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Symétrie et asymétrie des rifts et mécanismes d'amincissement de la lithospère
... Where the internal deformation of crustal-scale models can in some cases be partly observed via a glass sidewall (while accounting for boundary friction effects), the internal deformation of lithosphere-scale models remains elusive since the model lithosphere generally contains different (sticky viscous) layers that hamper direct observation of the model interior through glass. These viscous layers also hamper the use of surface structures and topography (including the topography of the base of the lithosphere, e.g., Nestola et al., 2013Nestola et al., , 2015 as reliable indicators for internal deformation since these layers often decouple internal model deformation from the surface structures (e.g., Allemand et al., 1989;Molnar et al., 2017Molnar et al., , 2018Zwaan et al., 2019Zwaan et al., , 2021Zwaan, Chenin, et al., 2022; Figure 1). Sectioning is another Allemand and Brun (1991). ...
... As described in the preceding paragraph, a degree of coupling related to a moderate divergence rate is needed for this deformation transfer, which occurs along two shear zones in the lower crustal layer. The development of such double shear zones and associated double graben structures has been observed in both lithospheric-scale analog models (e.g., Brun & Beslier, 1996;Michon & Merle, 2000Nestola et al., 2015), as well as in crustal-scale brittle-viscous models, where instead of a seed the edge of a base plate (VD) represents a fault in the upper lithospheric mantle (e.g., Allemand et al., 1989;Michon & Merle, 2000Zwaan et al., 2019Zwaan et al., , 2021Zwaan, Chenin, et al., 2022). Moreover, they are also observed in numerical modeling studies (Chenin et al., 2018(Chenin et al., , 2020Dyksterhuis et al., 2007;Oliveira et al., 2022). ...
... In both cases we find a sharp rise of the asthenosphere, isostatically compensating the strong thinning of the lithosphere, which in the center chiefly consists of upper crustal and lower lithospheric mantle material as both the lower crust and upper lithospheric mantle are practically split in two (Figure 6g, 6n, 7, 12c, 12f). This rise of the asthenosphere is a universal observation in other lithospheric-scale analog and numerical models undergoing strongly localized thinning (e.g., Allemand et al., 1989;Brun & Beslier, 1996;Brune et al., 2014;Chenin et al., 2018Chenin et al., , 2020Nestola et al., 2013Nestola et al., , 2015, and prevents the local "collapse" of the modeled lithosphere that may occur in advanced stages of rifting if no such isostatic compensation is included. Furthermore, there is no unrealistic regional subsidence of undeformed parts of the lithosphere due to stretching of the model and viscous thinning of lower crustal layer, previously observed in two-layer brittle-viscous models (e.g., Schmid et al., 2022aSchmid et al., , 2022bZwaan et al., 2020). ...
Rifting and continental break-up are fundamental tectonic processes, the understanding of which is of prime importance. However, the vast temporal and spatial scales involved pose major limitations to researchers. Analog tectonic modeling represents a great means to mitigate these limitations, but studying the complex internal deformation of lithospheric-scale models remains a challenge. We therefore present a novel method for lithospheric-scale rifting models that are uniquely monitored in an X-ray CT scanner, which combined with digital image correlation (DIC) techniques, provides unparalleled insights into model deformation. Our first models illustrate how the degree of coupling between competent lithospheric layers, which are separated by a weak lower crustal layer, strongly impacts rift system development. Low coupling isolates the upper crust from the upper lithospheric mantle layer below, preventing an efficient transfer of deformation between both layers. By contrast, fast rifting increases coupling, so that deformation in the mantle is efficiently transferred to the upper crust, inducing either a symmetric or asymmetric (double) rift system. Furthermore, oblique divergence may lead to en echelon graben arrangements and delayed exhumation of the lower crustal layer. The successful application of our novel modeling approach, yielding these first-order insights, provides a clear incentive to continue running lithospheric-scale rifting models, and to apply advanced monitoring techniques to extract as much information from models as possible. There is indeed a broad range of opportunities for follow-up studies within (and beyond) the field of rift tectonics.
