Large-scale volcanism on the terrestrial planets

Evidence for mafic volcanism has been found on each planet in the inner Solar System. Lava flows on these planets range in size from 10s to 1000s of kilometers in extent. I investigated large-scale lava flows on Mercury, Earth, and Mars throughout the chapters in this dissertation. Each of these lava flows provides an avenue to study the emplacement and evolution of lava on various planets and under differing conditions, the factors that affect their overall extent, and potential source areas.

Chapter One investigates large-scale lava flows in the Cerberus region on Mars, specifically to understand their emplacement history, material properties, and possible magma sources. Mapping and crater counting are used to investigate these flows. The derived absolute age estimates suggest an anomalous trend of decreasing ages with increasing distance from the flow source. Through pi-group scaling, changes to the material properties of the lavas during emplacement are identified as the cause for this decreasing age trend and are attributed to increased strength, and decreased porosity, of the lava. These newly derived absolute age estimates are also used to infer the source of the magma feeding these young and extensive lava flows originated below the Cerberus region.

Chapter Two focuses on long and areally extensive lava flows on Earth and Mars, in order to determine the effect of viscosity on the emplacement of 1000+ km flows. In particular, low viscosity lavas are expected to generate such large lava flows. The terrestrial and martian lava flows are interpreted to have been emplaced rapidly, with their final extents limited by the total erupted volume of lava. Through computer modeling, simulations are performed to determine the viscosity values responsible for the observed lava flow extents. The results of this work support low bulk viscosities that correspond to a basaltic composition produce the best reproductions of the martian flows.

Chapter Three investigates volcanism on Mercury, which hosts broad smooth plains in three locales, which have varying interpretations for their emplacement, though volcanic processes are favored. The smooth plains units located in the annulus surrounding the Caloris impact basin contain intermingled high-reflectance red and low-reflectance blue plains. Mapping, crater counting, and spectral analyses are used to suggest the emplacement mechanism for these smooth plains. The results of this work support a volcanic origin, though impact related processes cannot be discounted.