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National audience; This study focuses on breccias, widely developed in the Bas Agly syncline at the LateJurassic/Early Cretaceous boundary. Both their age and formation processes aredebated and remained hypothetical until today.According to our detailed sedimentological study, the breccia localized in the LateJurassic are spatially associated with large-throw normal faults and show a clearsedimentary character. They result from the creation of a steep topography thatbecomes unstable, producing major rockfalls. The studied breccias, are characterizedby poorly sorted polygenic deposits of pebbles to boulders composed of highly angularpluri-millimetric to pluri-metric carbonate clasts. A lateral evolution is observed, withpebble-size clasts found near the normal fault and boulder-size clasts away from thefault. This evolution is related to the rockfall process as the total kinetic energy acquiredby the small clasts during the fall is lower than that acquired by the bigger ones; as aresult, the latter are able to travel farther. These breccias are related to a first stage ofextension during the Late Jurassic and marks the beginning of the Early Cretaceousextension. However, the heterogeneity and complexity of the structure of carbonatebreccias require a detailed characterization of both their petrographic evolution anddiagenetic paleoenvironment in order to confirm our sedimentological model.Based on observations under S.E.M, polarized-light and fluorescence microscopy adetailed inventory of the diagenetic phases has been performed. From these analyses, adiagenetic sequence and a chronology of the cements have been reconstructed, usingprinciples of overlapping, superposition and inclusion. The oxygen and carbon isotopiccompositions of some cements and matrices of these breccias allowed to specify thediagenetic environments.The occurrence of metamorphic minerals overprinting the latest phase of calcitecementation strongly suggests that the breccia deposited prior to the Albo-Cenomanianregional metamorphic phase in contrast to previous stratigraphic attributions (Eoceneage) and support our interpretation of an interstratified sedimentary breccia of LateJurassic age. Thus, it is crucial to know the real age of these rocks. In order to solve thisissue, we initiated a geochronological study, using in-situ U-Pb dating by LA-ICP-MSand focusing on the carbonate matrix of the breccias. This approach has provensuccessful and yielded ages consistent with the proposed depositional environment.

International audience; Sedimentary breccias formed during extensional tectonics are spatially associated with large-throw normal faults. They result from the creation of a steep topography that becomes unstable, producing major rockfalls. The studied breccias, in Crete and in the Pyrenees, are up to 300 meters thick and are characterized by poorly sorted polygenic deposits of pebbles to boulders composed of highly angular plurimillimetric to plurimetric carbonate clasts. A lateral evolution is observed, with pebble-size clasts found near the normal fault and boulder-size clasts away from the fault. This evolution is related to the rockfall process as the total kinetic energy acquired by the small clasts during the fall is lower than that acquired by the bigger ones; as a result, the latter are able to travel farther. Interestingly, the fact that the smallest clasts are proximal while the bigger ones are more distal is contrary to the distribution found in alluvial fan systems, making it possible to differentiate from one another. The studied breccias commonly show disorganized layers and/or no noticeable layering across large distances. We interpret this feature as related to the movement on the normal fault, which progressively tilts the breccia layers and favours their gliding along the slope. Gliding is an important internal process to take into account in rockfall systems because it may disorganize the layering, create specific geometries like onlap around olistoliths, and produce deformation inside the breccia layers; the latter feature could be mistakenly interpreted as resulting from post-deposition regional deformation.According to our observations, active normal faults with large throws provide the conditions for the formation and preservation of great volumes of sedimentary breccias through the following processes: i) footwall uplift, creating a pronounced topography with steep slopes, giving rise to major rockfalls, ii) hangingwall rapid subsidence, which allows the accumulation and preservation of the breccias without clast reworking by drainage systems. The latter is reinforced by the fact that, during the early stages of extension, the main watersheds point in a direction opposite to the fault slope whereas only small, discontinuously distributed watersheds flow in the direction of the fault slope. Upon ongoing extension, the size of these small watersheds increase. At one point, the sedimentary flow coming from these watersheds becomes more important than rockfall processes. Part of the breccia body is then eroded, reworked, and replaced by conglomerates of an alluvial fan deposited unconformably above the breccias.Summing up, sedimentary breccias are readily formed as thick syn-tectonic deposits during early stages of extensional basin development. Thus, they may be considered as a typical lithology, and a marker, of continental extension.

International audience; While several tectonic models are proposed to explain the formation of extensive basins and passive margins(simple shear, detachment, mantle exhumation .... ), a single thermal model (McKenzie, 1978), as a kind ofdogma, is used to understanding and modeling the formation and evolution of sedimentary basins. The studyof the thermal evolution, coupled with other tectonic models, and its consequences have never been reallystudied in detail. Petrological changes, related to temperature evolution, modify rock density and then thesubsidence history of the basin.Recent studies of continental passive margins collectively describe a great variety of processes accountingfor the extreme thinning of the continental crust. Among all the parameters that may act during crustalstretching, the thermal state of the system and the temporal evolution of the heat distribution during thinningappear of major importance.Constrained by the new field data from the north Pyrenean basins about thermal evolution of early marginformation, we explore effect of different thermal evolution on petrological changes and their consequenceson the geophysical signature of rifted zones associated to different thermal evolution and the consequenceson the subsidence of the basins. We will also present numerical models quantifying mineralogical andphysical changes inside the whole lithosphere during rifting processes. In the light of these models, wediscuss the consequences of different thermal evolution on the subsidence processes as well as ongravimetric and seismic velocities signature of passive margins.We are able to distinguish two types of margins according to their thermal evolution:- An Alpine-type basin in which the temperature rise is 50 to 100 Ma older than the tectonic extension,leading to the "cold" opening of the ocean.- A Pyrenean type basin in which temperature changes are synchronous with basin formation, leading to acrustal boudinage and to the formation of a “anomalous” geophysical layer at the OCT

