Abstract
Bedrock (U-Th)/He data reveal an Eocene exhumation difference greater than four kilometers athwart Owens Valley, California near the Alabama Hills. This difference is localized at the eastern fault-bound edge of the valley between the Owens Valley Fault and the Inyo-White Mountains Fault. Time-temperature modeling of published data reveal a major phase of tectonic activity from 55 to 50 Ma that was of a magnitude equivalent to the total modern bedrock relief of Owens Valley. Exhumation was likely accommodated by one or both of the Owens Valley and Inyo-White Mountains faults, requiring an Eocene structural origin of Owens Valley 30 to 40 million years earlier than previously estimated. This analysis highlights the importance of constraining the initial and boundary conditions of geologic models and exemplifies that this task becomes increasingly difficult deeper in geologic time.
Highlights
The accuracy of initial and boundary conditions is critical to the development of realistic models of geologic systems
A time–temperature analysis of data from Owens Valley, California leads to insights into the Cenozoic geologic evolution of the southern United States (U.S.) Cordillera, placing new constraints on the timing and mechanism of the demise of the Nevadaplano [5]. (U-Th)/He data from several published transects across Owens Valley document a major Eocene exhumation difference between the bedrock to the east and west of the valley (Figure 1)
In shifting the initial and boundary conditions for the regional late Cenozoic tectonic evolution of Owens Valley, this new analysis requires that contiguity of the Nevadaplano with the southern Sierra Nevada did not persist past circa 50 Ma, roughly 30 to 40 million years earlier than previous estimates [6,7,8]
Summary
The accuracy of initial and boundary conditions is critical to the development of realistic models of geologic systems. Features can develop under one tectono-climatic regime and persist on geologic time scales, often controlling later geologic evolution by imposing initial and boundary conditions through mechanisms such as the structural reactivation of faults and geomorphic inheritance of landscapes (e.g., [1,2]). Identifying such paleo-features is a prerequisite to the optimization of models of geologic processes and assessing the assumptions that underly them. In shifting the initial and boundary conditions for the regional late Cenozoic tectonic evolution of Owens Valley, this new analysis requires that contiguity of the Nevadaplano with the southern Sierra Nevada did not persist past circa 50 Ma, roughly 30 to 40 million years earlier than previous estimates [6,7,8]
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