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Young displacements on the Atacama Fault System, northern Chile from field observations and cosmogenic 21 Ne concentrations
Author(s) -
González L. Gabriel,
Dunai Tibor,
Carrizo Daniel,
Allmendinger Richard
Publication year - 2006
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/2005tc001846
Subject(s) - fault scarp , geology , alluvial fan , fault (geology) , alluvium , pleistocene , quaternary , fault trace , seismology , geomorphology , slip (aerodynamics) , paleontology , structural basin , physics , thermodynamics
We present the first numerical age constraint for young deformation of the Atacama Fault System (AFS) in northern Chile. The young activity of the AFS is expressed by several fault scarps which affects alluvial fan sediments of the eastern side of the Coastal Cordillera (23°30′–23°42′S). Detailed mapping of alluvial fans reveals a complex relationship between fault motion, erosion and alluvial fan development. An older group of alluvial fans became inactive prior to the scarp formation. Younger alluvial fans, arising directly from feeder channels and entrenched in the fault scarps, posts date the scarp formation. The youngest slip on the AFS is recorded by headward eroding channels entrenched across the scarp which are in turn displaced vertically 0.3–0.5 m by the fault. Quartz fragments in four sites on the older inactive fan group were analyzed for cosmogenic 21 Ne concentrations yielding an average age of 424 ± 151 ka, the upper limit for the recent activity of the fault. Combined with the height of fault scarp, we calculate a 0.01 mm/yr minimum vertical fault slip rate. Thus young displacement on the AFS is Quaternary in age and confined to the late Pleistocene.