Patagonian broken foreland and related impactogene: The origin of the Chubut Basin.

GIANNI, G; NAVARRETE, C; ORTS, D; TOBAL, J., FOLGUERA, A

TECTONOPHYSICS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2015 vol. 1 p. 1 - 1

0040-1951

The Central Patagonia is characterized by prominent continental deposits that belong to theCretaceous Chubut Group Basin, whose tectonic setting remains controversial. It has been interpretedas a foreland basin, an extensional basin and even as a sag stage of a rift event. Related depositsoutcrop as part of the Patagonian broken foreland, east of the Patagonian Andes. Particulary, the SanBernardo fold and thrust belt, between 42°-48ºS, as the main sector of the broken foreland, constitutesa NNW-trending intraplate belt located 450 km away from the trench. Coincidentally, at these latitudes,1,200 km east of the trench, intraplate deformation has caused tectonic inversion of Mesozoic basinspresently located at the Atlantic offshore area. Additionally, at the San Jorge Gulf area this orogenicsystem interferes with a conspicuous E-W extensional system, transversaly disposed to the Andeanstrike, mainly active between the late Early Cretaceous and late Paleocene. We carried out anintegrated analysis from structural, 2-D and 3-D seismic data at the San Bernardo FTB and the adjacentRío Mayo Basin, studying sections of the Chubut Group Basin to unravel the different evolutionarystages. Thus, surface and subsurface evidence of syn-compressional deposition indicate thedevelopment of a broken foreland basin related to the formation of the San Bernardo FTB, suggestingan initial growth during the late Early Cretaceous and probably up to the late Paleocene. Our resultsimply that the Cretaceous compression acted in concert with transversal foreland extension. Hence, wepropose a syncontractional rift reactivation of a potential lithospheric anisotropy, triggered by regionalcontraction. Finally, the origin of compression during this time is discussed in relation to multipleprocesses that go from high convergence between plates and trenchward motion of South America,collision of mid-ocean rigdes, to potential dip changes in the subducted slab, as suggested by arcexpansion.