Geochronology and beyond: new applications of LA-MC-ICP-MS/MS
Abstract
The development of tandem mass spectrometers equipped with collision cells has enabled online interference removal for ICP-MS, with special attention paid to beta decay systems used for geochronology (e.g., Rb-Sr, Lu-Hf). The addition of pre-cell mass filters and collision cells for multicollector mass spectrometry has recently been utilized to constrain single laser spot Rb-Sr isochron dates in biotite with unprecedented precision [1]. This technique opens up avenues for campaign-style Rb-Sr geochronology, and adds a powerful new tool for constraining the cooling history of rocks in many tectonic settings over a broad range of spatial and temporal scales. Static multicollection from 85Rb to mass-shifted 88Sr19F utilizing the Thermo Scientific™ Neoma™ MC-ICP-MS/MS coupled to an ESL™ imageGEO™193 excimer laser-ablation system enables the recovery of significant age information from individual integrations within single laser spot analyses. These data reveal single spot isochrons - some with multiple isochronous populations - from multiple orogenic belts. The high-precision simultaneous isotope measurement approach on the Neoma™ enables determination of distinct initial 87Sr/86Sr ratios based on the fit of individual isochrons within single laser spots, which is assisted by the use of 1011 and 1013 ohm amplifiers on Faraday cups. The large range of Rb/Sr ratios in micas opens up a new microsampling frontier for isochron-based geochronology that will transform our approach to unraveling continent-scale tectonic processes over Earth's history. Two extensive datasets from these efforts demonstrate punctuated geochronologic events not captured by other chronometers, suggesting the ability to uncover previously hidden thermal and fluid events using our approach. Looking toward the future, novel applications of LA-MC-ICP-MS/MS will expand many fields that utilize high precision isotope geochemistry, including geochronology, biology, and nuclear forensics. For example, initial successes employing single collector MS/MS machines for in situ Lu-Hf analyses open the door for vastly improved precision by LA-MC-ICP-MS/MS, particularly on the Hf isotope ratio in low-Hf phases such as garnet. [1] Cruz-Uribe et al. (2023) Geostandards and Geoanalytical Research. doi:10.1111/ggr.12518
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2023
- Bibcode:
- 2023AGUFM.V24A..04C