A Novel, Laser‐Based Microsampling Technique for Texturally Controlled, Combined and Complementary Sr and Nd Isotope Measurements in Silicate Minerals. Issue 4 (24th October 2022)

• Record Type: Journal Article
• Authors: Logue, Andrew S.; Bybee, Grant M.; Tappa, Michael J.; Baxter, Ethan; Iaccheri, Linda
• Is Part Of: Geostandards and geoanalytical research. Volume 46:Issue 4(2022)
• Page Start: 789
• Page End: 809
• Publication Date: 2022-10-24
• Subjects: microsampling -- laser ablation -- chromatography -- ID‐TIMS -- reference material; Analytical geochemistry -- Periodicals; Géochimie analytique -- Périodiques; 551.9
• DOI: 10.1111/ggr.12459
• Languages: English
• ISSNs: 1639-4488

Abstract

Abstract : The limitations of many in situ microsampling techniques, especially when applied to isotopic analyses, may result in lower measurement precision and limit the ability to compare different isotope systems within the same phase or the same isotope system between phases. High‐precision, combined and complementary isotopic measurements are typically limited to whole‐rock samples or mineral separates at the expense of textural context. We demonstrate that laser ablation instruments could offer an effective, non‐mechanical alternative to micro‐milling for delineating and extracting single crystals, interstitial phases, and sub‐crystal scale features from soluble‐resin thick sections for column chromatography and high precision ID‐TIMS measurement. Systematic testing demonstrated that both modern and legacy laser instruments are capable of ablating through plagioclase, pyroxene and fused glass to depths of 200 μm. Modern instruments offer software benefits to identifying optically‐indistinct petrographic features, chemical zoning and avoiding alteration phases by using overlain high‐resolution datasets. Extracting delineated targets of varying geometry was achieved under binocular microscope using common mineral‐separation tools. Analysis of RM glass used as mineral proxies indicate (a) no significant thermal aureole on ablated margins that could affect measured parent‐daughter ratios, (b) no elevated risk of contamination compared with traditional mineral separation techniques, (c) excellent blanks for low‐yield analyses and (d) high‐precision ID‐TIMS results ( 87 Sr/ 86 Sr and 143 Nd/ 144 Nd) for sub‐100 ng Sr loads and sub‐10 ng Nd loads. Key Points: LA instruments could offer a non-mechanical alternative for delineating and liberating mineral targets. RM glass proxies demonstrated no significant deviation in parent/daughter analyte mass fractions or 87 Sr/ 86 Sr and 143 Nd/ 144 Nd ratios after ablation, extraction and chromatography. This novel method combines the selectivity of LA with the high-precision and multi-isotope abilities of ID-IRMS.