Counterclockwise rotation during the Cenozoic in the northwestern end of
the Sierras Pampeanas, Argentina
Abstract
Investigations on the Andean orocline revealed that it is characterized
to the north by counterclockwise rotation of about 37° and, to the
south, due to an clockwise rotation of about 29°. This rotation would
have begun in the Upper Eocene as a consequence of the convergence of
the Nazca and South American plates. In the transition zone between the
Puna and the Sierras Pampeanas show a pattern of clockwise rotations.
Our paper shows that the NE convergence of the plates generated the
counterclockwise rotation of the NW end of the Sierras Pampeanas. The
counterclockwise rotation of the mountain blocks of approximately 20°
would have occurred on a horizontal plane within 10 to 15 km of depth
favored by the caloric rise during magmatic activity at 13 Ma. The
rotations of this set of mountain ranges generated local stress tensors
with NE and NW strike that conditioned the development of valleys,
basins, mineralized dikes, mineral deposits and disassociated alluvial
fans from their origins. The Atajo fault had a ductile and brittle
behavior. Its reverse vertical component disposes a mylonitic belt of
the Sierra de Aconquija on the rocks of the Ovejería Block and the
Farallón Negro Volcanic Complex and, its dextral horizontal component,
developed curvatures that gave rise to pull apart basins and positive
zones. It is probable that towards the Lower Miocene the Santa María
valley, the Campo del Arenal, the Hualfín valley and the Pipanaco salt
flat formed a large basin, barely interrupted by hills of very little
relief.