International audience; The ”Landes-Parentis area” (LPA) is located at the transition between the eastern end of the abyssal plain of the Bay of Biscay, the Aquitaine basin to the east and the highly inverted Basque-Cantabrian basin to the south. It includes the Meso-Cenozoic Parentis basin (PB) bordered to the south by a Paleozoic high named Landes High (LH). The purpose of the study is to highlight the deformation of the Landes-Parentis area during extension from the end of Jurassic to the early Cretaceous, and then during inversion from the Upper Cretaceous onward.To understand this evolution, we analyzed ten regional 2D seismic lines through the LPA from the coast to the oceanic crust and from the LH to the Armorican margin. We mapped the main structures and stratigraphic unconformities. Well data from the PB has been used for the age dating of the different unconformities.The maps show that the Mesozoic cover observed in the PB extends to the foot of the con- tinental slope while all the Jurassic and Lower Cretaceous series are absent on the LH. The LPA continental slope is structured with west dipping normal fault. Further east, the contact area between PB and LH is particularly complex. Indeed, the PB presents an asymmetry between a gentle south dipping northern flank and a steep and faulted southern flank in a direct contact with LH. The LPA is also crossed by a NW-SE to NNW-SSE oriented, sinistral accident: the Landes transfer zone (LTZ). This transfer zone seems to continue in the LH by a set of NW-SE normal faults.East of this accident, the southern flank of the BP shows EW-oriented anticlines structures, attributed to salt ripples. The structural style shows normal faults inverted during the Tertiary and ramp anticlines. To the west, the southern flank presents two tilted blocks limited by EW- oriented crustal faults with a north-dipping normal movement. These faults affect the Triassic to Lower Cretaceous sedimentary series. They are sealed by the Upper Cretaceous to Tertiary sedimentary deposits. The structural scheme is mainly extensive.These results show that the NW-SE direction of the LPA, oblique with respect to the main NNE-SSW transfer zones of the Pyrenees and the lateral partitioning of the local deformation are probably strongly influenced by the presence of Landes High that play the role of a rigid block.

International audience; The North Aquitaine continental shelf is a key sector to understand the deformation of this shelf related to the rifting events of the Bay of Biscay and the orogenic Pyrenean phases that may help to understand the role of the inheritance on present day structures.We propose a new analysis of the onshore-offshore tectonic structure of the Charente Region and the North Aquitaine shelf1 based on i) aerial photographies and field measurements along the coast of the Oleron and Ré Islands and the Charente River area, and ii) a newly acquired very high resolution offshore seismic survey2. Offshore we confirm the presence of a large Mesozoic synclinal with an NW-SE axis dipping to the SE and of NE-SW lineaments segmenting the shelf. The Mesozoic sedimentary cover exhibits faults and folds with major faults showing more than 10m large throws. These faults are mainly oriented EW near the coast and NW-SE further off- shore. The same directions of faults were also observed in the Cenozoic formations of the South Brittany shelf. Onshore, the analysis of field measurements and aerial photographies show the extensive occurrence of normal faults oriented in an EW direction and strike slip faults oriented in NW-SE and NE-SW directions associated with folds.This preliminary structural study provides information on the distribution of structures, style and timing of deformations in the Charentes area induced both by the Biscay rifting, with creation of extensive structures, and/or the orogenic Pyrenean phase that is certainly associated with strike-slip displacement.

International audience; While several tectonic models (e.g., simple shear, detachment or mantle exhumation) are proposed to explain theformation of extensive basins and passive margins; a single thermal model (McKenzie, 1978), as a kind of dogma,is used to model the formation and evolution of sedimentary basins. The thermal evolution of such basins, coupledwith other tectonic models, have been scarcely studied in detail. For instances, petrological changes (i.e. phasetranisitions), related to temperature changes, affect rock density and thus influence the subsidence history of thebasin. Recent studies of continental passive margins collectively describe a great number of processes accountingfor the extreme thinning of the continental crust. Among all the parameters that may act during crustal stretching,the thermal state of the system and the temporal evolution of the heat distribution during thinning appear of majorimportance.We explore the effect of different thermal evolution models on petrological changes and their consequences on thegeophysical signature of rifted zones.We will present computed geodynamic models quantifying mineralogical and physical changes in the lithosphereduring rifting processes and early margin formation. In the light of these high temperature evolution modelssupported by new field data from the north Pyrenean basins, we discuss the effect on subsidence as well as ongravimetric and seismic velocities signatures of passive margins.Consequently, we are able to distinguish two types of margins according to their thermal evolution:- An Alpine-type basin in which the temperature increase is 50 to 100 Ma older than the tectonic extension,leading to the "cold" opening of the ocean.- A Pyrenean type basin where heating is coincident with basin formation, leading to a crustal boudinage andformation of an “anomalous” geophysical layer at the OCT

Analogue modelling has proven to be an essential tool for the study and analysis of the mechanisms involved in tectonic processes. Applied to salt tectonics, analogue modelling has been used to understand the mechanisms that trigger the onset of diapirs and the evolution of diapiric structures and minibasins. Analogue modelling has also been applied to analyse the impact of the progradation of sedimentary systems above a ductile layer, representing the source of diapirs. However, these models did not consider ongoing tectonic processes during progradation. To analyse how extension and sedimentary progradation influence on the formation of diapiric structures and their geometries, we present models composed of a mildly extension followed by post-extension period. Each model includes a particular sedimentary pattern: homogeneous sedimentation during extension and post-extension, homogeneous sedimentation during extension followed by prograding sedimentation during post-extension and prograding sedimentation during both extension and post-extension. Proximal high sedimentation rates enhance the mobilization of ductile material towards growing diapirs, resulting well-developed passive diapirs. Diapirs from distal domain of the model with post-extension progradation show silicone extrusions, that are caused by the decreased sedimentation rate associated to the progradation. By contrast, reduced sedimentation in the distal part of the model with syn- and post-extension progradation (3.5 times smaller than in the proximal domain) causes a limited migration of the silicone and hampers the transition from reactive diapirs to active and passive diapirs. These models show that the ratio between diapir growth and sedimentation rate, the time of the onset of the progradation and the relative thickness of the sedimentary cover beneath the prograding system have a clear impact on the final diapiric geometries. Additionally, we present two models with increasing amounts of shortening (6% and 10%). These models show that the presence and location of diapirs clearly controls the distribution of the deformation associated with the inversion, primarily affecting the post-diapiric layers in the vicinities of the salt structures whereas very little deformation occurs away from diapirs. This deformation pattern is observed in the Early to Middle Jurassic Tazoult salt wall and Azourki diapir of the Central High Atlas (Morocco). These structures show that the deformation associated with the Alpine orogeny is focused on the sedimentary units fossilizing the salt structures and mainly localised above them. The presented results provide key information that can be applied to other diapiric structures of the Central High Atlas diapiric basin and similar examples elsewhere., This study was part of a collaborative research project funded by Statoil Research Centre, Bergen (Norway). Additional funding by the CSIC-FSE 2007-2013 JAE-Doc postdoctoral research contract (E.S.), the projects Intramural Especial (CSIC 201330E030) and MITE (CGL 2014-59516). and by the Grup Consolidat de Recerca >Geologia Sedimentària> de la Generalitat de Catalunya (2014GSR251). We are grateful to Statoil for its support and permission to publish this study.

International audience; Many large-scale dynamic processes, from continental rifting to plate subduction, are intimately linked tometamorphic reactions. This close relation between geodynamic processes and metamorphic reactions is, inspite of appearances, yet poorly understood. For example, during extension processes, rocks will be exposed toimportant temperature, pressures and stress changes. Meanwhile less attention has been paid to other importantaspects of the metamorphic processes. When reacting rocks expand and contract, density and volume changes willset up in the surrounding material.While several tectonic models are proposed to explain the formation of extensive basins and passive margins (simple shear detachment mantle exhumation .... ) a single thermal model (McKenzie, 1978), as a kind of dogma, isused to understanding and modeling the formation and evolution of sedimentary basins. The study of the thermalevolution, coupled with other tectonic models, and its consequences have never been studied in detail, although thedifferences may be significant. And it is clear that the petrological changes associated with changes in temperatureconditions, influence changes reliefs.Constrained by the new field data of north Pyrenean basins on thermal evolution of pre-rift and syn-rift sediments,we explore the petrological changes associated to different thermal evolution and the consequences on thesubsidence of the basins. We will also present numerical models quantifying mineralogical and physical changesinside the whole lithosphere during rifting processes. In the light of these models, we discuss the consequences ofdifferent thermal evolution on the subsidence processes as well as on gravimetry and seismic velocities signatureof passive margins.We are able to distinguish two types of margins according to their thermal evolution:- An Alpine-type basin in which the temperature rise is 50 to 100 Ma older than the tectonic extension, leading tothe "cold" opening of the ocean.- A Pyrenean type basin in which temperature changes are synchronous with basin formation, leading to a crustalboudignage and to the formation of a “anomalous” geophysical layer at the OCT

National audience; s’exprime sous la forme de failles normales. Dans la croûtesupérieure fragile la géométrie des failles normales est liée à larhéologie des séries impliquées, et aux transferts de matières (érosion- sédimentation). Il est classique de considérer les géométriescomplexes de failles normales avec changement de pendage àl’échelle de la croûte par contre la variabilité de la géométriedes failles normales dans la partie très supérieure de la croûteet l’implication sur le régime tectonique est encore très peu priseen compte. En effet, d’un côté, les variations de rhéologie desséries impliquées peuvent engendrer des variations de comportementmécanique des roches et la création de potentiels niveauxde décollement, d’un autre côté les transferts de matières et lasédimentation syndéformation peut modifier les forces appliquéesau système durant la déformation et modifier la géométrie desstructures.On se propose ici à l’aide d’une série de modèles analogiquesd’étudier le rôle de la stratigraphie mécanique et de la sédimentationsur la géométrie des failles normales et des structures associées.On étudie aussi de façon détaillée les géométries des faillesnormales et des structures, à proximité immédiate de ces faillesnormales afin de mieux appréhender la rhéologie des séries impliquéeset notamment la présence de niveau de découplage defaible épaisseur.Les résultats permettent de suggérer (i) que les failles normalesaugmentent de pendage et deviennent quasi-verticales voire faillesinverses et ce en régime uniquement extensif à cause de la sédimentation; (2) que les failles normales diminuent de pendageet deviennent quasi-horizontales, avec création de pli forcé dansles séries du compartiment supérieur de la faille et ce en régimeuniquement extensif à cause de la présence d’un petit niveau incompétent.Ainsi les structures complexes de faille normale peuvent être souventinterprétée uniquement en extension pure sans faire appel nià du décrochement ni à inversion

