LGC-1 zircon reference material for in-situ (U-Th)/He dating

Sep 1, 2026

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A pairwise in-situ (U-Th)/He dating approach is presented to reduce matrix-related bias in U and Th measurements by using synthetic reference materials, contingent on finding a natural zircon reference with homogeneous (U-Th)/He age at ~10–100 µm. The newly characterized pale-yellow Sri Lanka gem LGC-1 satisfies this requirement: microscopy, cathodoluminescence, elemental mapping, and Raman show no zoning or heterogeneity. LA-ICP-MS provides 266 U, Th, and Pb measurements consistent within uncertainties; ID-ICP-MS and ID-TIMS validate Th/U ratio and concordia U/Pb ages, while in-situ (U-Th)/He analyses yield consistent 4He concentrations and ages. Shared zircon fractions support both in-situ and conventional calibration workflows.

LanguageEnglish

CategoryGeneral

FormatDOCX

Pages25

Reading Time9 min

AccessFree to download

Abstract

Introduction

Rationale for double-dating detrital zircons

In-situ U/Pb and in-situ (U-Th)/He methods

Pairwise dating requirements for age-reference materials

Existing zircon references and motivation for LGC-1

LGC-1: a zircon reference material for in-situ (U-Th)/He dating Yuntao Tian a,b, Pieter Vermeesch b, Martin Danišík c, Daniel J. Condon d, Wen Chen e, Barry, Kohn f, James Schwanethal b, Martin Rittner b a Guangdong Provincial Key Laboratory of Geodynamics and Geohazards, School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China b Department of Earth Sciences, University College London, London WC1E 6BT, UK c Auscope GeoHistory Facility, John de Laeter Centre, The Institute for Geoscience Research (TIGeR), Applied Geology/Applied Physics, Curtin University, Perth, WA, Australia d NERC Isotope Geosciences Laboratory, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK e Laboratory of Isotope Thermochronology, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China f School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia Corresponding author: Prof. Yuntao Tian School of Earth Sciences and Engineering Sun Yat-sen University Guangzhou, 510275 China Email: tianyuntao@mail.sysu.edu.cn Abstract A pairwise in-situ (U-Th)/He dating method has been proposed for mitigating matrix-related bias in U and Th measurements using synthetic reference materials. This method requires a natural zircon reference material whose (U-Th)/He age should be homogeneous on the scale (~10-100 µm) to be used in such dating experiments. A newly characterised zircon LGC-1 megacryst fulfils this requirement. This pale-yellowish, flawless Sri Lanka gem specimen is about 1.2*0.8*0.8 cm in size. Optical microscopy, cathodoluminescence-imaging, X-ray elemental mapping, and Raman spectroscopy on a large number of random shards did not reveal any detectable textural and compositional heterogeneity. Laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) analyses on a large number of randomly selected fragments yield 266 measurements of U, Th and Pb concentrations, which are within the corresponding experimental uncertainties. The weighted mean U, Th and Pb concentrations are 357.7 ± 1.8 ppm, 740.9 ± 5.0 ppm, and 39.06 ± 0.18 ppm, respectively, with a weighted mean Th/U ratio of 2.07 ± 0.01, indistinguishable from Isotope Dilution ICP-MS (ID-ICP-MS) and Thermal Ionization Mass Spectrometry (ID-TIMS) results. ID-TIMS U/Pb ages are concordant within uncertainties of decay constants, with a concordia age of 541.70 ± 0.70 Ma. Conventional (U-Th)/He dating on 28 random shards from the crystal in different laboratories gives a central age of 476.4 ± 5.7 Ma. Six in-situ (U-Th)/He analyses yield consistent 4He concentrations and ages with weighted mean values of 1248 ± 46 nmol/g and 462 ± 21 Ma, respectively. Fractions of this zircon have been shared with several laboratories in the Australia, China, UK and US, and are expected to serve as a reference for both in-situ and conventional (U-Th)/He analyses. The combination of analytical methods used to characterize LGC-1 zircon may be used as a template for future age reference calibration. Highlights: No texture and compositional zoning in zircon LGC-1 A zircon reference material for in-situ (U-Th)/He dating Suggestions for future age reference calibration Keywords: Zircon LGC-1, Reference material, In-situ (U-Th)/He dating, Geochronology. 1. Introduction Zircon is an extremely durable mineral, which is commonly found in siliciclastic rocks and is rich in U and Th. These properties make zircon uniquely well suited for sedimentary provenance studies. Using micro-analytical methods such as laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) or secondary ion mass spectrometry (SIMS), it has become routine practice to determine the probability distribution of ~100 detrital zircon U/Pb ages as a characteristic fingerprint to trace the flow of sand through modern and ancient sediment routing systems. Dozens of papers employing this method are published each year. The power of such provenance studies would g

FAQs

What problem does the pairwise in-situ (U-Th)/He method address?

It mitigates matrix-related bias in U and Th measurements by relying on a suitable reference material during age calculation.

What makes a zircon reference suitable for in-situ (U-Th)/He experiments?

Its (U-Th)/He age must be spatially homogeneous at the experimental scale (~10–100 µm), implying large, unzoned crystals with a simple thermal history.

How is LGC-1 zircon characterized to verify its homogeneity?

Optical microscopy, cathodoluminescence imaging, X-ray elemental mapping, and Raman spectroscopy on many random shards show no detectable textural or compositional heterogeneity, supported by concentration consistency from LA-ICP-MS measurements.

Sep 1, 2026

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