A New Appraisal of Sri Lankan BB Zircon as a Reference Material for LA‐ICP‐MS U‐Pb Geochronology and Lu‐Hf Isotope Tracing

Abstract

A potential zircon reference material (BB zircon) for laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) U‐Pb geochronology and Hf isotope geochemistry is described. A batch of twenty zircon megacrysts (0.5–1.5 cm3) from Sri Lanka was studied. Within‐grain rare earth element (REE) compositions are largely homogeneous, albeit with some variation seen between fractured and homogeneous domains. Excluding fractured cathodoluminescence bright domains, the variation in U content for all analysed crystals ranged from 227 to 368 μg g−1 and the average Th/U ratios were between 0.20 and 0.47. The Hf isotope composition (0.56–0.84 g/100 g Hf) is homogeneous within and between the grains – mean 176Hf/177Hf of 0.281674 ± 0.000018 (2s). The calculated alpha dose of 0.59 × 1018 g−1 for a number of BB grains falls within the trend of previously studied, untreated zircon samples from Sri Lanka. Aliquots of the same crystal (analysed by ID‐TIMS in four different laboratories) gave consistent U‐Pb ages with excellent measurement reproducibility (0.1–0.4% RSD). Interlaboratory assessment (by LA‐ICP‐MS) from individual crystals returned results that are within uncertainty equivalent to the TIMS ages. Finally, we report on within‐ and between‐grain homogeneity of the oxygen isotope systematic of four BB crystals (13.16‰ VSMOW).

SA01 – A Proposed Zircon Reference Material for Microbeam U‐Pb Age and Hf‐O Isotopic Determination

“…Although the seller informed us that the SA01 zircon megacryst was collected from the KwaZulu‐Natal Province, South Africa, zircons with similar geochemical features have not been found in KwaZulu‐Natal so far. As shown in Table , SA01 is quite different from the now fairly large suite of similar aged Sri Lankan zircons that have been published [SL7 (Kinny et al ), CZ3 (Pidgeon et al , Xu et al , Cavosie et al ), M257 (Nasdala et al , Li et al , Hu et al ), BR266 (Stern , Woodhead et al , Liu et al ), BB9 (Santos et al ), GZ7/GZ8 (Nasdala et al ), M127 (Nasdala et al ) and LGC‐1 (Tian et al )]. In this regard, the genesis of the SA01 zircon megacryst may be different from those of the Sri Lankan zircon megacrysts.…”

“…A suitable natural reference material should be homogeneous in both chemical and isotopic compositions at the scale of analysis. Previous studies have identified a number of natural zircons as reference materials suitable for geochronology and isotope geochemistry, including SL7 (Kinny et al ), CZ3 (Pidgeon et al ), SL13 (Claoué‐Long et al ), 91500 (Wiedenbeck et al ), Temora (Black et al ), BR266 (Stern ), GJ‐1 (Jackson et al , Morel et al ), Mud Tank (Woodhead and Hergt ), M257 (Nasdala et al ), Plešovice (Slama et al ), Sri Lanka (Gehrels et al ), OG1/OGC (Stern et al , Kemp et al ), Penglai (Li et al ), Qinghu (Li et al ), OD‐3 (Iwano et al ), M127 (Nasdala et al ), BB (Santos et al , Lana et al ), LGC‐1 (Tian et al ), GZ7/GZ8 (Nasdala et al ), LKZ‐1 (Cheong et al ) and GHR1 (Eddy et al ). However, most of them are either exhausted or have limited availability against the increasing demands of the microbeam laboratories.…”

Petrography, geochemistry and geochronology of the potassic granitoids of the Rio Itacambiruçu Supersuite: implications for the Meso- to Neoarchean evolution of the Itacambira-Monte Azul block

“…U-Pb isotopic compositions were analyzed using a Thermo Scientific Element 2 sector field (SF) ICP-MS equipped with a CETAC LSX-213 G2 + laser ablation system in the laboratory of radiogenic isotopes of DEGEO-UFOP. The GJ1 (Jackson et al 2004) and BB (Santos et al 2017) standards were used to test the validity and reproducibility of the results obtained (supplementary table 1). Data were reduced using the Glitter Shortcut software (Van Achterbergh et al 2001), and all ages were calculated and plotted on concordia diagrams using IsoplotEx 4.15 software (Ludwig 2003).…”

GGR Biennial Critical Review: Analytical Developments Since 2014

“…A new potential zircon RM (Blueberry, BB zircon) from Sri Lanka was recently described by Santos et al . (). This MRM appears to be a suitable material for U‐Pb dating and Hf isotope measurements.…”