... A standard model setup for brittle-ductile settings involves a base plate system with a viscous layer representing the ductile lower crust and an overlying brittle layer simulating the upper crust ( Figure 6.1c, for example, Allemand et al. 1989;Tron and Brun 1991;Merle 2000, 2003). Note that we could also use such a brittle-viscous layering for simulating a detachment (e.g. ...
... In this case, four-layer models representing the brittle and viscous parts of the lithosphere are mostly used, although modelers have also worked with three-layer systems (e.g. Allemand et al. 1989). A very weak viscous layer such as honey or glucose syrup acts as an analogue for the asthenosphere. ...
... A base plate setup causes localized deformation above the velocity discontinuity (VD), yet depending on strain rate a single or double rift may develop (source: modified after Merle 2000, 2003). Furthermore, asymmetric extension may (in some cases) deflect deformation away from the VD (Allemand et al. 1989); g and h) Effects of sedimentation on rift development. Sedimentary infill causes strengthening of the brittle layer, focusing fault activity along a few faults and suppressing upwelling of viscous material. ...
Rifted margins are major geological objects that mark the transition between continents and oceans, the two first‐order types of land masses present on Earth. Rifted margins and offshore rift basins are of high interest for many various reasons. Rifted margins include several morphologically distinct entities: continental shelf, continental slope, continental rise, and abyssal plain. Rifted margins are extremely diverse, and encompass a variety of geometries, basement compositions and sedimentary architectures that, in turn, indicate differences in temporal and spatial evolution. The chapter reviews the evolution of knowledge on rift and rifted margin evolution and architecture, from the pioneering models that defined the fundamental physical rules governing lithospheric extension to modern conceptual models and today's consensus and debates. Modern concepts now include polyphase, in‐and‐out of sequence fault‐systems, concave‐downward detachments, zones of newly accreted basement with low‐angle top‐basement fault surface, among others.
... A standard model setup for brittle-ductile settings involves a base plate system with a viscous layer representing the ductile lower crust and an overlying brittle layer simulating the upper crust ( Figure 6.1c, for example, Allemand et al. 1989;Tron and Brun 1991;Merle 2000, 2003). Note that we could also use such a brittle-viscous layering for simulating a detachment (e.g. ...
... In this case, four-layer models representing the brittle and viscous parts of the lithosphere are mostly used, although modelers have also worked with three-layer systems (e.g. Allemand et al. 1989). A very weak viscous layer such as honey or glucose syrup acts as an analogue for the asthenosphere. ...
... A base plate setup causes localized deformation above the velocity discontinuity (VD), yet depending on strain rate a single or double rift may develop (source: modified after Merle 2000, 2003). Furthermore, asymmetric extension may (in some cases) deflect deformation away from the VD (Allemand et al. 1989); g and h) Effects of sedimentation on rift development. Sedimentary infill causes strengthening of the brittle layer, focusing fault activity along a few faults and suppressing upwelling of viscous material. ...
Rifts can be summarized as geographical regions consisting of extensional sedimentary basins of various sizes, with various tectonic and sedimentary geometries that are linked in various structural contexts. This chapter provides a list of the main types of rifts and case examples. It provides the definition of the active and passive rifting categories, as these are regularly mentioned in the literature and are the primary designations of extensional rift settings. The chapter lists the major tectonic structures and basin types encountered in rifts and rifted margins. Subsidence is the stage that leads to the progressive deepening of the basin floor and hence allows the accumulation of sediments in rift basins. It is the process by which the lithosphere regains isostatic equilibrium. Sedimentation, although always present in rift basins, is extremely variable from one system to the other. Traditionally, sedimentary sequences of rift basins are subdivided into three categories: pre‐, syn‐ and post‐rifts.
... 204Allemand et al. 1989). A very weak viscous layer such as honey or glucose syrup is used as 205Examples of model set-ups in section view6 an analogue for the asthenosphere. ...
