Patagonian broken foreland and related synorogenic rifting: The origin of the Chubut Group Basin

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

TECTONOPHYSICS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2015 vol. 649 p. 81 - 99

0040-1951

The Central Patagonia is characterized by prominent continental deposits that belong to the Cretaceous Chubut Group Basin,whose tectonic setting remains controversial. It has been interpreted as a foreland basin, an exten- sional basinand even as a sag stage of a rift event. Related deposits outcrop as part of the Patagonian brokenfore- land, east of the Patagonian Andes. Particulary, the San Bernardo fold and thrust belt, between 42° and 48°S, as themain sector of the broken foreland, constitutes a NNW-trending intraplate belt located 450 km away from the trench. Coincidentally, at these latitudes, 1200 km east of the trench, intraplate deformation has caused tec- tonic inversion of Mesozoic basins presently located at the Atlantic offshore area. Additionally, at the San Jorge Gulf area this orogenic system interferes with a conspicuous E?Wextensional system, transversally disposed to the Andean strike, mainly active between the late Early Cretaceous and late Paleocene. We carried out an in- tegrated analysis fromstructural, 2-D and 3-D seismic data at the San Bernardo FTB and the adjacent RíoMayo Basin, studying sections of the Chubut Group Basin to unravel the different evolutionary stages. Thus, surface and subsurface evidence of syn-compressional deposition indicate the development of a broken foreland basin related to the formation of the San Bernardo FTB, suggesting an initial growth during the late Early Cretaceous and probably up to the late Paleocene. Our results imply that the Cretaceous compression acted in concert with transversal foreland extension. Hence,we propose a syncontractional rift reactivation of a potential litho- spheric anisotropy, triggered by regional contraction. Finally, the origin of compression during this time is discussed in relation tomultiple processes that go fromhigh convergence between plates and trenchwardmo- tion of South America, collision of mid-ocean ridges, to potential dip changes in the subducted slab, as suggested by arc expansion.