Structure of the Southern Andes between 36-39ºS

ROJAS VERA, E.; ORTS, D.L.; SPAGNUOLO, M.; SAGRIPANTI, L.; GIMENEZ, M.; RUIZ, F.; MARTINEZ, P.; ZAMORA VALCARCE, G.; BOTTESI, G.

Antofagasta

Congreso; XIII Congreso Geológico de Chile; 2012

Universidad Católica del Norte

One of the main morphological changes along the Southern Central Andes occurs in the segment from 36º-39ºS The northern section is characterized by prominent basement structures, a relatively deep level of exhumation and a thick skinned orogenic front that conforms a topography with important areas over 2,000 m. Contrastingly, the southern part is formed by mildly inverted basement structures mainly restricted to the hinterland zone that determined a much lower topography than to the north, reaching locally 1,500-1,700 m. Through the construction of regional balanced cross sections across the Andes, constrained by field and geophysical data, variable contribution of main contractional stages was quantified. Extensional reactivations described for this segment in Late Oligocene-Early Miocene and Pliocene to Quaternary times, after the two main contractional episodes, seem to have stretched the crust in only less than 3 km respectively. It is therefore determined that those morphological and structural differences were associated with contrasting degrees of Neogene shortening, while Late Cretaceous to Eocene contractions have been nearly constant through latitude. Variable Neogene arc expansion described for this area could be the clue for contrasting achieved contractional deformations. While to the north Late Miocene arc related rocks covered most of the retroarc zone, presumably driven by a shallow subduction episode in the area, to the south they remained restricted to the drainage divide. Other factors, involving architecture of previous rifts in the zone are also proposed as additional mechanisms that accommodated through inversion variable shortening magnitudes.