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_Journal of Structural Geology 32 (2010) 554-565_ _Contents lists available at ScienceDirect_ _Journal of Structural Geology_ _journal homepage: www.elsevier.com/locate/jsg_ _Role of sedimentation during basin inversion in analogue modelling_ _Luisa Pinto a,*, Carolina Muñoz a, Thierry Nalpas b, Reynaldo Charrier a Departamento de Geología, FCFM, Universidad de Chile, Plaza Ercilla 803, Casilla 13518, Correo 21, Santiago, Chile b Géosciences Rennes, UMR CNRS 6118-Université de Rennes 1, Campus Beaulieu, 263 Avenue du General Leclerc, 35042 Rennes Cedex, France_ _article info_ _Article history: Received 8 April 2009 Received in revised form 2 March 2010 Accepted 9 March 2010 Available online 16 March 2010_ _Keywords: Basin inversion Fault reactivation Syntectonic sedimentation Shortcuts Analogue modelling_ _abstract_ _Sand-box experiments were designed to reproduce the effect of sedimentation during extensional basin development and tectonic inversion. These experiments were motivated by growing evidence for tectonic inversion in early Miocene times of an extensional basin (Abanico Basin) in the central Chilean Andes with contemporaneous intense volcanic activity. The experiments perform an extension followed by compression. The first series of experiments were performed without sedimentation in the developing basin; the second series were performed with partial filling of the basin, and the third series with total filling of the extensional basin. The effect of sedimentation on the sides of the basin was also controlled. Compression experiments reproducing tectonic inversion of the previously developed extensional basin were also performed with and without coeval sedimentation (series with null, partial or total fill, and also external sedimentation). The analogue experiments show that high amounts of sediments accumulated during the evolution of an extensional basin enhance subsidence and lead to the development of shortcuts in the footwall of the basin bounding faults during tectonic inversion. During extension the earliest appearance of normal faults occurs in the compartment with the greater sedimentary fill, and this causes asymmetric basin development. The post-extension compressional models show that the greater burden caused by a thicker accumulation of sediments within the basin inhibits tectonic inversion, causing the development of thrust structures rooted in the basin bounding faults. The accumulated sedimentary load affects both the extension and compression phases of the experiments, but has greater influence in the case of sedimentation during extension. A higher burden on the outer edges of the basin compared to the interior enhances the reactivation of normal faults and hampers the development of new thrust structures. The thrust fault(s) originating from the most loaded basin compartment develops as a footwall shortcut from the reactivated fault. With increasing sedimentation the shortcut is developed more superficially. The shortcut absorbs less deformation than the associated main fault._ _© 2010 Elsevier Ltd. All rights reserved._ _1. Introduction_ _The concept of tectonic or structural inversion was generated from the study of petroleum basins (Lamplugh, 1920; Stille, 1924; Pruvost, 1930; Voigt, 1963). Positive tectonic inversion describes those basins that have been initially controlled by extensional faults and later reactivated with a reverse movement during a tectonic compression. Conversely, negative inversion occurs when inverse faults are reactivated with normal movement; however this case is rare (Cooper and Williams, 1989). In this paper, we will refer to positive inversion._ _Analogue modelling has been frequently used to understand the mechanisms involved in the tectonic inversion of basins and the origin of associated structures (e.g. Del Ventisette et al., 2005, 2006). This experimental method is a representation of the natural system with materials similar to those existing on Earth but with a simplified scale. There are several studies that have used analogue modelling to study tectonic inversion. Bally (1984) modeled the inversion process using a hemigraben on a listric fault. He differentiated between partial and total inversion depending on whether there is partial or complete recovery of the pre-graben situation. In the case of total inversion, the reactivation of movement along normal fault(s) results in the recovery of the stratigraphic situation as it was before extension and the extrusion of the basin-fill deposited during extension. The first studies of tectonic inversion used models where a rigid and a mobile block induced the initial geometry of the normal faults (e.g. Bally, 1984; Koopman et al., 1987; McClay, 1989; Buchanan and McClay, 1991, 1992; Mitra, 1993; McClay and White, 1995; Yamada and McClay, 2003a, b). In later models, the experiments were made with free blocks in order to study the geometry and kinematic evolution during extension and compression. Several authors have also analyzed the experimental behavior of several analogue materials including sand, clay and silicone (Richard and Cobbold, 1990; Nalpas and Brun, 1993; Nalpas et al., 1995; Brun and Nalpas, 1996; Keep and McClay, 1997; Dubois et al., 2002; Panien et al., 2005). Furthermore, it has been also shown that to produce inversion along high-angle normal structures in a brittle system modeled by analogue experiments, a non-coaxial angle between the compressive and extensive stresses is required (Brun and Nalpas, 1996; Gartrell et al., 2005), with an optimum angle for inversion close to 15°-14° (Brun and Nalpas, 1996). Other studies have shown that inversion can be generated with higher angles even with orthogonal compression (Del Ventisette et al., 2006). However, these systems have been modeled generally with large ductile silicone basal layers, which creates an experimental device more easily deformable that even produces rotation of blocks on the dip direction of the faults (Brun et al., 1994; Corti et al., 2003; Del Ventisette et al., 2006). An interesting geometry generated in inverted systems results from the development of