Deformation bands, early markers of tectonic activity in front of a fold-and-thrust belt: Example from the Tremp-Graus basin, southern Pyrenees, Spain. (May 2018)

• Record Type: Journal Article
• Authors: Robert, Romain; Robion, Philippe; Souloumiac, Pauline; David, Christian; Saillet, Elodie
• Is Part Of: Journal of structural geology. Volume 110(2018)
• Page Start: 65
• Page End: 85
• Publication Date: 2018-05
• Subjects: Deformation bands -- Compaction bands -- Tremp basin -- Anisotropy of magnetic susceptibility -- Layer parallel shortening -- Stress path; Geology, Structural -- Periodicals; Géomorphologie structurale -- Périodiques; Geology, Structural; Periodicals; 551.805
• DOI: 10.1016/j.jsg.2018.02.012
• Languages: English
• ISSNs: 0191-8141

Abstract

Abstract: Strain localization in a porous calcarenite facies of the Aren formation in the Tremp basin was studied. This Maastrichtian syn-tectonic formation exposed in front of the Boixols thrust, in the Central South Pyrenean Zone, hosts bedding perpendicular deformation bands. These bands are organized in two major band sets, striking East-West and N-020 respectively. Both populations formed during early deformation stages linked to the growth of the fold and thrust. A magnetic fabric study (Anisotropy of Magnetic Susceptibility, AMS) was carried out to constrain the shortening direction responsible for the deformation bands development during the upper Cretaceous-Paleocene N-S contraction in the region, which allowed us to define populations of Pure Compaction Bands (PCB) and Shear Enhanced Compaction Bands (SECB) regarding their orientations compared to the shortening direction. Both sets are formed by cataclastic deformation, but more intense in the case of SECBs, which are also thinner than PCBs. The initial pore space is both mechanically reduced and chemically filled by several cementation phases. We propose a geomechanical model based on the regional context of layer parallel shortening, thrusting and strike-slip tectonics considering the burial history of the formation, in order to explain the development of both types of bands at remarkably shallow depths. Highlights: We studied deformation bands in front of the Boixols fold-and-thrust in the Tremp basin. Pure Compaction and Shear Enhanced Compaction bands are defined in the Aren formation. Deformation Bands occurred in a layer-parallel shortening and strike-slip regime. Deformation bands were formed under shallow burial (<1 km) in a calcarenite facies. Possible stress paths were inferred to decipher stress state during syn-tectonic burial.