A flexural isostatic model of lithosphere shortening and foreland basin formation: Application to the Eastern Cordillera and Subandean belt of NW Argentina

Abstract

A numerical model of lithosphere shortening has been developed to combine flexural isostatic and structural balancing. This allows us to quantitatively reconcile lithosphere shortening, thrust sheet emplacement, and foreland basin formation. Lithosphere shortening is accommodated by thrusting in the upper crust and by distributed deformation in the lower crust and the lithospheric mantle. This leads to loading by thrust sheet emplacement, crustal thickening, and thermal perturbation. Additional loading and unloading are generated by sedimentation and erosion, respectively. The model is kinematically controlled, each fault having its position, geometry, and movement prescribed. The model is applied to the Subandean late Oligocene to Recent foreland fold and thrust belt of NW Argentina at 22°15′S. The Subandean belt of NW Argentina contains three major stratigraphic units, the Lower, Middle, and Upper Terciario Subandino Formations. By modelling these formations we attempt to determine whether the Terciario Subandino Group can be explained as a foredeep fill in response to thrust sheet loading, and, if so, what is the required effective elastic thickness. A successful model must predict not only foreland stratigraphy but also exhumation, topography, and crustal thickness. We see a change in the wavelength of sedimentary deposition in the Subandean basin through time that can be accounted for by a change in flexural rigidity. Accommodation space for the Lower Terciario Subandino Formation can be generated using an elastic thickness of 70 km. For the Middle/Upper Terciario an elastic thickness of 15 km produces the correct basin geometries. Shortening estimates of 110 km have proved sufficient to generate the observed foreland stratigraphy, Bouguer anomaly, and topography across the Subandean belt and Eastern Cordillera. However, an additional 140 km of shortening is required to generate the observed Bouguer anomaly and topography across the western Andes. This discrepancy could be due to earlier shortening in the western Andes or to crustal thickening by magma addition.

Mechanical aspects of sedimentary basin formation: development of integrated models for lithospheric and surface processes

“…This approach has the capability to integrate in an adequate way constraints provided by structural geology with basin modeling in compressional settings. Such constraints can result from analog modeling (see Brun and Nalpas 1996), computer modeling (see Sassi et al 1993;Zoetemeijer et al 1993;Roure and Sassi 1995;Toth et al 1996), seismic reflection data, and field studies in onshore and offshore basins (see Roure et al 1996b). These models can also be linked with the large-scale flexural models discussed above.…”

Modeling the evolution of the Guadalquivir foreland basin (southern Spain)

“… Flemings and Jordan [1989] incorporated wedge‐progradation gradual loading and sedimentation. Later, Toth et al [1996] and Ford et al [1999] explicitly related loading with thrusting in the active margin of the sub‐Andean foreland and the western Alps, respectively. Many among these and other works found that the load derived from the present topography or the thrust kinematics cannot satisfactorily explain the basement deflection.…”

“…In particular, we propose a self‐consistent quantitative model for the evolution of the Guadalquivir Basin (southern Spain) linking the emplacement of the Betic Range, the subcrustal mass redistribution, and the rheology of the flexed lithosphere. For this purpose, we apply a numerical code based on Garcia‐Castellanos et al [1997] that allows the calculation of the flexural subsidence of a multilayered lithosphere (in a similar way to Waschbusch and Royden [1992] and Burov and Diament [1992, 1995]) when loaded by noninstantaneous thrusting and erosion/sedimentation processes (similar to Toth et al [1996]).…”

Interplay between lithospheric flexure and river transport in foreland basins

“…Since the early quantitative studies of foreland basin formation (Beaumont, 1981; Jordan, 1981), it is generally accepted that the sedimentary record of these basins is related to the flexural response of the continental lithosphere to orogen loading. Later numerical models incorporated non‐instantaneous wedge loading and sedimentation processes (Flemings & Jordan, 1989; Toth et al ., 1996; Ford et al ., 1999) finding that larger sedimentary basins are expected at higher transport rates and higher lithospheric rigidity (Flemings & Jordan, 1989). Other authors investigated the role of the lithospheric rheological stratification on the geometry of the sedimentary infill (Waschbusch & Royden, 1992; Garcia‐Castellanos et al ., 1997, 2002).…”