... e.g.Tron & Brun 1991, Allemand et al. 1989Michon & Merle 2000. Note 176 that one could also use such a layering for simulating a detachment (e.g. ...
This chapter describes how analogue modeling techniques have been used to study a wide variety of aspects associated with rifting processes, from normal fault development to lithospheric necking towards continental breakup. When using analogue modeling techniques, proper scaling is necessary to guarantee geometrical, kinematic and dynamic similarity between a model and its natural equivalent. Researchers have been using increasingly sophisticated techniques to monitor deformation in their analogue experiments. The most basic option, used since the early days of modeling, is photography. The chapter provides an overview of various examples, ranging from quasi‐2D models of crustal and lithospheric scale experiments, to models involving 3D rift processes, such as oblique extension, rift segment interaction and rotational rifting. When zooming out and applying brittle‐viscous layers representing the entire brittle‐ductile crust, researchers have found various influences of lithospheric strength as well as model boundary conditions on the mode of rifting.
... Pour la première série d'expériences Bre 1 à Bre 4, le dispositif expérimental consistait en une plaque basale rigide fixe sur laquelle une plaque mobile mince fixée à une paroi latérale mobile induit une discontinuité de vitesse (DV) à la base du modèle (Figure 3.1f), qui localise la déformation (cf. Malavielle, 1984 ;Balé, 1986 ;Allemand et al. 1989 ;Ballard, 1989 ; , préservés le long des reliefs. Le piémont de Sfakion présente une plaine côtière apparente sur environ 20 km de long et de 1,5 à 2,5 km de large, d'est en ouest, limitée au nord par une faille normale majeure orientée E-W ("Faille Sfakia", Carte du système complexes de cônes alluviaux du piémont de Sfakion, montrant les trois principales divisions stratigraphiques (stades de dépôt) et les escarpements topographiques . ...
Les brèches sédimentaires proviennent d’une grande diversité de processus physiques. L’identification de ces processus de formation est cruciale pour les replacer dans un contexte paléoenvironnemental et géodynamique. Dans un premier temps, nous nous sommes intéressés aux processus de formation et de préservation des brèches sédimentaires colluviales dans un contexte extensif, en comparant un système récent crétois et un système ancien pyrénéen. Les résultats de terrain, associés à une approche par modélisation analogique, montrent que lorsque les brèches sédimentaires de cône colluvial sont préservées, elles correspondent à des dépôts syntectoniques de bordure de bassins extensifs et peuvent être ainsi considérées comme un indicateur sédimentaire du stade initial de l'extension continentale. Une nouvelle nomenclature est aussi proposée pour les faciès de brèches sédimentaires de cône colluvial typiques des processus de chute de pierre, d'éboulement et de glissement rocheux. Enfin cette première étude a permis de mettre en évidence l'importance d'une phase tectonique extensive au Jurassique supérieur dans les Pyrénées Orientales. Dans un second temps, nous nous sommes intéressés à l'évolution diagenétique et la datation des brèches du flanc sud du synclinal du Bas Agly au NE des Pyrénées. Ces brèches ont été le sujet de nombreuses controverses quant à leur âge, leur genèse et leur contexte paléoenvironnemental. Cette étude nous a permis d’apporter un éclaircissement sur l’évolution tectonique et paléogéographique du domaine NE pyrénéen. Plus largement nous proposons des pistes méthodologiques d’analyse des brèches sédimentaires dans l’optique d’éclaircir leur signification géodynamique.
... Base plate or conveyer belt set-ups have been commonly used for modelling extensional tectonics (Allemand et al., 1989;Allemand and Brun, 1991;Brun and Tron, 1993;Keep and McClay, 1997;Merle, 2000, 2003;Gabrielsen et al., 2016;Zwaan et al., 2019) (Fig. 5g). The edge of the base plate or conveyor belt creates a velocity discontinuity (VD) representing a fault or shear zone in the basement or upper mantle that localizes deformation in the overlying model materials as the plate is pulled out from under them, resulting in the development of a rift basin (Fig. 5g). ...
