Tracking the topographic evolution of the Sierra Nevada, California

Theme: Solid Earth Dynamics

Primary Supervisor:

Frances Cooper

Earth Sciences, UCL

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Secondary Supervisor:

Byron A. Adams

Earth Sciences, UCL

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Additional Supervisor(s):
Simon Tapster (British Geological Survey)
Vali Memeti (California State University, Fullerton, USA)

Project Description:

The Sierra Nevada mountains in California comprise an enormous granitic batholith created in the late Cretaceous during subduction of the Farallon Plate beneath North America. Forming part of the North American Cordillera, they stretch for 600 km and increase in elevation continuously from north to south, reaching peaks of >4,000 m. However, the reason for this variation in elevation, and when it evolved, is unclear (e.g. Wakabayashi, 2013; Clark et al., 2005). It is thought that the range originally had a consistent peak elevation of ~1500 m (Clark et al., 2005), but subsequent differential uplift and erosion created the more complex landscape seen today. This project will place new constraints on the topographic evolution of the Sierra Nevada by combining a new calibration of the aluminium-in-hornblende barometer (Mutch et al., 2018) with U-Pb zircon geochronology, geomorphology, and geospatial analysis. These elements will be integrated to derive new insights into the controls on topographic evolution.

The primary aim of the project is to determine the topographic history of the Sierra Nevada from Cretaceous emplacement of the Sierra Nevada batholith until the formation of an extensive, preserved Eocene erosional surface. The research will include fieldwork to collect samples for barometry and geochronology, laboratory analyses, and geospatial analysis. There are three main objectives:

1: Constrain emplacement depths and ages of granitic intrusions across the Sierra Nevada through aluminium-in-hornblende barometry and U-Pb zircon geochronology of key samples collected in the field.

2: Map the Eocene relict landscape of the western Sierra Nevada through quantitative topographic analysis using ArcGIS and Matlab.

3: Determine the Cretaceous–Eocene topographic history of the Sierra Nevada by combining the outputs of objectives 1 and 2, and test existing hypotheses for the evolution of the range.

Policy Impact of Research:

The topographic evolution of a mountain range results from the interplay of both tectonics (pushing them up) and climate (rain and snow eroding them down) over geologic time. Therefore, gaining a better understanding of how the Sierras have evolved will provide important information about the relative importance of tectonics and climate during their lifespan and the feedbacks between the two.

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