Surface Evolution on Basaltic Bodies: Tectonic, Geomorphic, and Diagenetic Modification on Io and Mars

Citation

Seeger, Christina Hope (2025) Surface Evolution on Basaltic Bodies: Tectonic, Geomorphic, and Diagenetic Modification on Io and Mars. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/4mfp-zx56. https://resolver.caltech.edu/CaltechTHESIS:06022025-233903333

Abstract

All planets and moons in the Solar System evolve over geologic timescales, though the processes affecting each body vary widely depending on gravity, atmosphere thickness and composition, volcanic activity, and perhaps most importantly, the presence of a hydrologic cycle. This dissertation investigates the surface evolution of two basaltic bodies in our Solar System: one that has barely changed in 3.5 billion years, and one that changes almost daily. Jupiter’s moon Io is continually resurfaced by large-scale volcanic eruptions of low-viscosity lava and sulfur dioxide gas, driven by interior heating generated by diurnal tidal stresses. Such tidal stresses have been linked to eruptive activity and tectonic ridge formation on other moons like Titan and Europa; while they strongly influence Io, they are orders of magnitude weaker than the crustal subsidence stresses which control the expression of tectonic features on the surface (kilometers-tall mountains and caldera-like volcanic features called paterae). Chapter 2 investigates whether tidal stresses may have any influence on the formation of mountains and paterae. Though no global trends have been identified, I suggest that local correlations between patera orientations and the large volcanic center of Loki Patera may provide insight into the magma plumbing pathways of this unique volcano. As soon as tectonic mountains are uplifted on Io, they are subject to gravity- and seismicity-driven erosional processes tearing them down. In Chapter 3, I present the first regional geologic map of a trio of mountains named Cocytus Montes and identify a new geologic unit—a blocky deposit composed of kilometer-scale slab-shaped blocks of crust—that are visible thanks to the favorable resolution and near-terminator lighting conditions of new Junocam imagery. I explore several new erosional mechanisms for Io that could create these blocks, determining regolith creep-modified cliff collapse to be the most likely. The orders of magnitude higher resolution imagery collected by the Mars Science Laboratory Curiosity rover provides a backdrop for much closer analysis of how sediments moved, deposited, lithified, and were subsequently modified by diagenetic fluids on ancient Mars. Chapter 4 takes advantage of hand-sample scale data to categorize a diverse array of diagenetic fabrics (nodules, pits, color variations) that correlate with the stratigraphy in a region defined by a transition from clay-bearing rocks to sulfate-bearing rocks. I present several hypotheses to explain how the Mg sulfate detected in these nodules and pore-filling cements may have precipitated at depth, to complement current evaporite-driven models. These hypotheses could be tested in the coming years of Mars exploration by the rover, and will provide insights into the longevity of a groundwater system after surface water ceased to flow on ancient Mars. Overall, this work explores the well-studied terrestrial processes of surface modification, degradation, and diagenesis under distinctly alien conditions throughout the Solar System.

Thesis Files