Separating Regional and Local Components of Uplift in the Western Transverse Ranges of California to Test Models of Mountain Belt Formation

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The origin and development of mountain belts has long been of special interest to people and a primary target of research in the Earth Sciences. This study will advance our scientific understanding of the processes that control the uplift of mountains by studying the patterns and rates of elevation change in an actively-growing mountain belt. The western Transverse Ranges of California are being uplifted by compression along the boundary between the North American and Pacific tectonic plates. In addition to the uplift of individual mountain ranges along specific faults, the lower valley areas are also rising, indicating a deeper cause to the regional uplift of the mountains. Old floodplains that have been lifted above their rivers by tectonic forces will be used as reference markers to measure the amount and rate of tectonic uplift and investigate how local vs. regional mechanisms contribute to mountain growth. The scientific advances associated with this project are coupled with training and education of both graduate and undergraduate students at a Hispanic Serving Institution that emphasizes inclusion of underrepresented groups in Science, Technology, Engineering, and Mathematics (STEM) fields. The project will also benefit the local population of southern California through enhancing understanding of regional seismic hazards posed by the faults that bound and underlie the western Transverse Ranges. Regional uplift affects an entire mountain belt, whereas local uplift results in the production of relief in the form of individual ranges and valleys. The western Transverse Ranges (WTR) of California are an active fold and thrust belt where high rates of shortening have been interpreted from geodetic studies and from geologic reconstructions. Uplift rates based on marine terraces and river terraces along the southern coast of the WTR are as high as 7 millimeters per year but vary dramatically along the coast across faults and folds that trend oblique to the coast. These high uplift rates, as measured in the elevated hanging walls of reverse faults or actively growing anticlines, are local uplift rates that are most likely not characteristic of the entire mountain belt. This project will develop a more complete picture of topographic development in the WTR by using previously unstudied fluvial strath terraces present within the WTR, and marine terraces along the western coast, as markers for vertical deformation across the mountain belt. The terraces have been offset and lifted in the hangingwalls of reverse faults, but their presence in the footwall valleys as well indicate an additional component of regional uplift that must be occurring on deeper structures. Thus, it is possible to measure both local and regional uplift and separate the two components. Luminescence and radiocarbon dating will be used to establish a Late Quaternary chronology of the terraces to calculate the timing and rate of deformation and topographic development.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.