National audience; La déformation extensive et la géométrie des failles normalesdans les bassins sédimentaires sont influencées par la stratigraphiemécanique. Les roches compétentes accommodent la déformationde façon fragile, tandis que les roches incompétentes accommodentla déformation de façon plus ductile. En contexte extensif àfaible quantité de déformation, la géométrie d’une faille normaleest alors contrôlée par la rhéologie des roches de la pile stratigraphiquequ’elle affecte. L’impact de la stratigraphie mécaniquesur le développement/dimensionnement des failles a jusqu’alorsété peu étudié.Afin d’apporter de nouvelles contraintes sur ce thème, cette étudese base sur une approche multi- échelle comprenant 1/ des donnéesacquises lors d’une campagne de terrain en Espagne, 2/l’interprétation de deux blocs de sismique 3D (Angola, Nigéria)et 3/ des résultats d’expériences de modélisation analogique. Lasynthèse des données sur un diagramme log/log amène à proposerune loi de dimensionnement selon laquelle la longueur du plat (Lp)est sensiblement égale à l’épaisseur de la formation incompétente(Ed) dans laquelle elle se met en place (Lp=kEd). Le facteur kreprésente alors les paramètres mécaniques et contextuels faisantvarier le rapport Lp/Ed (compaction, pression fluide, taux de déformation,...). De plus, sur la base de cartes de rejet, cette étudedémontre l’implication de la présence des plats sur la distributionlatérale et verticale du rejet le long du plan de faille. Il apparaitque le rejet d’un segment de faille compris entre deux plats estsystématiquement moins fort. Enfin, cette relation directe entrerejet et plat engendre la formation de structures comme des pliset/ou des failles antithétiques. L’observation de ces géométries,n’étant pas caractéristiques d’un domaine extensif, peut alorsmener à de fausses interprétations quant à la nature des faillesqui les engendrent - failles inverses ou décrochantes - ou sur lanature de la déformation - décrochement ou inversion.Au final, cette étude propose un modèle de croissance de faillesdans un volume de roches dominé par des alternances rhéologiquesfragile/ductile avec Lp/Ed =1. Le diagramme log/log présenteplusieurs domaines : l’un à déformation purement fragile (Lp/Ed< > 1), avec formation de plats

National audience; Les brèches de la zone nord pyrénéenne sont un des témoinsde l’histoire géodynamique des Pyrénées. Les affleurements debrèches sont nombreux dans cette zone et il existe une variété importanteen termes de faciès et de géométries. Les différents typesd’associations faciès-géométries sont dépendant du processus deformation (tels que des processus sédimentaires, tectoniques ouencore de fracturation hydraulique) et constituent ainsi des indicesdu contexte géodynamique local. Ainsi, il convient de définir quelssont les critères discriminants dans la caractérisation des différentsfaciès de brèches afin de déterminer quelles sont les origines de laformation des brèches pyrénéennes. Cette étude porte sur un desfaciès de brèches présent dans la région de Latour-de-France : lesbrèches dite Éocène (eBr). Ces brèches (eBr) se retrouvent sur lesbordures des synclinaux du Bas Agly et Saint Paul de Fenouillet,ainsi que coincées dans le Massif de l’Agly. Cette étude focaliséesur la carrière de Roc Pointu sur le flanc sud du synclinal du BasAgly entre Cases de Pène et Estagel a permis de confirmer que lesbrèches de type eBr, considérées comme sédimentaires et Eocènesdonc syn-compression alpine (Mattauer et Proust, 1962 ; Bergeret al., 1993), sont effectivement d’origine sédimentaire mais sesont mises en place antérieurement à l’Albo-Cénomanien. La fortereprésentativité des brèches de type eBr dans la zone d’étude indiqueraitdonc, qu’à l’Albo-Cénomanien, de fortes pentes jalonnaientles zones actuelles synclinales et que leur déstabilisationserait à l’origine de la mise en place des brèches sur les formationsante-albiennes. Dans la mesure où cette époque correspondà une phase d’extension (plus ou moins décrochante), l’origine deces escarpements est à relier à des failles normales (plus ou moinsdécrochantes) qui formaient les bordures des bassins.

National audience; Many large-scale dynamic processes, from continental riftingto plate subduction, are intimately linked to metamorphic reactions.This close relation between geodynamic processes andmetamorphic reactions is, in spite of appearances, yet poorly understood.For example, during extension processes, rocks will beexposed to important temperature, pressures and stress changes.Meanwhile less attention has been paid to other important aspectsof the metamorphic processes. When reacting rocks expand andcontract, density and volume changes will set up in the surroundingmaterial.While several tectonic models are proposed to explain the formationof extensive basins and passive margins ( simple sheardetachment mantle exhumation .... ) a single thermal model(McKenzie, 1978), as a kind of dogma, is used to understandingand modeling the formation and evolution of sedimentary basins.The study of the thermal evolution, coupled with other tectonicmodels, and its consequences have never been studied in detail,although the differences may be significant. And it is clear thatthe petrological changes associated with changes in temperatureconditions, influence changes reliefs.Constrained by the new field data of north Pyrenean basins onthermal evolution of pre-rift and syn-rift sediments, we explorethe petrological changes associated to different thermal evolutionand the consequences on the subsidence of the basins. We willalso present numerical models quantifying mineralogical and physicalchanges inside the whole lithosphere during rifting processes.In the light of these models, we discuss the consequences of differentthermal evolution on the subsidence processes as well as ongravimetry and seismic velocities signature of passive margins.

