Document Type
Thesis
Abstract
The Cordillera Blanca in the central Peruvian Andes displays a rich glacial and tectonic history. It is a region of active extension in the midst of a collisional tectonic setting, and contains the most extensive glacial history found anywhere in the tropics. The Cordillera Blanca detachment fault is a major west-dipping normal fault that strikes north-south along the western side of the Cordillera Blanca. In order to calculate slip rates and recurrence intervals along this fault, we conducted surveys of offset geomorphic features using a laser theodolite total station. We surveyed an offset moraine crest at Quebrada Cojup, and tectonically generated fluvial terraces at Quebrada Queroccocha. We also used GPS surveys to map moraine crests at Cojup, and fault and terrace surfaces at Querrococha. At Cojup, the survey of the fault scarp shows a vertical displacement of ~60 m, on a surface that has been dated using cosmogenic radionuclides as 20.0 + 1.7 ka. The average vertical offset rate revealed here is ~3 mm/yr. Differentially corrected GPS files allowed us to construct a map of moraine crests along the south side of Cojup, showing at least 4-5 crests of different ages. At Querrococha, we surveyed a sequence of 6 terraces observed only on the footwall side of the fault, that records 5 tectonic events since moraine deposition. Based upon profiles constructed along the strike of the valley and cross-sections running perpendicular to this, spacing between each of these terraces has been estimated as ~2.7 m. This represents the amount of offset generated during each tectonic event. By measuring concentrations of the cosmogenic radionuclide 'Be, the fourth oldest terrace, T4, has been dated at 13.6 + 1.3 ka. The vertical offset rate for the past ~13.6 ka ranges from 0.57 to 0.76 mm/yr, and the recurrence interval for the 3 events which occurred in that time ranges from 3400 to 4500 years.
Date Awarded
2000
Department
Geology
Advisor 1
Gregory S. Hancock
Advisor 2
Christopher M. Bailey
Recommended Citation
DeSmedt, Megan, "Determining uplift ad extension rates along the Cordillera Blanca Detachment Fault of the Central Peruvian Andes" (2000). Geology Senior Theses. William & Mary. Paper 62.
https://scholarworks.wm.edu/geologyseniors/62