Basin inversion involves the reversal of subsidence in a basin due to
compressional tectonic forces, leading to uplift of the basin's sedimentary
infill. Detailed knowledge of basin inversion is of great importance for
scientific, societal, and economic reasons, spurring continued research
efforts to better understand the processes involved. Analogue tectonic
modelling forms a key part of these efforts, and analogue modellers have
conducted numerous studies of basin inversion. In this review paper we recap
the advances in our knowledge of basin inversion processes acquired through
analogue modelling studies, providing an up-to-date summary of the state of
analogue modelling of basin inversion. We describe the different definitions
of basin inversion that are being applied by researchers, why basin
inversion has been historically an important research topic and what the
general mechanics involved in basin inversion are. We subsequently treat the
wide range of different experimental approaches used for basin inversion
modelling, with attention to the various materials, set-ups, and techniques
used for model monitoring and analysing the model results. Our new systematic overviews of generalized model results reveal the diversity of these results, which depend greatly on the chosen set-up, model layering and
(oblique) kinematics of inversion, and 3D along-strike structural and
kinematic variations in the system. We show how analogue modelling results
are in good agreement with numerical models, and how these results help researchers to
better understand natural examples of basin inversion. In addition to
reviewing the past efforts in the field of analogue modelling, we also shed
light on future modelling challenges and identify a number of opportunities
for follow-up research. These include the testing of force boundary
conditions, adding geological processes such as sedimentation, transport, and
erosion; applying state-of-the-art modelling and quantification techniques;
and establishing best modelling practices. We also suggest expanding the
scope of basin inversion modelling beyond the traditional upper crustal
“North Sea style” of inversion, which may contribute to the ongoing search
for clean energy resources. It follows that basin inversion modelling can
bring valuable new insights, providing a great incentive to continue our
efforts in this field. We therefore hope that this review paper will form an
inspiration for future analogue modelling studies of basin inversion.
... In order to place the thinning mode of the NPZ basins into a more theoretical context, it is important to recall that two major exclusive or complementary deformation regimes control the structure of extended domains: simple shear and pure shear. Most of the concepts attached to these contrasted tectonic regimes were shown and discussed by the pioneers McKenzie (1978), Wernicke (1981, Lister and Davis (1989) and Lister et al. (1991), and many debates on the symmetry or lack of symmetry of lithospheric and crustal thinning processes have thus flourished (Buck et al. 1988;Allemand et al. 1989;Buck 1991Buck , 1999) (Questions about the symmetry of hyper-extending systems are also discussed when considering the structure of current passive continental margins; Reston et al. 1995;Michon and Merle 2003;Huismans and Beaumont 2007;Reston and Pérez-Gussinyé 2007;Sutra et al. 2013;Brune et al. 2014.) The fundamental questions regarding the relative importance of ductile versus brittle regimes of deformation during continental extension also apply to the evolution of smooth-slope basins. ...
The margins of the North Atlantic Ocean, including the Newfoundland and Iberian Margins, present two distinct episodes of rifting: at Permian–Trias times and in the middle Cretaceous. In the South Atlantic Ocean, rifting occurred on the location of the Pan‐African suture, more than 450 Ma after its formation, and the two events are clearly dissociated. At first order, the geodynamic segmentation of the South and Equatorial Atlantic Oceans leads to the formation of different types of passive margins, showing a relationship between the regional geodynamic context and the structural architecture of passive margins. The Central Segment of the South Atlantic Ocean is characterized by sedimentary basins with pre‐ and syn‐break‐up magmatism, and the presence of an approximately 1–2 km‐thick salt layer in the so‐called continent‐ocean transition, overlying a mainly non‐marine sequence.