National audience; This study is based on a coupled basin infilling study and alandforms analysis of the Lake Albert Rift located at the northernpart of the western branch of the East African Rift.The basin infilling study is based on both subsurface data andoutcrops analysis. The objective was to (1) actualize age model,(2) to reconstruct the 3D architecture of the rift using sequencestratigraphy correlations and seismic data interpretation, (3) tocharacterize the deformation and its changes through times and(4) to quantify the accommodation for several time intervals. Theinfilling essentially consists of isopach fault-bounded units composedof lacustrine deposits wherein were characterized two majorunconformities dated at 6.2 Ma (Uppermost Miocene) and2.7 Ma (Pliocene-Pleistocene boundary), coeval with major subsidenceand climatic changes.The landforms analysis is based on the characterization and relativedating of Ugandan landforms which consist of stepped planationsurfaces and incised valleys. We here proposed a seven-stepsreconstruction of the deformation-erosion-sedimentation relationshipsof the Lake Albert Basin and its catchments:- 55-45 Ma: formation of laterites corresponding to the AfricanSurface during the very humid period of the Lower-Middle Eocene;- 45-22: stripping of the African Surface in response of the beginningof the East-African Dome uplift and formation of a pediplainwhich associated base level is the Atlantic Ocean;- 17-2.5 Ma: Initiation of the Lake Albert Basin around 17 Ma andcreation of local base levels (Lake Albert, Edward and George) onwhich three pediplains tend to adapt;- 18-16 Ma to 6.2 Ma: ”Flexural” stage (subsidence rate: 150-200 m/Ma; sedimentation rate 1.3 km3/Ma between 17 and 12Ma and 0.6 km3/Ma from 12 to 6 Ma) – depocenters location(southern part of Lake Albert Basin) poorly controlled by fault;- 6.2 Ma to 2.5 Ma: Rift stage 1 (subsidence rate: > 500m/Maup to 600-800 m/Ma; sedimentation rate: 2.4 km3/Ma) – Riftingclimax;- 2.5-0.4 Ma: uplift of the Ruwenzori Mountains and shifting froman alluvial system to a network of bedrock river incision – RiftStage 2 (subsidence rate: 450 to 250 m/Ma; sedimentation rate:1.5 km3/Ma);- 0.4-0 Ma: long wavelength downwarping of the Tanzanian Craton,initiation of the Lake Victoria trough, drainage network inversionand uplift of the present-day Ugandan escarpment (normalfaulting motion of the border faults) with formation of perchedvalleys associated to the Lower Pleistocene (2.5-0.4 Ma) riversnetwork.The sediment budget is successful with, between 17 and 2.5 Ma,an excess of 16 % of upstream eroded material compared to thesediment volume deposited that can be explained by the chemicalerosion prevailing at this period in Central Africa. The significant(60%) opposite difference between 2.7 and 0 Ma may be the consequenceof a high sediment supply resulting from the erosion ofthe uplifted Ruwenzori Mountains.

GeoMod 2016 conference Montpellier, France | 17–20 October 2016, Analogue modelling has been previously applied to the analysis of the impact of the progradation of a sedimentary system above a ductile layer (McClay et al., 1998). Commonly, diapiric architecture increases in complexity with: (i) lobe progradation, where the radial shape of the prograding system causes a complex network of polygonal or circular depocenters separated by salt ridges (Gaullier and Vendeville, 2005); (ii) basement topography beneath the ductile layer (Ge et al., 1997); and (iii) the confluence of two sedimentary wedges (Guerra and Underhill, 2012). The outstanding results obtained in all these models, however, did not consider ongoing tectonic processes during diapirism. We present 2 models with two phases (extension and post-extension phases) with different timing of progradation of sedimentary wedge in order to analyse how the time relationship between extension and sedimentary progradation control the formation of diapiric structures and their geometries.

International audience; The Pyrenean belt is resulting in the inversion of several lower Cretaceous basins, separating the Iberia micro-platefrom the Eurasia plate. The eat-west oriented basins are well known for their high-temperature metamorphismsynchronous of the last deposits during Aptian-Albian times.For the first time, we present a combined sedimentological and thermal study of three north pyrenean basins(Boucheville, St Paul-de-Fenouillet and Bas-Agly). With the help of detailed stratigraphic logs of each basin,we propose restored cross-sections for the whole area. North-south sections across Boucheville and St Paul-de-Fenouillet basins show that theses basins have large asymmetrical structure. The Boucheville basin is a largeanticline bordered by two isoclinal syncline highly skewed, while the St Paul-de-Fenouillet one is a uniquesyncline.Detailed sedimentalogical observations show common features for these basins: deposits of white limestones andbreccias during the Jurassic time following by black sandstones with a calcareous matrix of lower Cretaceous age.On one hand, Jurassic limestones were deposited on a shelf environment and their thickness is homogeneous allover each basin. On the other hand, sandstones deposits seem to occur at greater depths during the Albian timeand are displaying asymmetrical north-south variation of their thickness.The quantification of the temperature overprint occurred in the basin was done using the graphitisation of thecarbonaceous material, and was measured by RAMAN spectroscopy (Lahfid et al. 2010). Despite their similardeposits, the mapping of the temperature-peak inside the three basins show contrasted thermal evolution. Then wedocument a lower temperature overprint around 150-200°C in the northern basin {St Paul-de-Fenouillet) while thehighest overprint up to 600°C has been reached in the southern basin (Boucheville) in which diopside - scapoliteand also probably olivine are occurring.These three north-pyrenean basin turn out to be good places where to study the evolution of passive marginanalogue and also to be a good example where the sediments were metamorphosed during the basin set up.

