RELATION BETWEEN JURASSIC RIFTING AND ACTIVE WRENCH TECTONICS IN THE SOUTHERNMOST ANDES OF TIERRA DEL FUEGO

GHIGLIONE, M.C.; SUE, C.; BUJALESKY, G.

Universidad de Heidelberg

Simposio; 22nd LAK 2011, Heidelberg; 2011

There is a current general agreement that deformation history of the Fuegian Andes involved late Paleozoic to early Mesozoic compression, Jurassic extension, and a Cretaceous – Paleogene overall compressive regime followed by a Neogene to Recent phase of strike-slip deformation (i.e. Diraison et al. 2000; Menichetti et al. 2008). However, there are several intriguing events such as a late Paleocene-early Eocene phase of extensional deformation related to the opening of Drake Passage (Ghiglione et al. 2008) as well as a Neogene rifting system showing extension parallel to the orogen (see Diraison et al. 2000 and  references therein).  Using seismic lines and field data from the Fuegian fold-thrust belt we reconstruct the interaction between mid-late Jurassic faulting, Andean compression and Neogene strike-slip deformation. The presented structural mapping and serial cross-sections define lateral variations in the structural style and a transversal segmentation of the fold-thrust felt. There is a passage from detachment folds in some segments to fault-propagation folds in others, with similar shortening rates, that may be denoting lateral changes in the rheological properties of the detachment level, as well as changes in depth to basement of each segment, reflecting differential extensional faulting during the mesozoic rifting.  The structural mapping allows to separate the fold-thrust belt north of the Magallano-Fagnano fault system in discrete fault-bounded blocks that were reactivated by strike-slip tectonics. Regarding the presence of widespread quaternary scarps that may be reflecting the presence of active faulting, our mapping allows to distinguish which lineaments are truly the expression of active strike-slip deformation. This  differentiation is partly confirmed by previous paleomagnetic studies (Maffione et al. 2009) and by the distribution of low magnitude (between 2-4 Mb) and mainly superficial (<10 km) earthquakes (Buffoni et al., 2009) that are clustered in close proximity to this lineaments. We propose that due to an orientation match between compressional faults arrays an riedel shears a continuum synergetic transition took place from Middle-Late Eocene compression to Oligocene-Neogene transcurrence.