Vesicle-Specific Noble Gas Analyses of "Popping Rock": Implications for Primordial Noble Gases in Earth

Abstract

Gases trapped in individual vesicles in the volatile-rich basaltic glass “popping rock” were found to have the same carbon dioxide, helium-4, and argon-40 composition, but a variable ⁴⁰ Ar/ ³⁶ Ar ratio (∼4000 to ≥40,000). The argon-36 is probably surface-adsorbed atmospheric argon; any mantle argon-36 trapped in the vesicles cannot be distinguished from an atmospheric contaminant. Consequently the ⁴⁰ Ar/ ³⁶ Ar ratios and ³ He/ ³⁶ Ar ratios (1.45) determined are minimum estimates of the upper mantle composition. Heavy noble gas relative abundances in the mantle resemble solar noble gas abundance patterns, and a solar origin may be common to all primordial mantle noble gases.