The thermal and mechanical structure of stable continental lithosphere within a dynamic mantle
Cooper, Catherine Marguerite
Doctor of Philosophy
Understanding the interaction between continental lithosphere and the convecting mantle is not only important for determining the thermal structure and the role of continental lithosphere in the Earth's heat loss system, but also for determining the deformation response of continental lithosphere. This thesis presents the results from numerical simulations and scaling analyses for two studies that solve for: (1) the thermal structure of stable continental lithosphere within a dynamic mantle and (2) the stability of a chemical layer within a convecting mantle. The thermal structure of stable continental lithosphere is determined by its thermal properties as well as by the input of heat from the convecting mantle. The first study varies the total amount and distribution of crustal heat production, as well as lithospheric thickness, while maintaining a coupled heat loss system between the continental lithosphere and convecting mantle. Doing so confirms that the local thermal structure of stable continental lithosphere and surface heat flow variations strongly depend on the total amount and distribution of crustal heat production. Furthermore, the mantle heat flux remains low and constant for variable heat production values and distributions regardless of the presence of a cratonic root. In addition, the chemical component of the stable continental lithosphere regulates the thickness of the thermal lithosphere, influencing deep thermal structure. The second study focuses on the deformation response of a chemical layer when emplaced in the upper thermal boundary layer of the convecting mantle. The manner in which a chemical layer deforms depends on the tradeoff between its intrinsic properties, such as buoyancy, viscosity and yield strength, and the deforming power of the convecting mantle, these being the parameters varied in the study. Scaling relationships extended the results from the numerical simulations to parameters beyond computation capabilities. This study provides analogs for many geologic processes that are dependent on lithospheric deformation. The second study concluded that as mantle convective vigor increases, the required buoyancy of the chemical lithosphere required for stability decreases, as does the yield stress. The viscosity of the chemical lithosphere required for stability depends on its initial volume and weakly on the mantle's convective vigor.