HR: 10:55h
AN: U52A-03    [Abstracts]
TI: Oroclinal Bending and Mountain Uplift in the Central Andes
AU: Mpodozis, C
EM: cmpodozis@sipetrol.cl
AF: Sipetrol S.A., Vitacura, Santiago, Chile
AU: * Arriagada, C
EM: cearriag@cec.uchile.cl
AF: Dpto. Geologia, Universidad de Chile, PLaza Ercilla 803, Santiago, Chile
AU: Roperch, P
EM: pierrick.roperch@ird.fr
AF: IRD UR154-LMTG & Geosciences Rennes, Campus de Beaulieu, Rennes, 35042, France
AB: The large paleomagnetic database now available for the Central Andes permits a good understanding of the overall spatial and temporal variations of rotations. Mesozoic to Early Paleogene rocks along the forearc of northern Chile (23°-28°S) record significant clockwise rotations (>25°) [Arriagada et al., 2006, Tectonics, doi:10.1029/2005TC001923]. Along the forearc of southern Peru, counterclockwise rotations recorded within flat lying red-beds (Moquegua Formation) increase from about -30° at 17.5°S to - 45° at15.5°S and decrease through time from the late Eocene to the late Oligocene-early Miocene [Roperch et al., 2006, Tectonics, doi:10.1029/2005TC001882]. Recently published thermo-chronological studies show evidence for strong exhumation within Bolivian Eastern Cordillera and the Puna plateau starting in the Eocene while structural studies indicate that the majority of crustal shortening in the Eastern Cordillera occurred during the Eocene-Oligocene, although the final stages of deformation may have continued through the Early Miocene. Rotations in the Peruvian and north Chilean forearc thus occurred at the same time than deformation and exhumation/uplift within the Eastern Cordillera. In contrast Neogene forearc rocks in southern Peru and northern Chile do not show evidences of rotation but low magnitude (10°) counterclockwise rotations are usually found in mid to late Miocene rocks from the northern Altiplano. These Neogene rotations are concomitant with shortening in the Sub-Andean zone and sinistral strike-slip faulting along the eastern edge of the northern Altiplano. We interpret the rotation pattern along the southern Peru and north Chile forearc as a result of strong late Eocene- late Oligocene oroclinal bending of the Central Andes associated with shortening gradients along the Eastern Cordillera associated both with the Abancay deflection and the Arica bend. The amount and spatial distribution of pre-Neogene shortening needed to account for oroclinal bending is difficult to estimate as the rotations may be partly driven by transpression along strike slip shear zones. The large rotations strongly highlight the importance of the pre-Neogene tectonic history in the evolution of the Central Andes.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 1527 Paleomagnetism applied to geologic processes
DE: 8000 STRUCTURAL GEOLOGY
DE: 8108 Continental tectonics: compressional
SC: Union [U]
MN: 2007 Joint Assembly