HR: 1340h
AN: T53A-0475    [Abstracts]
TI: Extensional Basins in a Convergent Margin: Oligocene-Early Miocene Salar de Atacama and Calama basins, Central Andes
AU: * Jordan, T E
EM: tej1@cornell.edu
AF: Dept. Earth and Atmospheric Sciences, Cornell Univ., Snee Hall, Ithaca, NY 14853-1504 United States
AU: Mpodozis, C
AF: SIPETROL, Vitacura 2736, Piso 8 Las Condes, Santiago, 0000 Chile
AU: Blanco, N
AF: SERNAGEOMIN, Casilla 10465, Santiago, 0000 Chile
AU: Pananont, P
AF: Physics, Faculty of Sciences, Mahidol Univ., Rama 6 Road, Rajthevee, Bangkok, 10400 Thailand
AU: D vila, F
AF: Dept. Earth and Atmospheric Sciences, Cornell Univ., Snee Hall, Ithaca, NY 14853-1504 United States
AB: The Salar de Atacama Basin (SdAB) is the largest and most persistent sedimentary basin of northern Chile, accumulating nonmarine sediment from Cretaceous to modern times. Its northwestern neighbor, the Calama, was a Cenozoic basin. Although SdAB was in the backarc zone early in the Andean orogeny, both are now forearc basins. Others demonstrated that the basins overlie anomalously cold, strong, and dense crust and lithosphere. We focus on an extensional Oligocene basin stage. Interpretation of the basin-controlling faults is based on seismic reflection studies supported by field relations. The SdAB is limited to the west by the NNE-trending, steeply east-dipping, Paciencia Fault (PF). The PF experienced 5-7 km of down-to-the-east offset during the Oligocene-early Miocene. Syntectonic strata, an arid succession of siliciclastics and evaporites, are asymmetric, with thicknesses of 5000 m and abundant halite adjacent to the PF, and of 1000 m with fine detrital clastic strata 25 km farther east. Relations in conglomeratic growth strata that overlap the PF also demonstrate normal displacement during sediment accumulation. Seismic data reveal that a buried normal fault with 1-1.5 km down-to-the-east displacement limits the western margin of the Oligocene-Miocene Calama siliciclastic basin fill. Regionally, Oligocene-early Miocene margin-parallel strike-slip deformation dominated northwest of the basins, contributing sinistral offset (West Fissure Fault) to the northern segment of the long-lived Domeyko Fault System. The new SdAB and Calama data reveal that a 20,000 km2 domain of extensional basins existed within the dominantly strike-slip region. Even if PF and the fault in the Calama Basin were transtensional, the proportion of extension to strike-slip displacement is much greater in these basins than elsewhere in northern Chile. Further study is required to understand what combination of factors caused this kinematic distinction as well as delayed the onset of CVZ volcanism in the same area.
DE: 9360 South America
DE: 8015 Local crustal structure
DE: 8102 Continental contractional orogenic belts
DE: 8105 Continental margins and sedimentary basins
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting