In situ Rb–Sr beryl geochronology by LA-ICP-MS/MS

Abstract

Beryl is a principal beryllium (Be) host in diverse geological settings, including pegmatite, mica schist, and tungsten (W)–tin (Sn) systems (typically as high-temperature hydrothermal veins), and may occur at metasomatic contacts between igneous intrusions and gneiss, schist, or carbonate rock. Despite extensive work on mineralogy and trace element systematics, the geochronological potential of beryl remains underexplored. Here, we establish and validate an in situ Rb–Sr dating protocol for beryl using LA-ICP-MS/MS. Eight natural beryl samples spanning 1.8–0.14 Ga with Rb contents of 30–500 ppm were analyzed. Samples YYX241, M6548, M7971, and WLST181 exhibit relatively low common-Sr contents from 0.64% to 11.4%, whereas HJLG241, CHY241, MFS251, and SHY241 display elevated and variable common Sr contents from 12.0% to 29.4%. Isochron-based evaluations show that in situ beryl Rb–Sr ages are precise and accurate and consistent with solution Rb–Sr results or U–Pb ages of coexisting accessory minerals, while providing high spatial resolution and analytical throughput with high efficiency and resolution. We additionally assess the Rb–Sr closure temperature in beryl. To facilitate routine application, we present a data reduction scheme (DRS) named “Visual Rb–Sr age” and a visual (inverse) isochron Rb–Sr simultaneous age with an initial Sr plug-in for Iolite to process in situ datasets. On the basis of isotope-dilution mass spectrometry (ID–MS) isochrons, beryl samples HJLG241 and CHY241, yielding Rb–Sr ages of 1793 ± 13 Ma (2s, n = 5) and 1835 ± 8 Ma (2s, n = 5), respectively, are proposed as candidate reference materials for microbeam Rb–Sr geochronology. These results demonstrate that direct Rb–Sr dating of beryl and its gem varieties (aquamarine, emerald, heliodor, goshenite, morganite, and red beryl) can provide independent age constraints that strengthen provenance and timing assessments in beryl-focused geochemical studies.