Geologic Estimates of Northeastward Andean "Escape" for the Last 0.5 Ma
Abstract
CASA GPS measurements (Trenkamp et al., 2002) suggest that a large part of the northern Andes is "escaping" to the northeast relative to stable South America at a rate of 6±2 mm/a. The displacement rates of seven sites in Venezuela, Colombia, and Ecuador are statistically identical at the 2 sigma confidence level. This study compares this GPS rate to 19 published field geologic estimates of displacement rates, such as displaced glacial moraines and offset pyroclastic flow. Dated displacements compiled in this study were obtained from the Gulf of Guayaquil, Pallatanga, Chingual-La Sofia, and Cayambe-Afiladores-Sibundoy fault systems in Ecuador and southern Colombia and the Bocono fault system in Venezuela. Right-lateral slip estimates on the individual fault segments range from 1.4 mm/a to 9.7 mm/a. The mean estimated geologic slip rate for the last 86,000 BP is 7.6 mm/a with an R2 value of 0.97. This estimate is very similar to the GPS measurements of present day motion at the 2 sigma level. Three estimates indicate that slip rates of 4 to 6 mm/a continued back to 500,000 BP. No geologic slip estimates have been reported for Ecuador prior to that time period. The "escape" of the Northern Andes is believed to be a result of increased coupling between the obliquely subducting Nazca plate and the overriding South American plate due to the subduction of the Carnegie ridge in the Ecuador-Colombian trench. If this is correct, the slip estimates for the northern Andes suggest that the Carnegie Ridge arrived at the trench prior to 500,000 BP.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.G21A0671E
- Keywords:
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- 3040 Plate tectonics (8150;
- 8155;
- 8157;
- 8158);
- 5475 Tectonics (8149);
- 8011 Kinematics of crustal and mantle deformation;
- 8120 Dynamics of lithosphere and mantle: general (1213);
- 8150 Plate boundary: general (3040)