HR: 15:45h
AN: GP23A-08    [Abstracts]
TI: Tectonic Rotations in the Southern Central Andes
AU: * Arriagada, C
EM: cearriag@cec.uchile.cl
AF: Departamento de Geologia, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile
AU: Mpodozis, C
EM: cmpodozis@sipetrol.cl
AF: Sipetrol S.A., Vitacura, Santiago, Chile
AU: Roperch, P
EM: pierrick.roperch@ird.fr
AF: IRD UR154-LMTG & Geosciences Rennes, Campus de Beaulieu, Rennes, 35042, France
AB: During the last ten years numerous paleomagnetic studies have reported large clockwise rotations (>25°) in Mesozoic and early Paleogene rocks along the forearc of northern Chile (Arriagada et al., 2003, doi:10.1029/2001JB001598; Arriagada et al., 2006, doi:10.1029/2005TC001923; Taylor et al., 2007, doi:10.1029/2005JB003950). Taylor et al (2007) have argued that these rotations occurred in response to rapid and highly oblique Nazca-South American plate convergence between 60-45 Ma, prior to later Incaic deformation mostly localized along the Domeyko fault system (DFS). However, the striking symmetry of the pattern of clockwise rotations in northern Chile and counterclockwise rotations in southern Peru (Roperch et al., 2006, doi:10.1029/2005TC001882) suggests that rotations likely occurred contemporaneously with the rotations in Peru and pre 20 Ma compressional deformation in the Bolivian Eastern Cordillera. Thus the rotations within the Chilean forearc appear to be not only the result of transpression associated to oblique convergence west of the DFS but also to deformation that should have occurred across the Puna region during the late Eocene - Oligocene. To test this hypothesis, we drilled 31 sites in late Paleozoic and Tertiary (pre Miocene) red beds in the southern Puna. Characteristic remanent magnetizations were determined after detailed thermal demagnetization. Preliminary results show a regional pattern of highly variable clockwise rotations. Measurements of anisotropy of magnetic susceptibility show that most sites record a well-defined magnetic lineation oriented either NS or NNE- SSW that we interpret as evidence for the record of Andean compression even at sites far away from major thrust faults. The deviation of the AMS lineation from a NS trend can be correlated with the tectonic rotation determined by the characteristic remanent magnetizations.
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: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly