Trace element homogeneity from micron- to atomic scale: Implication for the suitability of the zircon GJ-1 as a trace element reference material

Abstract

Trace element homogeneity from micron-to atomic scale: Implication for the suitability of the zircon GJ-1 as a trace element reference material. Highlights The zircon reference material GJ-1 shows micron-to atomic scale chemical and structural homogeneity  GJ-1 can be used as a reference material for U-Th-Pb dating and Lu-Hf isotopic studies, but also for trace element analysis  GJ-1 combines structural and chemical homogeneity with chemical abundance and large sample size and volume  Atom probe tomography allows assessment of atomic scale chemical homogeneity of minerals e.g. reference materials Keywords zircon, reference material, trace elements, atom probe tomography, nanometre scale, GJ-1 AbstractThe quality of a chemical reference material relies on the fact that the composition of the material is homogeneous across all scales. A series of different techniques have been used to evaluate the trace element homogeneity of the GJ-1 reference zircon from the micron -to atomic scale. Cathodoluminescene imaging was conducted along with quantitative crystallographic orientation analysis and trace element analysis using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). The nanometre-scale homogeneity was evaluated by analysing five mineral tips using atom probe tomography, which provides atomic scale three dimensional chemical reconstructions with unprecedented spatial resolution. Results show that the GJ-1 reference zircon is homogeneous at all scales, both structurally and chemically. Crystallographic orientation data confirms that this gem quality zircon has no detectable internal crystallographic orientation changes such as crystalplastic deformation features or cracks. No mineral inclusions were found. Atom probe tomography shows that there is a lack of any chemical clustering or other modes of spatially defined elemental accumulation or depletion for the most abundant trace elements such as Y, Yb and Hf. This finding is supported by LA-ICPMS data revealing homogeneity within the analytical precision. Trace elements of significant abundance include P, Yb, Y, U and Hf, with contents of 30±6, 65±2, 238±5, 284±14 and 6681±57ppm, respectively. Hence, the GJ-1 zircon used as a reference zircon for U-Pb and Hf-isotopic studies is also a suitable zircon reference material for trace element analyses.

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

“…In spite of significant differences in trace element mass fractions, different SA01 zircon shards are characterised by consistent chondrite‐normalised REE patterns, namely depletion in LREE, enrichment in HREE, positive Ce anomaly and negligible Eu anomaly. Compared with the widely used zircon reference materials 91500 (Wiedenbeck et al ), Mud Tank (Woodhead and Hergt ), CZ‐3 (Pidgeon et al ), OG1 (Stern et al , Kemp et al ), Temora (Black et al ), Plešovice (Slama et al , Ver Hoeve et al ), GJ‐1 (Jackson et al , Piazolo et al ), GZ7/GZ8 (Nasdala et al ) and Qinghu (Li et al ), SA01 zircon is distinct with high Ti mass fractions and Th/U ratios (Figure f; Kirkland et al ). It is very common that zircons crystallised in alkaline magmas have high Ti mass fractions and high Th/U ratios (Fu et al , Peng et al , Zhu et al ).…”

“…Chondrite‐normalised REE patterns of intra‐grain analyses of three shards in (a–d) session 1 and (e) 2; (f) Th/U ratios versus Ti contents (μg g −1 ) of different zircon reference materials and SA01 zircon (data for zircon reference materials are from Li et al , Kirkland et al , Piazolo et al , Nasdala et al , and Ver Hoeve et al ; alkaline rocks data from Peng et al ). [Colour figure can be viewed at wileyonlinelibrary.com]…”

Atomic worlds: Current state and future of atom probe tomography in geoscience

“…In particular, zircon and badelleyite reference materials have been used to confirm chemical quantification and to optimise acquisition conditions for these minerals [18,43 46]. Conversely, APM has been employed to test the nanoscale homogeneity of existing geostandards [47]. Others have also reported comparisons between APM chemical and isotopic compositions with those from standard materials or other well-characterised samples [26,28,32].…”

“…Recent work has shown that chemical values derived from APM of zircon, at length scales of the specimen needle and below, are precise and reasonably accurate, though minor artefacts may arise depending on the analysis conditions [44,46]. A current effort from eight APM laboratories around the world is investigating these effects systematically using a reference material used in zircon geochronology [47], which has been shown to be chemically homogeneous at the nanometer scale. In the future, such rigorous evaluation of the accuracy of APM data will be necessary for other minerals.…”

Advances and Opportunities in Ore Mineralogy

“…APT couples chemical sensitivity and three-dimensional capabilities with a spatial resolution near the atomic scale to provide unique information about nanoscale structures. The technique has been demonstrated as a valuable tool to complement SIMS and allow for smallest-scale geochronology (e.g., [103]), to understand nanoscale diffusion within zircon [104,105], and for the examination of homogeneity within geochronological reference materials [106].…”