Investigation of the impact-generated hydrothermal system at the West Clearwater Lake impact structure, Quebec, Canada

Juan Pablo Jaimes Bermudez, The University of Western Ontario

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.