Doctor of Philosophy
Planetary Science and Exploration
Neish, Catherine D.
Osinski, Gordon R.
The emplacement mechanisms of lunar impact melt flows, that form from hypervelocity impact events, have been a subject of debate in the lunar science community, because of their unique physical properties that separate them from other geologic features. Understanding how lunar impact melt flows were emplaced on the surface of the Moon will not only grant us new information about the flow dynamics of impact melt but provide insight into the production and distribution of impact melt and how it built and modified the surfaces of planetary surfaces.
Lunar impact melt flows exhibit surface roughness textures and morphologies that are analogous to terrestrial lava flows. For this reason, we seek to quantify the surface roughness of terrestrial lava flows using synthetic aperture radar (SAR) at two localities, Craters of the Moon National Monument and Preserve, Idaho and the 2014-2015 Holuhraun lava flow-field. We focus on using SAR data in this study for two reasons, (1) improve our understanding on how radar surface roughness can be connected to the emplacement mechanisms of volcanic and impact melt, and (2) to highlight the techniques capabilities and limitations for differentiating different lava flow types and lava facies. Impact melt has contrasting intrinsic properties and geologic origins to lava flows, so we include the analysis of a physical property of impact melts that influences melt behaviour. To complement our radar surface roughness analysis, we seek to constrain the temperature of the Mistastin Lake impact structure impact melt deposits by analyzing the crystallographic orientations and microstructures of zircon grains and zirconia crystals encased in melt-bearing impactites. We demonstrate in this work that without entirely understanding the capabilities and limitations of using SAR for lava flow differentiation, we will struggle to interpret the eruption dynamics and history of volcanic landforms on terrestrial bodies, which in turn limits what we can learn about impact melt emplacement. Furthermore, we discover that high temperature and pressure conditions can be constrained from an impact environment that was once superheated, which has strong implications for discovering high P-T shock indicators in other terrestrial impact structures and also in lunar impactites. In addition, our work has strong applications towards addressing high priority science goals established by research groups such as the Lunar Exploration Analysis Group.
Summary for Lay Audience
During impact events on a planetary surface, an immense amount of energy is released, shocking, melting, and vapourizing surrounding rocks and minerals. The rocks and minerals that melt produce material known as impact melt, which is observed in and around impact craters on rocky bodies throughout our Solar System. On the Moon, we observe some of these impact melts as lava-like flows moving downslope within and outside of impact craters. These lava-like features are known as lunar impact melt flows. Understanding how they were emplaced on the lunar surface is regarded as an important topic to study in planetary science since the production and distribution of impact melt can provide insight into how impact cratering processes have altered the surfaces of planetary bodies during the early age of our Solar System. In this work, we focus on studying the surface roughness of terrestrial lava flows using radar data and estimating the formation temperatures of terrestrial impact melt deposits. We included two studies on terrestrial lava flows and impact melt deposits because each of these geologic features offer a different piece of information about melt emplacement (how it was placed on the surface). The surface roughness of a lava flow is connected to how it was placed on the surface during a volcanic eruption. If we can understand how different lava flows were emplaced on Earth using radar and other remote sensing techniques, then we can gain new insights into the emplacement of lunar impact melt flows with similar surface roughness characteristics. The temperatures of volcanic and impact melt strongly influence their flow behaviour on a surface. Due to impact melt temperatures being significantly higher upon formation as compared to lava flows (>1700°C vs 1200°C), we must understand the range of temperatures impact melts can have when they form during impact events. We demonstrate in this work how we can study and infer the emplacement of terrestrial lava flows using radar data, and how we can provide a much clearer picture of the temperature conditions of impact melt deposits. Moreover, we also stress the importance of terrestrial analogue research, and how our work can contribute to high priority lunar science and exploration goals established by NASA and other space agencies.
Tolometti, Gavin Douglas, "The Physical Properties of Volcanic and Impact Melt" (2021). Electronic Thesis and Dissertation Repository. 7972.