International audience; Volcaniclastic sediments, often under-studied, constitute an important part of the global sedimentary record, bothin marine and continental environments. These sediments are of particular importance in order to constrain the ageof sedimentation, particularly in series where interbedded lava flow are absent. Volcaniclastics sediments are alsoused in order to constrain the duration of the volcanic activity and to link volcanism with a specific geodynamiccontext. To demonstrate that volcanism and sedimentation were contemporaneous in a given basin, it is crucial todetermine to which extent volcaniclasts present in the volcaniclastic sediments have been reworked. However, thisdetermination is notoriously difficult.As a case study, we characterized the Triassic volcaniclastic series from the Luang Prabang Basin, Laos,using coupled sedimentological and geochronological analyses. Sedimentological and petrographical analysesshow a wild range of depositional environments (alluvial fan, braided river and alluvial plain) and evidence forreworking of the volcaniclastics in each of the corresponding deposits. U-Pb geochronology conducted on zircongrains extracted from the volcaniclastic samples of known stratigraphic position indicates that the maximumdepositional ages get younger together with the sedimentary succession. This good correlation between absoluteages and stratigraphy demonstrates that, despite evidences of reworking, the volcaniclasts were produced, at leastto some extent, contemporaneously with sedimentation. Then, in this specific example, the uncertainties obtainedfrom the U-Pb ages can be used to indicate the ‘reworking time scale’, defined as the difference between theage of volcaniclast production and the depositional age of its host strata. Short reworking time scales, of ca. 1Ma, one order of magnitude smaller than the total duration of the sedimentary record reveal that volcanism andsedimentation were contemporaneous. The use of coupled sedimentological and geochronological analyses maythus allow to determine the duration of volcanic activity even in the absence of volcanic deposits. Constraining thereworking time scales is useful to describe volcaniclastics deposits in which the volcaniclasts were reworked

International audience; Many large-scale dynamic processes, from continental rifting to plate subduction, are intimately linked to metamorphicreactions. This close relation between geodynamic processes and metamorphic reactions is, in spite ofappearances, yet poorly understood. For example, during extension processes, rocks will be exposed to importanttemperature, pressures and stress changes. Meanwhile less attention has been paid to other important aspects ofthe metamorphic processes. When reacting rocks expand and contract, density and volume changes will set up inthe surrounding material.While several tectonic models are proposed to explain the formation of extensive basins and passive margins (simple shear detachment mantle exhumation .... ) a single thermal model (McKenzie , 1978), as a dogma, is usedto understanding and modeling the formation and evolution of sedimentary basins . This model is based on theassumption that the extension is only by pure shear and it is instantaneous. Under this approach, the sedimentarydeposits occur in two stages. i) A short step , 1 to 10 Ma , controlled by tectonics. ii) A longer step , at least 50 Maas a result of the thermal evolution of the lithosphere.However, most stratigraphic data indicate that less thermal model can account for documented vertical movements.The study of the thermal evolution , coupled with other tectonic models , and its consequences have never beenstudied in detail , although the differences may be significant and it is clear that the petrological changes associatedwith changes in temperature conditions , influence changes reliefs.In addition, it seems that the relationship between basin formation and thermal evolution is not always the same:- Sometimes the temperature rise above 50 to 100 Ma tectonic extension. In the Alps, a significant rise in geothermalgradient Permo -Triassic followed by a "cold" extension , leading to the opening of the Ligurian- Piedmontocean, from the Middle Jurassic .- Other examples show that temperature changes are synchronous with basin formation . For example, extensiveponds Cretaceous North Pyrenean clearly indicate that the "cooking" of contemporary sediment deposit.In the light of new models, we discuss the consequences of the formation of LP-granulites during rifting on deformationand the subsidence processes.

International audience; Fold and thrust belts are influenced by the presence of decollement levels,as well as the amount of shortening and synkinematic sedimentation.These parameters are studied at the scale of a thrust belt usinga field approach, combined with analogue and numerical modelling. Inthis study, we use analogue modelling to test the evolution of a singlestructure during sedimentation in a domain containing three prekinematicdecollement levels. The development of this structure in the analogueexperiments shows that the expression of the deformation is stronglydependent on sedimentation rate : (i) the structure propagates forwardin an overall asymmetric shape if the sedimentation rate is slower thanthe uplift velocity, or (ii) the structure grows vertically and its vergencechanges at the surface if the sedimentation rate is similar to the upliftvelocity, or (iii) the structure grows vertically with a double vergence atthe surface and at depth if the sedimentation rate is higher than the upliftvelocity. The results of the experiments are compared with structures inthe Subandean thrust belt to aid the interpretation of poor seismic data.

