Thesis defense of Jonathan Poh

Precambrian deformation zones in compressive tectonic regimes: A numerical perspective in relation to the Athabasca Basin and its implication to uranium mineralisation

Abstract

The two tectonic styles that occur throughout the Earth's evolution can be categorised based on their structural and metamorphic specificities, age of the geological localities and the strength of the associated lithosphere. With such contrasting deformation profiles, the extent of the structural inheritance would impact the location for future mineral deposits. This was suggested to apply to the Athabasca Basin and the genesis of the uranium deposits. These deposits resided within a large structural corridor at the eastern extent of the Athabasca Basin. The genesis for these structures was interpreted to be a product from a major Paleoproterozoic orogen, the Trans-Hudson Orogeny (2.07 to 1.79 Ga). To investigate the relevance of these inherited structures and their role in mineral deposits, classical numerical techniques were used to verify tectonic models of varying configurations. This dissertation was conducted in three parts. The first part pertains to knowing the physical conditions required to generate structures that correlate to the structural corridor. Two broad crustal deformation styles were characterised and verified the physical feasibility of a recent tectonic model (Pop-down tectonics). The second part focused on identifying a transition between the two broad tectonic styles seen throughout the Earth's history. This was conducted with the testing of the four parameters (strain-rate, thermal profile, crustal rheology and crustal radiogenic heat production) essential to the strength of the lithosphere. Results indicate that such a transition exists and is linked to the maximum crustal strength at the first order. The final part focused on how the inherited structures aided in the preparation of the geological environment for mineral deposits. This part was conducted using fluid-thermal modelling techniques. Results suggested that the inherited structures operated as fluid-thermal conduits that facilitate the mixing of basinal and basement-hosted fluids with robust convection cells. This was identified as an essential process for uranium mineralisation. These findings indicated the significance of structural inheritance from preceding orogenic activities for mineral resources. Further exploration targeting would require an upscaling to provincial scale to further characterise these inherited ancients structures and potential paleo-plate boundaries.