Mercury's global evolution : elucidating the tectonic, volcanic, and early magnetic field history through observations and numerical modeling

The MESSENGER mission from 2008-2015 yielded a wealth of information about our innermost planet, Mercury. For the first time, visible images of the entire planet, measurements of topography, global characterization of the gravity and magnetic fields as well as surface composition, were all acquired. From these observations, multiple enigmatic aspects regarding the geological evolution of Mercury emerged: The early evolution was dominated by crustal production and creation of the Intercrater Plains by extensive effusive volcanism covering the planet until ~4.0 billion years ago (Ga). This was followed by spatially localized effusive volcanism until ~3.5 Ga that created the Smooth Plains, by global contraction that resulted in a unique global distribution of thrust-fault related landforms called shortening structures, and an early internally-driven magnetic field at ~4.0-3.5 Ga producing crustal magnetization detectable from orbit. In this thesis, I focus on the origin and driving mechanism(s) of each these observations. First, I constrain and investigate the formation of shortening structures in the Smooth Plains. I compile a new comprehensive database that characterizes the morphology of shortening structures and provide the first statistical analysis of variations in morphological characteristics across the entire planet (Chapter 2). Second, areal strain estimates (Chapter 2), and numerical modelling of the surface morphology of Smooth Plain’s shortening structures to constrain the subsurface fault structure (Chapter 3), both require large compressional stresses. These stresses are attributed mainly to 5-10 km of global contraction due to secular cooling of the planet, rather than to bending stresses from volcanic loading by ~1-4 km of basalt as previously assumed. Lastly, I revisit the thermal evolution of Mercury (Chapter 4) and propose the first self-consistent model that matches the newly-constrained geologic record. I focus on a novel way to incorporate the thermal consequences of magmatism and crustal production to form the Intercrater and Smooth Plains. Here, I show that voluminous crustal production can drive a period of strong mantle cooling that both favors an ancient thermally driven dynamo, 5-10 km of radial contraction of the planet, and crustal production.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat