This research project extends deformation rate estimates for the Death Valley-Fish Lake Valley transcurrent fault system, western Great Basin, to the last 5 million years with a stepwise resolution of 100,000 and possibly 10,000 years. The work will focus on a major restraining bend in the Death Valley-Fish Lake Valley fault system that formed as lateral displacement along the Death Valley-Fish Lake Valley fault was transferred to local shortening and uplift. The primary objectives are: (1) determination of deformation rates; (2) assessment of the role of discrete versus distributed deformation mechanisms; and (3) characterization of the three-dimensional geometry and evolution of structures and possible vertical-axis rotation during formation of the restraining bend. The project involves integration of detailed geologic mapping, structural analysis, stratigraphic characterization, geochronology, and magnetostratigraphic-paleomagnetic analysis. Field and laboratory studies will define the three-dimensional geometry, tectonic evolution, and mechanisms of deformation active during the formation of this major contractional structure. Assessment of deformation rates over different time intervals utilizes a robust chronostratigraphic framework and determination of aggregate and incremental displacements from deformation models. By combining high-precision 40Ar/39Ar age data for numerous key stratigraphic intervals (e.g. specific tephra layers and volcaniclastic deposits) with a magnetic polarity stratigraphy that can be correlated with the astrochronologically-tuned Neogene geomagnetic polarity timescale, temporal resolutions of 100,000 and possibly 10,000 years will be obtained. Combining this temporal information with field relations involving synorogenic strata and three-dimensional structural models allows resolution of incremental displacements of 100 to 1,000 meters during growth of the structure. With these displacement and timing ranges, the displacement and growth of the restraining bend provides rate determinations comparable to those for late Quaternary surface displacements.
Accurate estimates of the rates of a broad range of geologic processes are critical to understanding the evolution of the Earth's surface over different time scales. The deformation of continents through the formation of faults and the release of seismic energy as earthquakes, in what is known as the earthquake cycle, is becoming better understood over durations of tens to tens of thousands of years and such information provides important insights into whether or to what degree earthquake activity remains the same through geologic time. Unfortunately, the ability to estimate deformation rates on major fault systems becomes more poorly resolved with the passage of time, mainly due to the obscuring effects of younger deformation and the inability to measure offset of well-dated marker units across faults. The capacity to estimate deformation rates over durations of tens of thousands and hundreds of thousands of years in most parts of the world remains elusive for periods of geologic time ranging from hundreds of thousands and millions of years. Enhanced understanding the earthquake cycle over durations of millions of years requires unraveling Earth's history over different time scales, and can be addressed only in rare instances where geologic structures are well preserved and provide the capacity to date geologic events with high- precision. The anticipated results of this research project will quantify the progressive development of a part of a major geologic fault system exposed within the broad, currently seismically active region that is the boundary between the eastern Sierra Nevada and the western Great Basin in the western US Cordillera. The Death Valley-Fish Lake Valley fault system has been active for several millions of years and records tens of kilometers of horizontal displacement. When compared to well determined contemporary and latest Quaternary deformation rate estimates established geodetically and from offset geomorphic features, the results of this study will help tie active tectonic to long-term deformation processes.
