The role of pre-existing faults in basin evolution: constraints from 2D finite element and 3D flexure models

Abstract

Abstract:The lithospheric driving forces which cause intraplate basin deformation are relatively constant over large areas. Consequently, lateral variations in deformation and stress and strain concentrations seem to be primarily caused by (pre-existing) heterogenities in the rheological signature of the continental lithosphere underlying the sedimentary basins. In this paper, we explore the weak character of upper crustal faults and their control on basin shape for a number of case studies on intraplate Phanerozoic basin settings, using a 2D finite element and a 3D flexure model. Of key importance is the integration of seismic data and field observations with the tectonic modelling, allowing the investigation of deformation processes and their expressions on different scales, operating on different levels of the lithosphere. Finite element models for sub-basin scales, incorporating weak upper crustal faults, predict strong control of these weak zones on local stress distributions and subsequent deformation, in agreement with observed deformation patterns. Slip along upper crustal faults control stress distribution and subsequent faulting in overlying sedimentary rocks. The effect of weak upper crustal fault movements on basin-wide (regional) upper crustal flexure is looked at in two case studies on: (1) extensional tectonics in the Lake Tanganyika Rift Zone (East Africa); and (2) compressional tectonics in the Central System and Tajo Basin (Central Spain). Both settings indicate that basement warpings are controlled by large amounts of slip along so-called weak crustal-scale border faults, which are mostly planar. Adopting border fault displacements in the 3D flexure model, the results indicate low effective elastic thickness (EET) values in a range of 3-7 km for induced basement deflection patterns in accordance with observations. The low EET values most likely reflect a (partly) decoupling of upper crustal and subcrustal deformation, facilitated by the weak lower crust, and in agreement with standard rheological assumptions for Phanerozoic lithosphere. In contrast, the inferred weakness of upper crustal faults relative to surrounding rock is not evident from uniform rheological assumptions. However, observations of reactivations of faults which are not preferably aligned with the stress field, and reactivations of basin deformation on long time-scales are in support of this feature.

Determination of present-day stress tensor and neotectonic interval in the Spanish Central System and Madrid Basin, central Spain

“…The western limit of these facies seems to control the formation of these detachments (Van Wees et al, 1995). However, the presence of important basement faults also influences the localization of the thrust and fault propagation folds (Perucha et al, 1995).…”

“…It could suggest a flexural response to the main tectonic event having occurred before in the Middle Miocene, as can be deduced from flexural analysis to determine the effective elastic thickness (EET) of the area (Van Wees et al, 1995).…”

Strength of the Iberian intraplate lithosphere: Cenozoic deformations and seismicity

“…From the above discussion, the integrated strength of the Iberian intraplate ranges from 9.5 x 10 12 to 1.4 x 10 13 N m Wees et al 1996;Tejero and Ruiz, 2002;Pérez-Gussinyé and Watts, 2005;Gómez-Ortiz et al, 2005b;Tesauro et al, 2007;Martín-Velázquez et al, 2008;Jiménez-Díaz et al, 2012) and they decrease from the sedimentary basins toward the mountain range (Figs. 4b,c and 5b,c).…”

“…e T have been limited by flexure modelling to 7 km in the Madrid Basin (Van Wees et al, 1996), and by Bouguer coherence and free-air admittance methods to 15-30 km and 30-40 km, respectively, for the entire centre of Iberia (Gómez- Ortiz et al, 2005b;Pérez-Gussinyé and Watts, 2005). The strength envelopes provide different estimates for the basins and the Central System (Gómez- Ortiz et al, 2005b): ~17 km/~26.5 km (wet/dry rheologies) and 13 km/22 km (wet/dry rheologies) respectively.…”

“…The stress regime is complex and seismicity is low to moderate Herraiz et al 2000;De Vicente et al 2007;Giner-Robles et al 2012). Several studies have addressed the estimate of lithospheric strength to explain these characteristics (Van Wees et al, 1996;Gómez-Ortiz 2001;Tejero and Ruiz 2002;Gómez-Ortiz et al, 2005b;Pérez-Gussinyé and Watts 2005;Jiménez-Díaz et al, 2012). Although strength strongly depends on the structure, temperature, composition, strain rate and stress regime of the lithosphere (Fernàndez and Ranalli 1997;Afonso and Ranalli 2004;Ruiz et al, 2006;Fernández-Ibáñez and Soto 2008;Burov 2011;Jiménez-Díaz et al, 2012), average crustal and mantle structures over large areas, diverse lithologies (hard/ soft) and stress regimes (compression/tension) were assumed in those previous studies.…”