution. However, accuracy depends on the availability of isotopically homogeneous reference materials. With the depletion of standards like GJ-1, the development of new materials is necessary. PENG-16 zircon, distributed by the International Association of Geoanalysts (IAG) via the G-Chron program, is evaluated here for its suitability as a reference material in U-Pb geochronology. This work characterizes the textural, chemical and isotopic features of PENG-16 to assess its homogeneity and geochronological reliability. PENG-16 originated from ~400 kg of monzonite rock processed by IAG using mechanical and chemical separation techniques, yielding >99% zircon with grain sizes <200 µm. Grains were embedded in epoxy, polished, and analyzed using optical microscopy, Scanning Electron Microscopy (SEM) and Cathodoluminescence (CL) to investigate texture and zoning. LA-ICP-MS analyses were performed on 126 grains using a Thermo Finnigan Element II coupled to a 193 nm laser. Primary standards (BB and GJ-1) and a secondary standard (91500) were used for calibration and quality control. Raw data were processed using GLITTER, with normalization and corrections applied. Ages were calculated and plotted in Isoplot using Concordia diagrams. SEM and CL imaging showed that PENG-16 zircon has a well-preserved structure, minimal zoning, and few inclusions or fractures. U-Pb isotopic data revealed strong consistency in ²⁰⁷Pb/²⁰⁶Pb, ²⁰⁷Pb/²³⁵U and ²⁰⁶Pb/²³⁸U ratios. Concordant ages were 172 ± 13 Ma (GJ-1 normalized, MSWD = 0.32) and 165 ± 2 Ma (BB normalized, MSWD = 0.23), both within analytical uncertainty. Common Pb content was low (f206c < 0.04), reducing correction complexity. U concentrations ranged from 108 to 673 ppm, a suitable range for LA-ICP-MS without inducing Pb loss. Although some variation in U and Th was observed, age consistency was maintained, indicating closed-system behavior. PENG-16 zircon demonstrates isotopic and textural qualities suitable for use as a reference material in U-Pb geochronology by LA-ICP-MS. The preserved crystal structure, low common Pb content, and consistent ages across analyses support its potential application. Differences in age values using distinct standards likely reflect instrumental or calibration variations. The availability of several hundred grams of material and appropriate grain size for ablation reinforce its practical value. Further validation, including ID-TIMS analyses and interlaboratory comparison, is recommended to confirm its certification. Current results confirm its promise as a robust standard for the geochronological community.