CONCAVE-TO FORELAND INDENTER AND THE FORMATION OF AN ARCUATE THRUST SYSTEM IN SANDBOX EXPERIMENTS: A COMPARISON WITH THE SOUTHERNMOST ANDES

One of the most conspicuous large-scale features of the entire Andean chain is the progressive change in strike from the N-S oriented Patagonian Andes to the E-W trending Fuegian Andes. This bend was originally named the “Patagonian Orocline” assuming complete oroclinal bending. However, the kinematic evolution of the bend is still a matter of discussion, and the possibility to disclose the overall tectonic history of the region hinge in determine whether the southernmost Andes are a truly Orocline, or if they evolved as a primary bend.

Although paleomagnetic studies could be a useful tool to unveil the kinematic evolution of the curve through the analysis of declination anomalies, paleomagnetic data from the region is still very scarce and show an irregular pattern of rotations. However, the region was affected by multiple phases of spatially superimposed deformation since the Paleozoic, including many processes that may have produce vertical-axis rotations.

We use analogue experiments to test whether the map-shape of the southernmost Andes and its structural features can be related to Tertiary oroclinal bending or if to the contrary they are a recess since at list the Late Cretaceous. The focus was made on the interaction between the basement-internal domain and the thin – skinned fold-thrust belt. Since the Cordilleran basement-domain became tectonically consolidated during Late Cretaceous times, we consider that it behaved as a rigid indenter colliding against the soft tertiary sedimentary cover. The experiments described in this work investigate three possible tectonic configurations, including the oroclinal hypothesis with rotational indentation, and the primary bend theory: two-phase indentation and diagonal indentation. A geometry of concave-to-foreland-indenter is in agreement with the structural pattern and the along-strike variations of orogenic shortening. Further work is necessary to test the influence of the Late Cretaceous Rocas Verdes-marginal basin closure in the formation of the promontory.