Influence of attenuated lithosphere and sediment loading on flexure of the deep-water Magallanes retroarc foreland basin, Southern Andes

Abstract

Flexural subsidence in foreland basins is controlled by applied loads-such as topography, water/sediment, and subcrustal forces-and the mechanical properties of the lithosphere. We investigate the controls on subsidence observed within the Upper Cretaceous Magallanes retroarc foreland basin of southern South America to evaluate the impact of lateral variations in flexural rigidity due to Late Jurassic extension. Conventional elastic models cannot explain the observed basin deflection and thick accumulation of deep-water Cenomanian-Turonian basin strata. However, models in which the lithosphere has been previously thinned and deflects under topographic and sedimentary loads successfully reproduce regional subsidence patterns. Results satisfy paleobathymetric observations in the Magallanes Basin and suggest that lithospheric thinning is necessary to produce both long-wavelength and deep subsidence during Late Cretaceous basin evolution. Results indicate that elastic thickness decreases westward from~45-25 km in the distal foreland to~37-15 km beneath the foredeep. These findings are consistent with a westward reduction in crustal thickness associated with the Jurassic extensional history of the Patagonian lithosphere. Our results also show that sediment loading exerts an important control on regional deflection patterns and promotes a wider region of subsidence and reduced forebulge uplift. We propose that lateral variations in mechanical properties and large sediment loads restrict depocenter migration and may cause the foredeep to remain fixed for prolonged periods of time. These findings confirm that loading of thinned lithosphere imposes different mechanical controls on the flexural profile and have potential implications for other retroarc foreland basins characterized by earlier extensional histories.

Lateral Variations in Foreland Flexure of a Rifted Continental Margin: The Aquitaine Basin (SW France)

“…Fosdick et al () propose that an inherited passive margin geometry may localize or “trap” the main depocenter of a foreland basin at its initiation, using the Magallanes retro‐arc foreland basin as a case study. The position of the central Aquitaine Basin above the AAC rift basin may suggest a similar localization role for the inherited rift.…”

“…Many foreland basins are superimposed on ancient rift systems, which may also have a fundamental influence on their evolution (e.g., DeCelles et al, ; Desegaulx et al, ; Horton et al, ; Watts, ; Willett et al, ). While several studies suggest that inherited rift structures may weaken the lithosphere and thus reduce Te (e.g., Papua New‐Guinea, Haddad & Watts, ; Taiwan, Lin & Watts, ; Southern Andes, Fosdick et al, ), a detailed study of this topic is lacking. In addition, depending on the thermal age of the rifted lithosphere at the onset of convergence, a component of postrift thermal subsidence may actively contribute to foreland subsidence (e.g., Desegaulx et al, ).…”

Along-strike variation in crustal shortening and kinematic evolution of the base of a retroarc fold-and-thrust belt: Magallanes, Chile 53°S-54°S

“…Cretaceous-Neogene crustal shortening and thickening were accompanied by the formation of the flexural Magallanes foreland basin (Fosdick et al, 2014;Figs. 1 and 2).…”

Constraints on deformation of the Southern Andes since the Cretaceous from anisotropy of magnetic susceptibility

“…8 faults and crustal attenuation that are thought to have played a key role during later foreland propagation of the deformation (Winslow, 1982;Fosdick et al, 2011Fosdick et al, , 2014Likerman et al, 2013). The first sedimentary infill of the marginal basin is represented by the Upper Jurassic to Lower Cretaceous submarine silicic volcanics and volcaniclastic levels of the Tobifera (or Lemaire) formation, and dark mudstones of the Yahgan (or Zapata) formation, followed by slope mudstones of the Beauvoir Formation (Wilson, 1991;Fildani and Hessler, 2005;Olivero and Malumián, 2008;Menichetti et al, 2008;Klepeis et al, 2010).…”

“…It has been already pointed out the key role of pre-existing Jurassic normal faults rooted in the basement of the South American continental margin in the evolution of the Magallanes foreland basin sedimentation and subsequent deformation (Menichetti et al, 2008;Likerman et al, 2013;Fosdick et al, 2011Fosdick et al, , 2014Ghiglione et al, 2013).…”