Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Geophysics

Supervisor

Quesnel Yoann

2nd Supervisor

Osinski Gordon R.

Co-Supervisor

Abstract

Hypervelocity impact craters are the most abundant morphologic features on rocky planetary bodies of the Solar System, except on Earth where they have mostly been erased by plate tectonics, erosion, or are buried under sediments. The internal structure of complex impact craters can only be studied on Earth by using ground-truth geophysical and geological studies. Such approaches - combined with modeling - can reveal how impact cratering, target geological composition, erosion and other post-impact processes can lead to the observed geophysical anomalies, which could also be detected by remote geophysical data on other planetary surfaces. In this work, a multidisciplinary approach is conducted by coupling geological data to field and laboratory geophysics. Magnetic field mapping, gravimetry measurements, electromagnetic soundings (EM34), paleomagnetic analyses, rock magnetism and petrography techniques are used. Four impact structures in Canada are studied: Haughton, Tunnunik, West and East Clearwater Lake. For the first time, we reveal that the recently-discovered Tunnunik impact structure has typical negative gravity and positive magnetic field anomalies, which help us to reconsider the brecciation extent in the target rocks. The 20 km diameter Haughton crater, which is less eroded than Tunnunik, shows evidence for an enhanced-magnetization in the core of the central uplift, caused by impact-generated hydrothermal alteration. Some samples of the Clearwater Lake impact structures in Québec are also studied with paleomagnetism, which helps to constrain the different ages of the East and West Clearwater Lake impacts. This work has important implications for our understanding of impact-cratering in the Solar System, especially concerning the study of planetary surfaces. The important roles of post-impact processes such as alteration and erosion on geophysical anomalies, petrophysical properties and morphometry of complex impact structures are also discussed in detail, suggesting that such effects should be more studied and quantified in future works.

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