Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Geology

Collaborative Specialization

Planetary Science and Exploration

Supervisor

Osinski, Gordon R.

Abstract

Hypervelocity impact cratering is a ubiquitous and fundamental geologic process that shapes the surface of all solid bodies in the solar system. Despite its catastrophic consequences, it has been shown that under the presence of H2O (liquid or frozen), a heat source, and a permeable substrate, transient impact-generated hydrothermal systems may develop. These hydrothermal systems can alter the mineralogical and geochemical characteristics of the host rocks. Moreover, they provide insight into planetary habitability and past climates, which makes impact craters prime exploration targets on other solid bodies, particularly Mars. Understanding the processes and conditions (temperature, pressure, salinity, pH, and fO2) through which alteration minerals form on terrestrial impact structures has significant implications for the search of habitable environments on Mars, understanding Mars’ paleoclimate, selecting exploration targets for future missions, and improving the interpretations made from orbital observations. This thesis presents a case study of impact-generated hydrothermal alteration of impact melt rocks at the West Clearwater Lake impact structure, Quebec, through optical microscopy, electron microprobe analysis (EPMA), micro X-ray diffraction (μXRD), and Raman spectroscopy. The alteration minerals are predominantly hematite, talc, and quartz. Hematite occurs in four different styles: as replacement of titanomagnetite (Type 1), as pervasive acicular crystals (Type 2), as crystals growing inside amygdules (Type 3), and as colloform bands in veins (Type 4) in association with goethite and quartz. Talc and saponite occur in reaction rims around quartz vugs and predominantly in amygdules in association with type 3 hematite and quartz. This study reveals that the alteration mineralogy and their textural relationships are the result of a changing fluid composition and a decrease in fluid temperature and shows that detailed microscopic observations are required to truly understand the textural complexity under which these minerals form. These findings provide insight into the origin of minerals indicative of water on Mars and the relevance of impact structures as recorders of these processes.

Summary for Lay Audience

Impact cratering, a process through which a planetary object impacts the surface of a solid body, is the most common geologic process in the solar system. Despite the long-recognized devastating consequences of an impact event, in the long term they can create environments that are favorable for life to thrive. Transient impact-generated hydrothermal systems, one of these favorable environments, may form when there is a water source (liquid water or ice), enough heat, and fluid flow conduits. Impact-generated hydrothermal systems may have also formed on the surface of Mars and any other water-bearing rocky bodies. However, detecting and studying these systems requires detailed microscopic textural and chemical analyses. Currently, information from other planetary surfaces is limited to satellite and rover observations, which greatly affects our ability to study in detail these rocks. Therefore, terrestrial analogues are needed to understand how these processes may occur on Mars and elsewhere in the solar system. This thesis investigates the hydrothermal system preserved within the 286-million-year-old, 36 km-diameter West Clearwater Lake impact structure in Quebec, Canada. The focus of this study is the characterization of the alteration mineralogy, in particular the origin of hematite and hydrated phyllosilicates. These two groups of minerals are common on impact craters on Earth and Mars and may indicate the presence of water. This work provides insight into the origin of minerals indicative of water on Mars, shows that detailed analyses are required to understand their origin, and showcases the relevance of impact structures as recorders of these processes.

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