Evolution of active fault systems and their topographies
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Ellis, Magdalena. Evolution of Active Fault Systems and Their Topographies. Chapel Hill, NC: University of North Carolina at Chapel Hill Graduate School, 2015. https://doi.org/10.17615/5yv0-tf57APA
Ellis, M. (2015). Evolution of active fault systems and their topographies. Chapel Hill, NC: University of North Carolina at Chapel Hill Graduate School. https://doi.org/10.17615/5yv0-tf57Chicago
Ellis, Magdalena. 2015. Evolution of Active Fault Systems and Their Topographies. Chapel Hill, NC: University of North Carolina at Chapel Hill Graduate School. https://doi.org/10.17615/5yv0-tf57- Last Modified
- September 22, 2022
- Creator
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Ellis, Magdalena
- Affiliation: College of Arts and Sciences, Department of Geological Sciences
- Abstract
- Tectonically active landscapes impact society by affecting the distribution of mineral and geothermal resources, controlling basin development and groundwater resources, and posing significant risk via seismic and geomorphic hazards. Yet several questions remain in understanding the coevolution of landscapes and tectonics: (a) What is the connection between topography and tectonics? (b) To what degree does the landscape reflect tectonic forcing? And (c) How do faults evolve through time and how is it reflected on the landscape? In this dissertation I investigate the evolution of active fault systems and their topographies in three chapters. In Chapter 1 I compile tectonic, topographic, climatic, and lithologic information on >40 dip-slip faults around the globe to quantify the relative contribution of each in shaping fault-driven topography. In Chapter 2 I use bedrock river profiles and hillslope analysis to examine the landscape response to the growth of crustal-scale normal faults in the Nevada Basin and Range. In Chapter 3 I use apatite (U-Th)/He thermochronometry to test the validity of contrasting fault-growth models in the Nevada Basin and Range. Below I describe each chapter in more detail. It is difficult to fully demonstrate the link between tectonics and topography in mountain belts because they are complicated tectonomorphic systems. As a result, existing data sets are often relevant at very different scales, complicating comparisons of the processes involved that shape a mountain belt. A simplifying approach is to focus on active faulting and associated emerging topography. In Chapter 1 I compile tectonic, topographic, climatic, and lithologic variables for 41 active dip-slip faults across the globe to investigate how these contributing variables are correlated. Motivated by research that uses established fault growth models to assess the landscape response to fault growth (Barnes et al., 2011; Densmore et al., 2007b), this research is the first comprehensive and global analysis of patterns of along-strike relief for dip-slip faults. One of the main motivating factors in undertaking this research was to use a space-for-time substitution to estimate the temporal scale of relief growth. If lateral fault propagation is a continuous process, and I measure the along-strike distance within which relief increases from zero at the tips, then it follows that using the rate of lateral propagation I can calculate the temporal scale of the relief limit. The assumptions inherent in this idea led to the research undertaken in Chapters 2 and 3. My results show surprising correlations and noncorrelations between topography and independent variables, leading to new ideas about the relative importance of tectonics, climate, and lithology in shaping fault-driven landscapes. In Chapter 2 I use footwall channel morphologies, hillslope analysis, landscape modeling, and existing low-temperature thermochronologic data to investigate normal fault slip histories of three footwall mountain ranges in the Nevada Basin and Range. Active mountain landscapes are a product of erosional processes driven by tectonics and modulated by climate. Channel incision sets the lower boundary condition for hillslopes and dictates the texture and relief of uplifting topography. Following a change in tectonics or climate, streams respond by adjusting their form. My results from the Pine Forest Range, the Jackson Mountains, and the Santa Rosa Range show that there is a suite of knickpoints in the channel profiles that segment the channels into upper reaches with low gradients and lower reaches with high gradients. I determine these knickpoints to be migratory, whereby they initiated at the range fronts as a response to a change in slip rate. I then use channel reconstructions, watershed volume estimates, and a knickpoint celerity model to constrain the timing and rate of knickpoint initiation and migration. My results require incision and knickpoint migration that is much younger than the thermochronology is able to constrain, suggesting renewed slip starting ~5-3 Ma. A key finding in this research is that the heights of the observed migratory channel knickpoints reside in a relatively narrow range of elevations. Because knickpoint height is theoretically controlled by fault slip rate, such a pattern indicates that the rate of slip on the range-front faults does not vary along strike, as predicted by a conventional model for fault growth. This observation does not support the assumption in Chapter 1 that fault growth follows a conventional model, whereby fault slip is a continuous process since inception and the highest displacement rate is found in the fault center. In Chapter 3 I address and test these conventional models of fault growth. In Chapter 3 I explore how apatite (U-Th)/He thermochronology (AHe) can be used to test conventional models of fault growth by application to two crustal-scale normal faults in the Nevada Basin and Range province. Faults are commonly thought to grow by simultaneously accumulating displacement and propagating laterally. There is a dearth of field observations actually documenting the lateral growth of faults, preventing testing of conventional fault growth models and thus full understanding of fault growth. Low-temperature thermochronology has never been used to quantify normal fault propagation, but has been successful in analyzing exhumation and fault slip within various tectonic settings. My results from the Pine Forest Range indicate that the studied faults did not grow by simultaneously accumulating displacement and lengthening, but rather that the fault reached its modern fault length within 3-4 m.y. of inception, ~8-10 Ma. This key finding supports the constant fault-length model of fault growth (Walsh et al., 2002) and suggests that the modern Basin and Range physiography was established by the late Miocene. The research presented in this dissertation is motivated by trying to understand (1) how faults grow and (2) how landscapes reflect fault slip. Integrating thorough geomorphic observations with thermochronologic data serves to develop a complete spatio-temporal history for fault evolution. The following chapters are presented as a series of manuscripts that stand alone for publication, but strive to address the same general motivating questions about fault-driven landscapes.
- Date of publication
- May 2015
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- Rights statement
- In Copyright
- Advisor
- Barnes, Jason B.
- Wegmann, Karl
- Coleman, Drew S.
- Stewart, Kevin
- Pavelsky, Tamlin
- Degree
- Doctor of Philosophy
- Degree granting institution
- University of North Carolina at Chapel Hill Graduate School
- Graduation year
- 2015
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- Place of publication
- Chapel Hill, NC
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- There are no restrictions to this item.
- Date uploaded
- June 25, 2015
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Ellis_unc_0153D_15280.pdf | 2019-04-12 | Public | Download | |
Appendix 2: Google Earth (.kmz) file to accompany Chapter 1 | 2019-04-12 | Public | Download |