HR: 0800h
AN: T31A-0277    [Abstracts]
TI: Geometrical analysis of the structure in the western flank of the Chilean Andes at 34°15'S-34°30'S
AU: * JARA, P P
EM: pajara@ing.uchile.cl
AF: UNIVERSIDAD DE CHILE, DEPARTMENT OF GEOLOGY, PLAZA ERCILLA 803, SANTIAGO, 21, Chile
AU: CHARRIER, R
EM: rcharrie@cec.uchile.cl
AF: UNIVERSIDAD DE CHILE, DEPARTMENT OF GEOLOGY, PLAZA ERCILLA 803, SANTIAGO, 21, Chile
AU: ARRIAGADA, C
EM: cearriag@ing.uchile.cl
AF: UNIVERSIDAD DE CHILE, DEPARTMENT OF GEOLOGY, PLAZA ERCILLA 803, SANTIAGO, 21, Chile
AU: FARIAS, M
EM: mfarias@dgf.uchile.cl
AF: UNIVERSIDAD DE CHILE, DEPARTMENT OF GEOLOGY, PLAZA ERCILLA 803, SANTIAGO, 21, Chile
AB: We present a structural analysis of strongly deformed Cenozoic volcanic rocks of the western Principal Cordillera between 34°15'S and 34°30'S. Deformation has been related to the inversion of the Abanico Basin occurred between 22 and 16 Ma. The structural array is characterized by a syncline with a very steep western limb and a rather flat slightly folded axial zone. On both sides of this structure, layers dip in directions opposite to the syncline flanks, suggesting disruption of anticlines by faulting. The reconstructed geometry performed on 6 cross- sections indicates that: 1. Deformation occurred by "fault-propagation folding" with considerable fault displacement, and 2. The anticlines were transported by the faults cutting their crests along the axial plane, similar to the anticlinal breakthrough deformation modes. Based on this mechanism and the relations between the axial and cut off angles, we developed a kinematic model using geometric methods and the Trishear program. Results suggests that folding was controlled by two E-vergent faults (western, WF, and eastern, EF). The most important (WF) would have a cutoff angle 40°-60°, which is compatible with inverted normal faults. Indeed, the regional nature of shortening in this region has been interpreted as the result of basin inversion. The EF has a cutoff angle of about 20 degrees, which is compatible with a neoformed thrust and allowing its interpretation as a short cut. These structures have accommodated ca. 30% (2 to 3 km) of shortening in this region. Although our proposition at depth for the main fault geometry is based on the surface analysis, it is quite consistent with the structural array interpreted by seismicity and MT images. Moreover, this structure seems to be the upward prolongation of a W-dipping ramp structure, connecting the subduction zone with the tectonic front of the mountain belt, in a zone where the ramp flattens and forms a detachment at 15-20 km depth beneath the western edge of the Principal Cordillera.
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8104 Continental margins: convergent
DE: 8108 Continental tectonics: compressional
SC: Tectonophysics [T]
MN: 2007 Fall Meeting