The link between forearc tectonics and pliocene-quaternary deformation of the Coastal Cordillera, northern Chile

Pliocene-Quatemary tectonic extension has controlled the structural evolution of the outer forearc of northern Chile. Extensional deformation is documented by large-scale, mostly N-S-striking normal faults and open cracks that run along the forearc. The faults dip to the east and define half-graben geometries across the Coastal Cordillera (20degrees45'-23degrees30'S). Progressive trenchward tilting of the hangingwalls has produced internal unconformities within the graben and half-graben fill. This suggests that extension has been episodic, at least since the Pliocene. Northwest-striking dextral strike-slip faults occur in the northern part of the extensional fault zone of the Coastal Cordillera (20degrees40'S-21degreesl0'S), where they link N-S normal faults. Hectometric open cracks occur throughout the Coastal Cordillera, some of which are spatially associated with the normal faults. Normal and dextral faults appear to accommodate long-term extensional strain, whereas open cracks are interpreted as tensile fractures formed by either concomitant normal faulting or coseismic extension. The long-term extensional regime may result from buckle folding of the margin, which in turn produces progressive uplift of the coastal area by oceanic plate subduction, followed by continental margin collapse toward the trench. (C) 2003 Elsevier Ltd. All rights reserved.