Noble gas isotopic signatures of deep Earth reservoirs reflect primordial volatiles delivered during accretion, along with radioactive decay products and atmospheric volatiles added to the mantle over Earth history. Noble gases serve as powerful tracers of volatile accretion and transport over time. Ratios of primordial (
i.e., stable, non-radiogenic) noble gas isotopes provide fingerprints of volatiles delivered by different precursor components to the growing Earth. Radiogenic noble gas isotopes provide constraints on the timing and extent of volatile transport between the deep Earth and surface reservoirs over Earth history. The short-lived, extinct I-Xe and Pu-Xe systems are sensitive to degassing that occurred during the Hadean, and preserve signatures of ancient mantle heterogeneity [1]. Long-lived extant systems (e.g., U-Th-He-Ne-Xe) generate signatures that reflect long-term degassing. Regassing, or injection and incorporation of compositionally distinct atmospheric noble gases, also affects mantle isotopic compositions. Thus, noble gas isotopes measured in mantle-derived samples provide constraints on volatile delivery during accretion and transport processes among terrestrial reservoirs on a broad range of timescales.
The plume source mantle noble gas isotopic signature is consistent with limited volatile loss to the surface in association with plate tectonics when compared to the upper mantle sampled by mid-ocean ridge volcanism [1-5]. Plume Xe isotopic signatures indicate limited degassing compared to the upper mantle, as well as a significant contribution of regassed atmospheric Xe [1,4,5]. Here, He, Ne and Xe isotopic compositions in plume-influenced samples are used to constrain the history of volatile accretion and the long-term transport of volatiles between the plume source mantle and surface reservoirs.
[1] Mukhopadhyay, Nature, 2012; [2] Farley et al., EPSL 1992; [3] Graham, RIMG, 2002; [4] Pető et al., EPSL, 2013; [5] Parai et al., Lithos, 2019.
