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Neotectonics of the Cordillera Blanca, Peru
Gallagher, Stephen B.
Gallagher, Stephen B.
Abstract
The Cordillera Blanca, Peru, have an extensive tectonic and glacial history. One of the most striking features is the Cordillera Blanca Fault Zone, which is a north-south striking west-dipping normal fault. This fault zone has become the focus of much debate since it has developed in a compressional setting. To calculate slip rates along the fault, surveys were conducted at two locations; Quebrada Tuco, in the south and Quebrada Huaytapallana in the north. The fault scarp at Quebrada Tuco offset a valley floor created by a glacier during the last glacial maxima ~17,500 years B.P. The surveys yielded an average vertical offset of 14 m giving an offset rate of 0.8 mm/yr. The fault scarp surveyed at Quebrada Huaytapallana offset a lateral moraine. This moraine was dated at ~19,000 years B.P. via cosmogenic radionuclides. The offset at Quebrada Huaytapallana was determined to be 52m with an offset rate of 2.7 mm/yr. Besides tectonic forcing, isostatic compensation is a factor in topographic production. Calculations of the effects of isostasy include change in peak elevation and the percentage of uplift due to isostatic compensation. The change in peak elevation was calculated to be ~1.2 km and calculations show that isostasy accounts for between 13 and 30% of the total uplift rates.
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2001-01-01
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Geology