Bachelor of Arts
Low-temperature deformation, Fault rocks, Thrust faults, Geology, Structural geology
This study analyzes the low-temperature deformation of fault rocks associated thrust faults. Each fault has dominantly carbonate rocks in one wall and dominantly siliciclastic rocks in the other. The rocks from the Hunter Valley and Copper Creek thrusts of the Southern Appalachians, and McConnell thrust of the Canadian Rockies, were analyzed using data extracted at the thin section and SEM scale. The rocks, all of which featured a fine-grained carbonate matrix surrounding larger carbonate and siliciclastic carbonates, all experienced general shearing, but deformed by different deformation mechanisms. The Hunter Valley and McConnell samples showed evidence of cataclasis, diffusive mass transfer, diffusion accommodated grain boundary sliding and, in the case of the Hunter Valley fault rocks dislocation creep. The Copper Creek samples, by contrast, deformed primarily via plastic processes such as diffusion mass transfer and dislocation creep, and showed no evidence of cataclasis. Within the Hunter Valley and McConnell fault rocks, brittle processes such as cataclasis seemed to dominate at the thin section scale but SEM data supported ductile deformation of the fine matrix material. In each case, analysis of fabrics defined by grain orientations found that the rocks were deformed under general shear conditions and moderate convergence angles, although the Hunter Valley rocks showed evidence for a strong simple shear component of strain and relatively low (37° to 48°) while rocks from the Copper Creek and McConnell thrusts experienced roughly equal pure and shear strain components and showed evidence for higher convergence angles (51° to 59° and 61° to 68°, respectively). The findings of this study highlight the complicated nature of fault rock deformation as well as the difficulty of situating fault rocks within schemes of fault rock nomenclature, which are largely genetic in nature.
Hoehn, Jack R., "Low-Temperature Deformation of Mixed Siliciclastic & Carbonate Fault Rocks of the Copper Creek, Hunter Valley, and McConnell Thrusts" (2014). Honors Papers. 293.