International audience; Analogue sandbox models have been set up to study the impact of synkinematicdeposits on the geometry and evolution of single thrusts andfolds according to different sedimentation modes (a slow or rapid sedimentationrate that is constant or changing in space and time) and rheologicalprofiles (thin or thick sedimentary series, with a basal décollementlevel or not). A first series of experiments documents the influenceof synkinematic deposits according to their sedimentation rate and therheology of the prekinematic materials. A second series investigates theinfluence of changes in the sedimentation rate through time. A third oneconsiders the influence of changes in the sedimentation rate in space.All these experiments suggest that the geometry and evolution of singlecompressive growth structures vary according to the sedimentation rate.The number and dip of their frontal thrust segments change with the ratioR between the sedimentation rate (Vsed) at the footwall of the faultsand the uplift rate (Vupl) of their hanging wall. The latter is then more orless uplifted depending on the dip of the thrusts. As a result, the overallstructure has either a fault-bend fold or a fault-propagation fold geometry.Those rules are verified when the ratio R (Vsed/Vupl) changes inspace or through time. In addition, the rheological profile of the modelsalso affects the geometry and evolution of compressive growth structures.Their structural style, as well as the synsedimentary splitting andsteepening of the associated thrusts, varies according to the occurrenceand strength of the brittle and ductile layers.According to this modelling study, the ratio R (Vsed/Vupl) and itschanges in space and time, along with the rheology of the deformedmaterials, are key parameters to better understand the geometrical andkinematical complexities of natural growth thrusts and folds and to improvetheir interpretation.

International audience; Les bassins mésozoïques de la zone Nord-Pyrénéenne ont été mis enplace lors de l’extension entre les plaques Européenne et Ibérique àl’Albien. La partie sud de la ZNP a subi un métamorphisme HT/BPlié à cette extension. Ce métamorphisme Albien est observé dans lesbassins et dans les massifs cristallins nord-pyrénéens où il est associé àdes filons d’albitites et à du manteau exhumé.Deux campagnes de terrains ont été réalisées afin de cartographier etd’échantillonner une zone comprenant à la fois des bassins mésozoïques(Boucheville et Saint Paul de Fenouillet) et une zone de socle (massifde l’Agly).Une étude sédimentologique et structurale a permis de produire un logsynthétique du bassin de Boucheville et des coupes restaurées de lazone. Une coupe Nord-sud montre notamment que le bassin de Bouchevilleest un grand anticlinal bordé de deux synclinaux isoclinaux fortementasymétriques.Des mesures RAMAN sur matière organique ont été réalisées dans lebassin de Boucheville en cohérence avec le log afin d’obtenir une cartedes températures du métamorphisme Albien. Elles révèlent une fortehomogénéité des températures situées entre 500°C et 600°C. Enfin une étude pétrologique du massif de l’Agly a révélé la présencede deux phases de métamorphisme HT/BP, séparées par une phase d’exhumation.Les conditions mesurées sont de 2,7 - 3,5 kbar et 700 - 800°Cpour le premier événement et de 5,8 - 7 kbar et 750 - 825°C pour lesecond.Ces données combinées permettent de proposer un modèle d’évolutiontectono-sédimentaire et métamorphique de la zone pendant l’extensionAlbienne et posent des questions quant aux interactions qui peuventexister entre la mise en place d’un bassin et un métamorphisme de hautgrade en phase extensive.

International audience; Geometry of normal faults, within the sedimentary cover, may be influencedby different parameters such as the presence, position and efficiencyof décollement levels, the amount, direction and velocity of extension,and the rate of synkinematic sedimentation. These parametershave already been studied at different scales in field approach, analogueand numerical modelling. The effect of several décollement levels hasbeen studied at lithospheric scale to better understand the deformationprocesses between surface and depth. At the scale of single structure ina sedimentary basin, previous analogue modelling only studied the effectof a determined geometry of a fault on the synkinematic sedimentation.Here we used analogue modelling to analyse the 3D geometry of asingle structure in a domain with three prekinematic décollement levels,analogue of salt, shale or under-compacted level. These experiments resultin flat and ramp geometry in relation with décollement level andthe pattern of the deformation depends here mainly on the velocity andamount of extension. The results of the experiments were compared toseismic examples in order to better interpret typical fault setups. Oneof the key points is that the geometry of normal faults displays largevariations both in direction and dip, only in pure extensive regime, relatedto the presence of décollement levels, and not associated with anyglobal/regional variation of extension direction.

International audience; Lake Albert Basin is assumed to be a classical half-graben initiatedaround 10 Ma and oriented NNE-SSW, with a major northwesterlybounding fault located along the western Congolese shoreline (Ebinger,1989 ; Pickford & al., 1993).This study aims to characterize the relationships existing between deformation,erosion, and sedimentation of the rift through time by restoring(1) the timing and amplitude of vertical movements (subsidence, uplift),(2) the geometry and paleo-environmental evolution of the sedimentaryinfilling and (3) the geomorphological evolution of the surrounding areaand its associated erosion budget.Seismic data and outcrops studies suggest a much more complex historythan previously described. (1) The age model, mainly based on mammalfossils (Pickford et al., 1993 ; Van Damme and Pickford, 2003), isdebated, but the early stage of the rift is probably Early to Middle Miocene.(2) No half-graben geometry has been characterized : the infillingconsists of juxtaposed isopach tabular compartments with sharp thicknessesvariations along bounding faults, in response of either low rate extensional or combined strike-slip/extensional movements. The followingonshore-offshore evolution is proposed :- Middle Miocene (18-13Ma) to Late Miocene (7Ma) : low extension -low and slightly differential subsidence - deepening from fluvio-deltaicto deep lacustrine environments - first generation of pediments.- Late Miocene (7Ma) to Late Pliocene (3Ma) : combined strikeslip/extensional movements - homogenous and high subsidence - lacustrineclays interbedded with sandy flood-lobes - second generation ofpediments.- Late Pliocene (3Ma) to Early Pleistocene (2Ma) : Ruwenzori uplift- growth of the Ruwenzori Mountains (5000m) - high and slightly differentialsubsidence - deltaic to wave-dominated coast sandy deposits -pediments degradation by fluvial erosion.- Middle-Late Pleistocene : late regional uplift and tilting - drainage inversionand present-day scarp formation.

