Bachelor of Arts
McConnell, Thrust, Limestone, Sandstone, Fluids, Alberta, Cataclasites
Fault rocks from the McConnell thrust consist of limestone mylonite, carbonate and shale cataclasites, and deformed sandstones. The limestone mylonite in the hanging wall mayor may not show different levels of cataclastic overprint. Just below these hanging wall rocks is a zone of comminuted material. This zone contains cataclasites that are produced by the mixing of hanging wall and footwall materials. Underneath this unit are the shale cataclasites of the footwall and beneath this are deformed sandstones that become progressively less deformed further from the fault zone. Based on microstructural evidence these rocks show cycles of mesoscopically brittle and ductile deformation. Veins and fractures exhibit cycles of compression and extension suggesting that some parts of the fault move at different speeds than other parts. Fluids play important roles in fault processes, and one significant source of fluids is the conversion of smectite clays to illite clays, which often accompanies faulting. This reaction liberates interlayer water resulting in a solid volume loss of 33-47%. Shearing of muds results in a permeability change followed by a dewatering event and collapse of the layer. These two processes work in conjunction to deplete the shale layer through time. Build up of pore fluids and dewatering results in softening and hardening of the shales respectively. This may cause more or less deformation to be localized in the shales. Fluids expelled from shales may undergo advection to the hanging wall, locally increasing pore pressures, and initiating a short burst of mesoscopically brittle failure in the hanging wall. Thus footwall lithologies can play a crucial role in determining deformation styles and geometries of the hanging wall.
Miyagi, Lowell, "Microstructures and Deformation in Some Fault Rocks From The McConnell Thrust at Mount Yamnuska (Alberta): Implications for Fluid Flow and Faulting and Cycles of Strain-Hardening and Softening" (2004). Honors Papers. 492.