new thrust faults in the footwall block, named “footwall shortcuts”, that absorb further deformation in the inverted systems (Buchanan and McClay, 1991, 1992); but there is little analysis of their evolution and the specific factors that influence it._ _There are abundant worldwide examples of regions where extension has been followed by tectonic inversion. There are classic cases of inversion in marine environments in North America, and other mountain chains (e.g. Hansen, 1986; Stone, 1989; Walker and Cooper, 1986; Buchanan and Buchanan, 1995; Knott et al., 1995; Lowell, 1995). In the Andean subduction margin, there are good examples of extensional basins, i.e., the Jurassic and Early Cretaceous back arc basins, and the Late Cretaceous and Paleogene intraarc basins, which underwent tectonic inversion (e.g. Jordan et al., 2001; Charrier et al., 2002, 2007). Inversion, in these cases, occurred during major changes of plate dynamics that resulted in modification of the stress regime affecting the continental margin (e.g. Pardo-Casas and Molnar, 1987). A well studied case is the Abanico Basin (e.g. Vergara and Drake, 1979; Nyström et al., 1993, 2003; Kay and Kurtz, 1995; Charrier et al., 2002; Muñoz et al., 2006), developed between Middle Eocene and Late Oligocene times in the Principal Cordillera of central Chile (e.g. Charrier et al., 1994, 2002, 2005; Godoy and Lara, 1994; Burns and Jordan, 1999; Godoy et al., 1999; Jordan et al., 2001; Fock 2005; Fock et al., 2006a, b). In this basin, thick deposits of lava, volcaniclastics and minor sediments were accumulated during extension. Deposition was uninterrupted by the start of the inversion, and continued to form a new and thick volcanic succession (e.g. Charrier et al., 2002, 2005, 2007; Fock 2005; Fock et al., 2006a, b). Therefore, it is particularly interesting to understand how a partial inversion of the basin was possible along with the coeval accumulation of thick volcanic successions. Moreover, the volcanic rocks accumulated during tectonic inversion host giant Late Miocene porphyry CuMo deposits such as Los Pelambres, Río Blanco-Los Bronces and El Teniente, which were emplaced along fault systems associated with the extension and tectonic inversion of the Abanico Basin (Garrido et al., 1994, 2002; Rivera and Cembrano, 2000; Rivera and Falcón, 2000; Charrier et al., 2002, 2005; Godoy, 2005). Deposition coeval to tectonic inversion (i.e. volcanic activity during compression) has not yet been considered by analogue models. In terms of mass transfer, this situation does not correspond to the classic definition of inversion (Voigt, 1963). Some analogue modelling experiments have attempted to assess the influence of sedimentation on basin development, depositing material in the basin at later stages in the extension and pre-compression phases (Nalpas and Brun, 1993; Nalpas et al., 1995; Brun and Nalpas, 1996; Dubois et al., 2002; Panien et al., 2005). These studies show that if there is no sedimentation all normal faults are reactivated to some extent, whereas with sedimentation the reactivation of the structures is limited, generating thrusts and backthrusts that cut and accommodate shortening (Dubois et al., 2002; Panien et al., 2005). However, so far no systematic attempt has been made to evaluate the influence of sedimentation on extensional basin development or the evolution of basin inversion considering all possible cases of syntectonic sedimentation. The inversion associated with deposition of volcanic deposits, and the fact that there are no detailed studies on the subject, has motivated the_ Ключевые слова: partial sedimentation, occurrence, complete, nalpas dubois, correspondent experiment, subsides faster, inverted fault, extensional series, doe, extensional experiment, shortening orthogonal, pinto, schematic illustration, sediment load, fock fock, struct, internal, normal structure, occurrence qext, special, jordan, mm, brun nalpas, grabens order, buchanan buchanan, eds, sandbox experiment, tectonophysics, higher burden, increase, buchanan, partial, panien, movement, society, application, brun, case, compressive experiment, fault, fock, total, mountain, central, orthogonal, compression, internaleexternal sedimentation, normal fault, shortening, los andes, footwall shortcut, extensional basin, doi, wall, graben, vd, view, paper, ext, xed wall, table, pinto journal, geology, internal sedimentation, sediment accumulated, thrust, increased sedimentation, model, grabens, inverted, mobile wall, analogue model, basin inversion, shortening min, la, letouzey, order, ha, geological society, extension compression, mcclay, geol, del ventisette, inverse relationship, sedim itaces, central chile, silicone, deformation, nalpas, journal structural, boundary condition, layer, volcanic succession, result, sedimentation, bull, evolution, higher, structure, dip direction, basin, shortcut, bally, depth, rennes, inversion process, reactivation, produce inversion, inversion, reverse fault, extensional, fault bounding, wa, vertical stress, cm, load, external sedimentation, burden, analogue modelling, sedim, abanico basin, graben inversion, thrust fault, sci, reactivated, time, reactivated fault, london, der, jsg, compressive phase, inversion tectonics, tectonics, voigt, syntectonic sedimentation, experimental device, itaces, direction, vergara, mar, kinematic evolution, gure legend, increased, sand, phase, higher angle, outer edge, geological, generated, structural, developed, analogue, tectonic inversion, experimental, concepci?n, godoy, analogue modeling, angle, rift, absorbed, g?ol, sedimentary load, gradual increase, charrier, analogue experiment, sedimentary, sediment, min, development, experiment someted, dip, journal, internal fault, mobile, external, reverse, increasing sedimentation, elsevier, geometric model, experiment, chile, rev, extension, greater, tectonic, complete sedimentation, series, normal, modelling, displacement, publication, long, partial internal, soc, study, total time, higher load, maximum depth, extensional phase, time difference, dubois, extension absorbed, compressive, thesis universit, kay, structural geology, special publication, petrol