Rise and Fall: The Impacts of Fluctuating Lake Levels on Extensional Tectonics

Abstract:

Climate driven processes; weathering, erosion, sediment transport, and deposition, have been shown to impact the stress state and deformation along active orogens (Koons, 1989; Molnar and England, 1990; Avouac and Burov, 1996; Willett, 1999). The overall effect of climate on extensional processes is however limited to a few studies (Burov and Cloething, 1997; Burov and Poliakov, 2001; Bialas and Buck, 2009; Andrés-Martínez et al., 2019). Here we utilize a thermomechanical extensional model to investigate the potential impacts on faulting and extension due to lake loading and changes in lake levels driven by climate change. A series of simulations was carried out that varied erosion rate and maximum lake levels over a 6 Ma period of continental extension. Fault analyses focusing on heave, throw, and magnitude of dip were performed on each model. Preliminary simulations resulted in the development of graben-like structures with most of the strain accumulation occurring along a single bounding fault. Our fault analysis indicates a positive correlation between increases in maximum lake level and erosion rate and magnitude of dip along this major fault. However, a general decrease in heave/throw values suggests that strain is being shifted to other locations within and surrounding the extensional basin. Three intra- and inter-basin faults within 20 km of the bounding fault show significant increases in heave/throw values suggesting that strain was transferred to them. These preliminary results indicate that fluctuations in response to changes in climate may impact the lithospheric stress state by changing both fault geometry and morphology within the extensional basin, displacing strain away from the major bounding fault. Furthermore, observed increases in thinning factor β indicate that extension is affected, albeit subtly, by both increasing lake level and erosion rates.