Simultaneous In Situ Determination of Pb Isotope Ratios and Trace Element Concentrations in Melt Inclusions by LASS-ICP-MS

Melt inclusions provide unique insights into magmatic sources and processes. This study presents a method for simultaneously measuring Pb isotopes and trace elements in melt inclusions using a 193 nm excimer laser ablation system coupled to a multiple-collector inductively coupled plasma-mass spectrometer (MC-ICP-MS) and a sector-field ICP-MS (SF-ICP-MS). The ablated aerosol was split with a Y-shaped connector into two gas streams, which were simultaneously transported into two mass spectrometers. Lead isotopes were measured on the MC-ICP-MS, while trace element concentrations were determined on the SF-ICP-MS. Little analytical bias was observed when the aerosol is divided into variable proportions (5:5, 6:4, 7:3, 8:2-9:1) to the two instruments. The precision and accuracy of this method were evaluated by analyzing five geological reference glasses with two laser spot diameters (33, and 45 mu m). All the 33 measured trace element concentrations are consistent with the reference values (+/- 10%) and have precisions less than 15% (2RSD). The precisions of the Pb-208/Pb-206, and Pb-207/Pb-206 ratios correlate with Pb concentrations. From BHVO-2G (Pb = 1.6 ppm) to TB-1G (Pb = 16.1 ppm), the precision on these ratios improve from about 0.4%-0.2% with a 33 mu m laser spot diameter. The mean Pb isotope ratios for the five reference glasses are within 0.15% of the reference values. Using our new method, Pb isotope ratios and trace element contents of plagioclase-hosted melt inclusions in a mid-ocean ridge basalt from the Indian Ocean were measured.

Automated summary

This study presents a method for simultaneously measuring Pb isotopes and trace elements in melt inclusions using a laser ablation system coupled to multiple ICP-MS instruments. The method showed little analytical bias and high precision when analyzing geological reference glasses. The Pb isotope ratios and trace element contents of plagioclase-hosted melt inclusions were successfully measured using this method.