2H/1H measurements of amphiboles and nominally anhydrous minerals (clinopyroxene, garnet and diamond) using high-temperature CF-EA-PY-IRMS

Abstract : Rationale: We have used ahigh–precision, high efficiency method for themeasurementof the2H/1H ratios of hydrous silicates (amphiboles) and nominally anhydrous minerals (NAM) such as clinopyroxene, garnet and diamond, which are usually extremely resistant to pyrolysis. This opens up new fields of investigation to better understand the conditionsof formation fordeep-Earth minerals. Method: The technique described hereinvolvesIsotopic Ratio Mass Spectrometry (IRMS) online in continuous flow mode with an Elemental Analyzer (EA) using“purge and trap” technology rather than conventional packed column-GC gas separation. The system is equipped with a special high temperature furnace reaching 1500°C, with a longer hot zone and improved temperature stability. Emphasis is put on the efficiency of the system to reliably pyrolyserefractory minerals difficult to analyse with other conventional systems. Results: While conventional systems usually fail to generate hydrogen suitable for isotopic analyses, with the technique presented here we were able to measure 2H/1H ratios from 4diamond samples (δ2H= -60, -77, -84 and -79‰ V-SMOW; average SD =4.5‰; n=2),3 garnet samples (δ2Hfrom -70 to -63‰), and 9 clinopyroxenes (δ2H from -92 to -58‰) associated with7 amphiboles (δ2Hfrom -76 to -27‰) from single mantle rock. Conclusions: The possibility of using such a system to reliably measure 2H/1H ratios from refractory minerals, which are usually extremely difficult to analyse, offers a new tool of investigation for giving us unrivaled clues to study the Earth's deep interiors.
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François Fourel, Christophe Lécuyer, Attila Demeny, Philippe Boulvais, Lutz Lange, et al.. 2H/1H measurements of amphiboles and nominally anhydrous minerals (clinopyroxene, garnet and diamond) using high-temperature CF-EA-PY-IRMS. Rapid Communications in Mass Spectrometry, Wiley, 2017, 31 (24), pp.2066-2072. ⟨10.1002/rcm.7996⟩. ⟨insu-01596692⟩



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