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Trench-parallel shortening in the Northern Chilean Forearc: Tectonic and climatic implications

Richard W. Allmendinger^,1, Gabriel González², Jennifer Yu³, Greg Hoke³ and Bryan Isacks³

¹ Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York 91125, USA
² Dipartamento de Ciencias Geológicas, Universidad Católica del Norte, Antofagasta, Chile
³ Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York 91125, USA

In the Central Andes, the frictional coupling between South America and the subducting Nazca Plate occurs beneath the Coastal Cordillera of northern Chile. One of the most distinctive characteristics of the Coastal Cordillera is a suite of EW topographic scarps located between 19° and 21.6°S latitude. These scarps are associated with predominantly south dipping reverse faults that have almost pure dip slip and produce shortening parallel to the plate boundary. Limited geochronology as well as more regional studies indicate that the scarps formed during the late Miocene and early Pliocene, though some show activity extending into the Quaternary. In several areas, the scarps dammed local drainages, producing internally drained basins that accumulated evaporites. This relationship indicates that the Coastal Cordillera was probably moister during the Late Miocene and Pliocene than it is today and also indicates that the Coastal Cordillera has been significantly uplifted or that the Coastal Escarpment of northern Chile has advanced significantly eastward since the Pliocene. The limited latitudinal extent of the EW scarps and their location symmetrically about the axis of topographic and Wadati-Benioff zone symmetry suggest that they owe their origin to the concave seaward shape of the continental margin due to prior formation of the Bolivian orocline.

Key Words: forearc • Andes • Chile • deformation • geomorphology • tectonics

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