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The AAPG/Datapages Combined Publications Database
AAPG Special Volumes
Abstract
2004. The American Association of Petroleum Geologists. All rights reserved.
The Andean Thrust System
Latitudinal Variations in
Structural
Styles and Orogenic Shortening
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Victor A. Ramos,1 Tom
s Zapata,2 Ernesto Cristallini,3 Antonio Introcaso4
1Laboratorio de Tectnica Andina, Departamento de Ciencias Geol
gicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina
2REPSOL-YPF S.A., Exploracon y Desarrollo en Faja Plegada, Buenos Aires, Argentina
3Laboratorio de Tectnica Andina, Departamento de Ciencias Geol
gicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina; CONICET Consejo Nacional de Investigaciones Cientificas y T
cnicas
4Instituto de Fsica de Rosario, Universidad Nacional de Rosario, Rosario, Argentina; CONICET Consejo Nacional de Investigaciones Cientificas y T
cnicas
ACKNOWLEDGMENTS
The authors are indebted to several colleagues of the Laboratorio de Tectnica Andina of the Universidad de Buenos Aires, as well as to YPF S.A. for logistic support. The SECYT PICT 06729 and CONICET PIP 4162 financed this work. The authors want to express their gratitude to reviewers Richard Allmendinger, Raymond Price, and Jorge Skarmeta for their comments and suggestions.
ABSTRACT
The different segments of the Andean thrust system have distinctive topography and inferred crustal roots. These two characteristics both depend upon crustal shortening, and on this basis they provide independent constraints for evaluating estimates of Cenozoic shortening obtained by balanced structural
cross
-
sections
of different segments of the fold-and-thrust systems. Three transects in the Central Andes are analyzed: a northern (22–23
S), a central (32–33
S), and a southern segment (37–39
S). Each segment shows different amounts of orogenic shortening, generated through a complex combination of thin- and thick-skinned thrusting. Based on known age constraints, different shortening rates are calculated for each segment. Estimates of crustal shortening derived from gravity and seismic-refraction data are used to evaluate interpretations of the
structural
style. In some segments, where alternative styles were proposed, the crustal-shortening estimates are used to identify the more realistic models.
Crustal shortening, shortening rates, and the resulting topography decrease progressively from north to south. These variations cannot be fully explained by differential fore-arc rotation, as in the Bolivian orocline model. Instead, a close correlation is suggested between the age of oceanic crust being subducted and the amount of shortening and propagation of the orogenic front toward the foreland. This fact becomes more important than fore-arc rotation farther south of the Bolivian orocline. On this basis, the present topography of the Andes, along the Nazca plate boundary, can be correlated with the age of adjacent oceanic crust.
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