Structural evolution of the Andes between 33°30´ and 33°45’ S, above the transition zone between the flat and normal subduction segment, Argentina and Chile.

GIAMBIAGI, L. Y RAMOS, V.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

Elsevier

Año: 2002 p. 99 - 114

0895-9811

The sector of the Andes studied in this paper (33º30´ - 33º45´ S) constitutes a key area to analyze the relationship between tectonic setting and deformation history of a transitional zone between flat (north of 33° S) and normal subduction segments (south of 34° S). The Andes at these latitudes are composed of the Neogene Aconcagua fold and thrust belt and the basement-block uplift of the Cordillera Frontal. Detailed mapping has reveled that the structure within the inner part of the fold and thrust belt resulted from both thin and thick-skinned tectonic interactions. In the outer part, displacement is transfered to Mesozoic decollement levels, accounting for a thin-skinned architecture. The border between Argentina and Chile is a region where deformation switches from thin to thick -skinned tectonics. The transition between the two styles coincides with Mesozoic margin-boundary normal faults, suggesting that pre-existing structures and stratigraphy partially controlled the development of the belt. The regional tectonic setting, together with pre-existing extensional structures, constitute the first-order controls in the Neogene deformation history of the area. The geometry of the subducted plate may have influenced the timing and style of deformation in the foreland, but it does not adequately explain the style of deformation within the fold and thrust belt. The presence of an inner thick-skinned part of the belt is correlated with the pre-existing Mesozoic structures.