HR: 10:20h
AN: U52A-01    [Abstracts]
TI: The Southern Central Andes at 25.5šSL: a Non-Balanced Crustal Cross-Section
AU: Muñoz, J
EM: jamuñoz@ub.edu
AF: Departament de Geodinàmica i Geofísica, Facultat de Geologia, Universitat de Barcelona, Martí i Franques s/n, Barcelona, 08028, Spain
AU: * Amilibia, A J
EM: aamilibiac@ub.edu
AF: Departament de Geodinàmica i Geofísica, Facultat de Geologia, Universitat de Barcelona, Martí i Franques s/n, Barcelona, 08028, Spain
AU: Carrera, N
EM: nuriacarrera@ub.edu
AF: Departament de Geodinàmica i Geofísica, Facultat de Geologia, Universitat de Barcelona, Martí i Franques s/n, Barcelona, 08028, Spain
AU: Roca, E
EM: eduardroca@ub.edu
AF: Departament de Geodinàmica i Geofísica, Facultat de Geologia, Universitat de Barcelona, Martí i Franques s/n, Barcelona, 08028, Spain
AU: Sàbat, F
EM: sabat@ub.edu
AF: Departament de Geodinàmica i Geofísica, Facultat de Geologia, Universitat de Barcelona, Martí i Franques s/n, Barcelona, 08028, Spain
AU: Mon, R
EM: decano@csnat.unt.edu.ar
AF: Departamento de Geología, Facultad de Ciencias Naturales e Instituto Miguel Lillo, Universidad de Tucumán, Miguel Lillo 205, Tucumán, 4000, Argentina
AU: Chong, G
EM: gchong@ucn.cl
AF: Departamento de Ciencias Geológicas, Facultad de Ingeniería y Ciencias Geológicas Universidad Católica del Norte , Av. Angamos 0610, Antofagasta, Chile
AB: The Andes is the type orogen for subduction contractional systems but many uncertainties still exist about the crustal structure and few complete cross-sections have been done and published. Estimates of shortening have been in the past years a matter of debate mainly as far as the deficit of tectonic shortening to account for the known crustal thickness is concerned. Estimates for this shortening have mainly relied on shortening calculations made on cross-sections of parts of the orogen. It is known that along strike motion of material do occur in most mountain belts and has to be taken into account in any precise orogenic mass balance. It has also recently argued that the shortening deficit in the Andes results from plane strain calculations not considering the out of plane section motion of material. However, 2D estimates of shortening on cross-section balancing are still a first valid approximation to a mass balance and construction of cross-sections across the entire Andean orogen is a priority. A complete cross-section of the Central Andes at 25.5° S has been constructed based mostly on surface geological data. This work has involved field mapping and interpretation of aerial and satellite images across all the main structural units at this Andean transect. Structural data have been acquired all along the cross-section. Interpretation of seismic reflection profiles has also integrated where available, mostly in the eastern part of the cross-section. Published geophysical data have used to constrain the deep crustal structure. Along this cross-section, crustal mass balance and shortening estimates along the non-thinned South America crust shows that shortening based on the flexural-slip restoration of the bottom of syn-compressive rocks (bottom of the Cenozoic in Argentina and of the Cretaceous in Chile) is of 108 km whereas the shortening based on the South America crust area restoration, considering an initial crustal thickness of 38 km, increases to 271 km. This denotes that contractional structures only explain 39,85% of the Andean crustal thickening along the presented section, and that the remaining Andean crustal thickening (60,15%) is related to other processes. It should be noted, that this thickening non explained by the observed contractional structures is equivalent to 163 km of non- thickened South America crust and not very different to the area of the low-velocity zone observed at middle crust levels. This 163 km are also similar to the calculated amount of forearc tectonically eroded by the subducted Nazca plate.
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8104 Continental margins: convergent
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Union [U]
MN: 2007 Joint Assembly