Continental Deformation: New Tools and New Constraints on Convergent and Collisional Tectonic Systems from the Greater Caucasus

The distribution of strain in continents is of primary importance in determining Earth's topography, the distribution of Earth resources, and hazards. This dissertation explores several records of continental deformation on timescales from thousands to millions of years and spatial scales from single faults to whole orogens. Many of these records are influenced by a complex set of factors and have limited sampling, so I develop and use new Bayesian statistical approaches in order to rigorously quantify uncertainties in data and interpretations. The dissertation work is broadly centered on three themes. First, a novel Bayesian statistical method for modeling and comparing detrital zircon U-Pb age distributions is developed (Chapters 2, 3). It is shown that this method can be used to accurately infer uncertainties on population age distributions inferred from samples, leading to more robust interpretations of geologic processes from detrital geochronology datasets. In addition, the new method is shown to permit robust quantitative inferences of mixing and dilution between detrital zircon populations. Second, the potential to infer paleoseismic slip histories from bedrock fault scarp rock properties including strength and roughness is explored using bedrock scarps of the Hebgen Fault, Montana, and the Pleasant Valley Fault, Nevada (Chapters 4, 5). It is demonstrated that on bedrock normal fault scarps, Schmidt hammer strength measurements and microtopographic roughness are distributed in a stepwise pattern up-scarp, suggesting that these physical properties reflect exposure of patches of the scarp during successive earthquakes. The number and timing of paleoseismic events inferred from bedrock scarp strength and microtopography are consistent with available independent constraints on paleoseismic slip history for the analyzed scarps. Third, the structural and stratigraphic effects of the transition from subduction to continental collision are investigated using the Greater Caucasus as a natural laboratory (Chapters 6, 7). A structural and thermochronometric investigation of the Eastern Greater Caucasus, where subduction is active, reveals that pervasive out-of-sequence folding in the core of the range plays a significant role in thickening the accretionary wedge as it grows in order to maintain a critical taper. Detrital zircon provenance of three foreland basin stratigraphic sections distributed along strike of the orogen reveals a detailed picture of the changes in source exposure and sediment routing that accompany the transition from subduction to collision. Initial entrance of tapered lower plate continental lithosphere into the subduction zone occurred between 15 and 8 Ma in the Caucasus, 3 - 10 Myrs before plate kinematic and exhumational effects of collision began at 5 Ma. Inferred collision-related slowing of plate convergence and acceleration of exhumation in the Caucasus coincided with the development of erosive conditions in the foreland basin between the two colliding continents and the concomitant formation of an axial drainage network that transported sediment laterally within the foreland basin. The chapters of the dissertation are unified in their exploration of how continental deformation at different temporal and spatial scales is preserved in the geologic record. Because of the complexity of many of these records and the uncertainties inherent in their interpretation, Bayesian statistical methods offer a promising way to increase the reliability of quantitative geological interpretations, as documented in several of the chapters. In addition, the dissertation makes a significant contribution to our understanding of the transition from subduction to collision.PHDEarth and Environmental SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/153393/1/alextye_1.pd