HR: 17:15h
AN: T32E-06    [PDF]
TI: Late Cenozoic tectonics of the Coastal Cordillera of N Chile and implications for paleoclimate and interplate processes
AU: * Allmendinger, R W
EM: rwa1@cornell.edu
AF: Cornell University, Earth \& Atmospheric Sci., Ithaca, NY 14853-1504 United States
AU: Gonz\'{a}lez, G
EM: ggonzale@ucn.cl
AF: Universidad Cat\'{o}lica del Norte, Dpto. Ciencias Geol\'{o}gicas, Antofagasta, 1000 Chile
AU: Yu, J
EM: yuie@gps.caltech.edu
AF: Cornell University, Earth \& Atmospheric Sci., Ithaca, NY 14853-1504 United States
AU: Isacks, B
EM: bli1@cornell.edu
AF: Cornell University, Earth \& Atmospheric Sci., Ithaca, NY 14853-1504 United States
AU: Hoke, G
EM: gdh7@cornell.edu
AF: Cornell University, Earth \& Atmospheric Sci., Ithaca, NY 14853-1504 United States
AB: The Coastal Cordillera of northern Chile is located in the hyperarid Atacama Desert and is situated over the interplate seismic zone of the Nazca-South America convergent plate boundary. The Coastal Cordillera is bounded to the west by a 1000 m high escarpment that plunges directly to the sea north of Iquique but to the south has a 1-5 km wide Pleistocene abrasion platform at its base. We use a 20 m InSAR digital elevation model (DEM) combined with fieldwork to investigate the relations between the late Cenozoic tectonics and drainage development in the Cordillera between the R\'{i}o Loa (21.6S) and the Quebrada de Camarones (19S). Late Cenozoic structures in this region consist of ~EW striking reverse faults and ~NS striking normal faults. The primary development of the reverse faults occurred in the Miocene and early Pliocene, though warped Pleistocene marine terraces indicate some later reactivation. These structures produce about 1% shortening parallel to, and appear to be related to the seaward concave curvature of, the plate boundary. Late Miocene to Recent normal faults throughout the Coastal Cordillera parallel the plate boundary and dip both towards and away from the trench. At several places in the study area, paleodrainages were incised across the uplifting ~EW reverse fault blocks prior to being dammed, producing internally drained evaporite basins in the footwalls of the structures. These relations indicate that there was considerably more water in the Coastal Cordillera in the latest Miocene and early Pliocene than is available at present, in agreement with the prior suggestion that the onset of hyperaridity in the region post-dates ~5 Ma. The R\'{i}o Loa, the only river to reach the sea along more than 500 km of coastline, truncates on of these paleodrainages indicating that the Loa was incised at its current location after the middle Miocene. The incision of the R¡o Loa could be due either to uplift of the Coastal Cordillera, or due to lateral (W to E) migration of its baselevel were it debouches into the ocean as the Coastal Escarpment retreats from W to E. These two processes of incision are probably controlled by underplating and subduction erosion, respectively.
DE: 1824 Geomorphology (1625)
DE: 8010 Fractures and faults
DE: 8105 Continental margins and sedimentary basins
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting