Abstract

The modern atmosphere is the product of billions of years of volatile cycling between terrestrial geochemical reservoirs, punctuated by delivery and loss of atmospheric gases due to impacts. This long-term exchange means that the evolution of the atmosphere and the interior of the Earth are coupled. Therefore, exploring the origins and history of atmospheric and mantle volatiles improves our understanding of the geodynamics of the solid Earth and the habitability of the atmosphere. The naturally occurring, stable noble gases (He, Ne, Ar, Kr, and Xe) are a powerful suite of tracers of volatile origins and transport, as their elemental and isotopic signatures preserve a record of both their source and transport history. In this dissertation, I investigate noble gas systematics first in the ancient atmosphere, then in the modern mantle, focusing on two distinct field areas. I then step back from individual systems to investigate volatile exchange between the terrestrial atmosphere and mantle over time through a global model of noble gas transport. Ancient atmospheric gases trapped within natural samples record a progressive depletion in the abundance of xenon (Xe), accompanied by isotopic fractionation, in the Archean atmosphere over time. However, the detailed history of this loss and isotopic fractionation of Xe remains imperfectly constrained, due to both sampling and analytical limitations. In Chapter 2, I investigate cherts from the 3.55-3.26 Ga Onverwacht Group of the Barberton Greenstone Belt, South Africa, in an effort to quantify Xe isotopic fractionation in the Paleoarchean atmosphere. First, I mapped the distribution and concentration of Xe-producing trace elements (Te, Ba, and U) in chert subsamples via secondary ion mass spectrometry. These data were used to estimate the impact of Xe produced in situ by nuclear reactions on the composition of trapped atmospheric gases in cherts. I then paired these data with noble gas isotopic analyses (Ne, Ar, and Xe) and employed the full spectrum of Xe isotopes to determine the degree of Xe fractionation in the ~3.3 Ga atmosphere. The results demonstrate that bulk cherts trap and retain ancient atmospheric noble gases on billion-year time scales. The gases released by step-crushing only exhibit minor inputs from Xe produced by U, Ba, and Te decay; however, the cherts are variably overprinted with modern atmospheric noble gases. Through a multi-component mixing model, I find that the data are consistent with a Paleoarchean (~3.3 Ga) Xe isotope fractionation signature at or exceeding 19‰u-1. Barberton chert Ne systematics may also indicate that the 20Ne/22Ne ratio of the Paleoarchean atmosphere was lower than the modern atmospheric ratio (< 9.7). Investigating the composition of the ancient atmosphere with the full suite of Xe isotopes revealed a more complex history of noble gas exchange in Barberton rocks than has been previously recognized. Mantle-derived rocks sample reservoirs with distinct noble gas isotopic compositions, reflecting variable degassing histories that can shed light on the processing history of the interior of the Earth. Near-ridge hotspots are particularly promising areas to study the volatile compositions of mantle sources, as they present opportunities to investigate multiple mantle reservoirs simultaneously. In Chapter 3, I measured He, Ne, Ar, and Xe in seven mid-ocean ridge basalt glasses from the East Pacific Rise (EPR) and two ocean island basalt glasses from the Easter Seamount Chain (ESC)—a volcanic lineament generated by the Easter-Salas y Gómez (ESyG) hotspot. The low 4He/3He and 21Ne/22Ne of the ESC mantle source is consistent with a plume origin, and the less nucleogenic Ne composition of EPR mid-ocean ridge basalt (MORB) mantle sources relative to that of Atlantic or Indian Ocean MORBs likely reflects the influence of ESyG plume material along the ridge. The 3He/22Ne of the Pacific MORB mantle source in the southern field region contrasts strongly with the 3He/22Ne of samples near the EPR-ESC intersection, which is also consistent with plume-ridge interaction. Distinct mantle compositions north and south of the ESC-EPR intersection could reflect intrinsic heterogeneity in the MORB mantle source or indicate that ESyG material is scattered throughout the ambient mantle underlying the region. Unfavorable mixing systematics and atmospheric contamination prevented determination of mantle source compositions for samples in this study; however, Ar-Xe step-crush data are consistent with the global dataset. Finally, in Chapter 4, I present a forward, numerical model of He, Ne, and Ar exchange between the MORB mantle, the plume mantle, the atmosphere, and the continental crust, to quantify the relative contribution of noble gases from each reservoir to the atmosphere over time. By exploring a wide parameter space of initial compositions, plume source mantle masses, and net continental crustal growth models, I demonstrate that the outgassing associated with mantle plumes is not a negligible source of noble gases to the atmosphere. In all model simulations, combined outgassing of the plume and MORB mantle dominated the atmospheric budget, indicating that atmospheric evolution is more sensitive to the history of mantle outgassing than growth of the continental crust. Input parameters from successful model realizations of an independent, mantle-focused He-Ne-Xe model generated Ar systematics consistent with observations of the mantle. However, no simulation considered in this study simultaneously satisfied both Ne and Ar atmospheric constraints, requiring further model development. Finally, model outputs were used to estimate both the 3He abundance in the MORB mantle and the amount of 14N delivered to the atmosphere by impact degassing.

Committee Chair

Rita Parai

Committee Members

David Fike; Douglas Wiens; Michael Krawkzynski; Sujoy Mukhopadhyay

Degree

Doctor of Philosophy (PhD)

Author's Department

Earth & Planetary Sciences

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

8-13-2026

Language

English (en)

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Available for download on Saturday, August 12, 2028

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Geochemistry Commons

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