Linkage between Neogene arc expansion and contractional reactivation of a Cretaceous fold-and-thrust belt (southern Central Andes, 36º-37ºS)

SPAGNUOLO, M. G; FOLGUERA A.; RAMOS V. A

Niza, Francia

Simposio; 7th International Symposium on Andean Geodynamics; 2008

The Andean margin between 34º and 37º south latitude is considered a key area in order to constrain plate motion dynamics and especially the geometrical relation between the overriding and the subducting plate through time. Variations in the Wadatti-Benioff zone during the last 20 My strongly affected and controlled foreland deformation and emplacement of anomalously thick accumulations of arc-related rocks far away from the trench. Here, we analyze Miocene arc expansion, which may be related to shallowing of the subduction zone and related to a maximun in uplift and deformation during that time. The region was affected by intense compression since Late Cretaceous times. Magmatic activity is generally explained by a progressively intense subduction coupling at the western plate margin and alternations between normal and flat subduction stages. Variations in the Wadatti-Benioff zone during the last 20 My at these latitudes strongly affected and controlled foreland deformation and emplacement of anomalously thick accumulations of arc-related rocks far away from the trench (Kay  et al., 2006). The Late Miocene orogenic front at 36ºS extended as much as 430 km from the Pacific trench and was associated with arc-related products with mean ages around 11 Ma (Ramos and Folguera, 2005). All this magmatic activity was superimposed to the Cretaceous fault-and-thrust belt that partially controlled the emplacement of the volcanic products during the Miocene contractional phase. Slab flattening have produced migration of volcanic arc and the reactivation of the basement structures that deformed the Miocene deposits.