SYNOROGENIC FORELAND RIFTING: A REVIEW OF ANDEAN IMPRINTS ON THE EVOLUTION OF TRANSVERSAL BASINS IN SOUTHERN SOUTH AMERICA

GUIDO GIANNI; CESAR NAVARRETE; ANDRÉS FOLGUERA

General Roca

Congreso; XVI Reunión de Tectónica Andina; 2015

AGA

Orogenic-triggered foreland rifting known as impactogene has been documented in current and ancient collisional settings around the world. Sengör, (1976) proposed that indentation of a continental promontory could directly induce foreland extension and/or transtension at a high angle to the orogenic front that usually nucleate in lithospheric anisotropies. Furthermore, far field-stresses associated with collisional events are capable of reactivating pre-existing rift basins in the foreland when properly oriented respect to the imposed contractional stress field (Mats and Perelepova 2011). This peculiar rifting mechanism has been identified in active systems such as the Rhine and Baikal Rifts, related to the Alpine and the Himalayan collision zones respectively. However, the possibility of Andean-type margins to induce this mechanism has not been properly assessed yet. To evaluate the potential of subduction orogenesis to nucleate and/or reactivate extensional basins, we review the most recent advances on the evolution of the Cretaceous to Cenozoic Golfo de San Jorge, Lomas de Olmedo and Taubaté rifts in southern South America and compare them with the uplift history of the Andes (Figure 1).An extensive review of main Andean orogenic stages shows a paradoxical correlation with extensional stages in these transversally disposed rift basins. We interpret these events in terms of a causative relation where rift basins have been influenced at specific times during its evolution by Andean far-field stresses that propagated throughout the foreland area. In the case of the Golfo de San Jorge Basin and Lomas de Olmedo Sub-Basin (Grupo Salta Basin), ENE- and NE-directed Andean contraction would have reactivated normal faults developed in a previous rifting event localized in ancient lithospheric weaknesses (Cominguez and Ramos 1995, Gianni et al.,2014, 2015). At this time, for the particular case of the Grupo Salta Basin the unfavorably oriented Tres Cruces (N-S-trending) and Alemanía (NNE-trending) depocenters experienced thermal subsidence or tectonic inversion (Starck 2011, Steinmtez and Galli 2015). On the other hand, the Taubaté Basin located in the south east margin of Brazil directly opened as a result of the transtensional reactivation of a NE-trending basement fabric under a NE-directed compression related to the Andean Incaic event (Cogné et al., 2013).Obvious differences in the causes driving to impactogenesis (continental collision) as well as particular tectonic and magmatic characteristics respect to the south American cases here described, lead us to differentiate cases of syn-contractional rifting related to continent ?continent collision from those related to ocean-continent collision (Andean-type margins). Hence, in an attempt to develop a broader concept, we propose the use of the term synorogenic foreland rifting for newly developed intraplate rifts that form at a high angle to the orogenic front or reactivations of preexisting rift basins favorably oriented. Under this definition the term impactogene would constitute a specific case of synorogenic foreland rifting. These are characterized by a variable transtensional component depending on their orientation and are directly related to orogenic contractional stress-field involved in continent-continent or ocean-continent collisional settings.