The North Pyrenean Zone (NPZ) belongs to the northern flank of the Pyrenean chain and continuously outcrops to the north of the AZ from Perpignan to the Basque Country. It is essentially composed of Mesozoic sediments associated with Paleozoic basement massifs (North Pyrenean massifs) and results from the inversion and northward thrusting of the basins formed during the Cretaceous rifting phase. The geology of the NPZ is unique in the world and of major interest for the study of the formation of passive continental margins and, in particular, for better constraining the thermal conditions of crustal thinning. The NPZ is the result of the inversion of extensional and transcurrent structures distributed along the Iberian–Eurasian plate boundary. Along the Iberia–Eurasia boundary itself, the Basque–Cantabrian basin was connected to the North Pyrenean basins (future NPZ). The evolution of the Pyrenean smooth‐slope basins contrasts with brittle‐dominated models of crustal thinnings, as exemplified along the Iberian–Newfoundland passive margins.
Rifting and continental break-up are fundamental tectonic processes, the understanding of which is of prime importance. However, the vast temporal and spatial scales involved pose major limitations to researchers. Analogue tectonic modelling represents a great means to mitigate these limitations, but studying internal deformation in lithospheric-scale models remains a challenge. We therefore present a novel method for lithospheric-scale rifting models that are uniquely monitored in an X-ray CT-scanner. CT-scanning, combined with digital image correlation (DIC) techniques, provides unparalleled insights into model deformation. Our models show that the degree of coupling between competent lithospheric layers, which are separated by a weak lower crustal layer, strongly impacts rift system development. Low coupling isolates the upper crust from the upper lithospheric mantle layer below, preventing an efficient transfer of deformation between both layers. By contrast, fast rifting increases coupling, so that deformation in the mantle is efficiently transferred to the upper crust, inducing either a symmetric or asymmetric (double) rift system. The observation that asymmetric deformation can initiate during the earliest rifting stages challenges the two-phase scenario involving initial symmetric rifting, prior to subsequent asymmetric rifting. Oblique divergence leads to en echelon graben arrangements, and seemingly delays break-up, somewhat in contradiction to concepts of oblique divergence promoting break-up. These insights provide an incentive to further run lithsospheric-scale rifting models, and to apply advanced monitoring techniques to extract as much information as possible from these. There is indeed a broad range of opportunities for follow-up studies within and beyond the field of rift tectonics.
Basin inversion involves the reversal of subsidence in a basin due to compressional tectonic forces, leading to uplift of the basin’s sedimentary infill. A thorough understanding of basin inversion is of great importance for scientific, societal and economic reasons. Analogue tectonic modelling forms a key part our efforts to improve our understanding of basin inversion processes, and researchers have conducted numerous studies on this topic. In this review paper we recap the advances in knowledge of basin inversion tectonics acquired through analogue modelling studies, providing an up-to-date summary of the state of analogue modelling of basin inversion. We describe the different definitions of basin inversion that are being applied by researchers, why basin inversion has been historically an important research topic, and what the general mechanics involved in basin inversion are. We subsequently treat the wide range of different experimental approaches used for basin inversion modelling, with attention to the various materials, set-ups and techniques used for monitoring and analysing the model results. Our new systematic overviews of generalized results reveal the diversity of model results, depending greatly on the chosen set-up, model layering and (oblique) kinematics of inversion, as well as 3D along-strike structural and kinematic variations in the system. We show how analogue modelling results are in good agreement with numerical models, and how these results help to better understand natural examples of basin inversion. In addition to reviewing the past efforts in the field of analogue modelling, we also shed light on future modelling challenges and identify a number of opportunities for follow-up research. These include the testing of force-boundary conditions, adding geological processes such as sedimentation, transport and erosion, applying state-of-the-art modelling and quantification techniques, and establishing best modelling practices. We also suggest expanding the scope of basin inversion modelling beyond the traditional upper crustal "North Sea style" of inversion, which may contribute to the on-going search for clean energy resources. It follows that basin inversion modelling can bring valuable new insights, providing a great incentive to continue our efforts in this field. We therefore hope that this review paper will form an inspiration for future analogue modelling studies of basin inversion.
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