Doctor of Philosophy
Planetary Science and Exploration
Osinski, Gordon R.
Linnen, Robert L.
Impact cratering is a fundamental and ubiquitous geological process on all solid planetary bodies in our solar system. Impacts into carbonate-rich sedimentary target rocks on Earth are still poorly understood. The fate of carbonates during impact, in particular whether they undergo melting or decomposition, is actively debated. The dominant process is significant as decomposition would cause severe climatic effects due to release of large amounts of carbon dioxide into the atmosphere. At the root of the problem is the difficulty to distinguish and characterize the genesis of the variety of impactite carbonates produced. The Haughton impact structure in the Canadian High Arctic was formed in the Paleozoic Arctic Platform which overlies Precambrian metamorphic rocks. In order to better understand impactite formation and hydrothermal mineralization in impacts into calcareous targets, this study conducts a thorough investigation and characterization of the impactites and mineralization at the centre and around the central uplift periphery at Haughton. A variety of petrographic, geochemical and mineralogical techniques are applied to characterize the rocks, including microbeam analysis and cathodoluminescence. Recent shallow drill cores at the centre of structure reveal melt rocks unlike those previously identified at Haughton. The first, is a crystalline carbonate-sulfate-silicate melt rock classified based on a series of igneous textures. The second, is a silicate impact melt rock. Both cores are pervasively hydrothermally altered. Finally, we re-evaluate the hydrothermal mineralization at the centre and periphery within the cores and faulted target rocks. Overall this work confirms the presence of crystalline carbonate melt rocks at Haughton; presents detailed methodologies on how to distinguish between a wide range of carbonate and sulfate impactite products, hydrothermal replacement and diagenetic carbonate; presents an updated hydrothermal model and paragenesis for mineralization at the centre of the structure; and confirms impacts into mixed targets produce heterogeneous impactites and hydrothermal mineralization.
Summary for Lay Audience
Impact cratering is the process through which a projectile from space, such as an asteroid, impacts the surface of a planetary body like Earth. Impacts into igneous or metamorphic rocks such as granite or gneiss, are well understood. Impacts into sedimentary rocks, particularly those rich in volatiles such as carbonate and sulfate, however, are less well understood. Whether these carbonate rocks melt or break down into a carbon dioxide and lime, for example, as a result of the impact is actively debated. The principal challenge lies both in the difficulty to recognize and distinguish between the different carbonate and sulfate rocks produced or altered; and the lack of detailed studies at impact craters hosted in carbonate- or sulfate-rich rocks. The Haughton impact structure in the Canadian High Arctic was formed in a mixture of carbonate- and sulfate-rich rocks from the Paleozoic Arctic Platform and metamorphic rocks. In order to better understand impacts into carbonate-rich targets, this study conducts a thorough investigation and characterization of the rocks from the centre of the Haughton impact and new minerals formed by heated circulating fluids generated by the impact (a.k.a. hydrothermal minerals). A variety of petrographic, geochemical and mineralogical techniques are applied to characterize the rocks. Recent shallow drill cores at the centre of structure reveal two new melt rocks unlike those previously identified at Haughton. The first, is a mixed crystalline carbonate-sulfate-silicate melt rock classified based on a series of textures. The second, is a silicate impact melt rock. Both cores are pervasively hydrothermally altered. Finally, we re-evaluate and create a new model for hydrothermal mineralization within the structure. This study confirms the presence of carbonate impact melt rocks at Haughton; presents detailed methods on how to distinguish between a wide range of pre-, syn- and post-impact carbonate and sulfate products; presents an updated hydrothermal model for mineralization at the centre of the structure; and confirms impacts into mixed types of rocks result in diverse crater deposits and varied mineralization.
Marion, Cassandra L., "Characterization of Impact Melt Rocks and Hydrothermal Mineralization at the Haughton Impact Structure, Devon Island, Canada: An Investigation of Impacts into Carbonate Targets" (2020). Electronic Thesis and Dissertation Repository. 6987.
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Available for download on Thursday, December 31, 2020