Cenozoic subsidence‐driving mechanisms in the southernmost Patagonian basins of Tierra del Fuego and SW Atlantic

Abstract

Foreland basins are ideal laboratories to examine and quantify forces that contribute to Earth's topography. The interaction of these driving mechanisms (atmospheric, lithospheric and asthenospheric) affects the accumulation and preservation of strata in marine or terrestrial depocentres. For foreland basins that cover thousands of kilometres along orogens, geodynamic processes or lithospheric structure might differ and/or overlap differently along or across strike. The Magallanes-Austral basin in the southernmost Patagonia serves as a good analogue to analyse the interactions between subcrustal forces and foreland sedimentation. While to the northern part of southern Patagonia, Cenozoic basins were predominantly terrigenous and above sea level; at the southernmost end of Patagonia, sedimentation in the island of Tierra del Fuego was mostly submarine. We analysed in this contribution the southernmost foreland of Patagonia by combining backstripping with reconstruction of flexural and dynamic subsidence. These results were compared with terrestrial records exposed further north of southern Patagonia. We found that, in addition to crustal contributions (as deformation and sedimentation), subcrustal forces are required to accommodate the proximal and distal foreland strata and explain the palaeoenvironmental and subsidence discrepancies that resulted after our analysis. When our models are compared with dynamic topographic curves, strong correlations are observed during the Palaeogene, whereas strong topographic differences occurred in the Neogene. Dynamic topography models in the Neogene have reproduced clear uplift, whereas our residual topography results show equilibrium (close to the orogen) to subsidence values (to the distal foreland). We propose that changes in the lithospheric mantle had to work together with the rest of the tectonics and dynamic forces to match 1-D backstripping and flexural curves. This suggests that foreland basins in southern Patagonia were controlled differently along strike the southern Andes and that crustal deformation, asthenospheric flows and a heterogeneous lithospheric mantle structure affected the Cenozoic basin evolution.