International audience

Indexación: Web of Science; Scielo ABSTRACT. The current paper analyzes the evolution of the Abanico Basin, in the Chilean Principal Cordillera in central Chile (33°-35°S). According to previous studies, the basin has been affected by two main deformational episodes: the first, related to extension, and the second, to partial basin inversion. Deposits of the Abanico Formation, Eocene-Oligocene, and the Farellones Formation, Early-Middle Miocene, represent these two deformational episodes, respectively. Studies of the basin deposits and the structural features show that the basin was asymmetric and that it developed two main depocenters. The eastern depocenter is deeper and was controlled by a west-dipping fault system (El Diablo Fault System) that formed its eastern border. We propose that the geometry of the basin and the magnitude of inversion were strongly influenced by the load generated by the thick volcanic and volcaniclastic pile that accumulated in the eastern depocenter. Through analogue modeling, we interpret that the Aconcagua fold-thrust belt was triggered at ~16 Ma by a shortcut thrust rooted in the El Diablo Fault System, which during inversion was blocked because of the high load exerted by the deposits of the Abanico and Farellones formations. In addition, the stratified Mesozoic succession that formed the eastern border of the basin allowed the propagation of the shortcut thrust along the ductile Oxfordian gypsum layer. This would have determined the east vergence of the fold-thrust belt. On the western side of the basin, the absence of weak layers prevented development of a west-vergent fold-thrust belt. Keywords: Andes, Abanico Basin, Tectonic inversion, Shortcut thrusts, Aconcagua fold-thrust belt. RESUMEN. El presente trabajo analiza la evolución de la cuenca Abanico, expuesta en la Cordillera Principal de Chile Central (33°-35°S). De acuerdo con estudios anteriores, la cuenca se ha visto afectada por dos grandes episodios de deformación: el primero se relaciona con extensión y el segundo con inversión parcial de la cuenca. Los depósitos de la Formación Abanico, Eoceno-Oligoceno, y de la Formación Farellones, Mioceno Temprano-Medio, respectivamente, representan estos dos episodios de deformación. Los estudios de los depósitos y sistemas estructurales de la cuenca, muestran que ésta fue asimétrica y se desarrolló con dos depocentros. El depocentro oriental es más profundo que el occidental, y fue controlado por un sistema de fallas de manteo hacia el oeste (Sistema de Fallas El Diablo). Este sistema de fallas formó el borde oriental de la cuenca. En este trabajo planteamos que la geometría de la cuenca y la magnitud de la inversión fueron fuertemente influenciadas por la carga asociada a la potente sucesión volcánica y volcanoclásticas acumulada en el depocentro oriental. A través de modelación analógica, interpretamos que la faja corrida y plegada de Aconcagua comenzó su desarrollo desde los ~16 Ma, por una falla de atajo enraizada en el Sistema de Fallas El Diablo. Durante la inversión de la cuenca, este sistema de fallas fue bloqueado debido a la alta carga ejercida por los depósitos de las formaciones Abanico y Farellones. Además, proponemos que la sucesión mesozoica estratificada que forma el borde oriental de la cuenca, permitió la propagación de las fallas inversas de atajo a lo largo capas dúctiles del Yeso Oxfordiano. Esto habría determinado la vergencia hacia el este de la faja corrida y plegada. En el lado occidental de la cuenca, la ausencia de capas frágiles impidió el desarrollo de una faja corrida y plegada. Palabras clave: Andes, Cuenca Abanico, Inversión tectónica, Fallas inversas de atajo, Faja corrida y plegada del Aconcagua.

International audience; The Luang Prabang Basin, located on the eastern margin of the Indochina block, is mainly composed of volcaniclasticcontinental deposits. The interpretation of U-Pb zircon geochronological dates shows that volcanism iscontemporaneous with the sedimentation during the Late Triassic (c.a. 225 to 215 Ma; Blanchard et al., 2013,J. Asian Earth Sci., 70-71; 8-26). At the same time, volcanism is also known along the Eastern margin of theIndochina block (present day Thailand).There are currently two main contrasting interpretations concerning the tectonic setting related to these volcanicevents: are they arc-related (e.g. Barr et al., 2006, J. Geol. Soc. London, 163; 1037-1046) or post collisional (e.g.Srichan et al., 2009, Island Arc, 18; 32-51)? We have performed geochemical analysis on both sedimentary andvolcanic rocks of the Luang Prabang Basin in order to evaluate the relationships between the volcanic events andto propose a geodynamic interpretation.The geochemical characteristics of the Luang Prabang Late Triassic volcaniclastic and volcanic rocks arecompatible with a volcanic arc setting. The confrontation of these results with the stratigraphic evolution of theeastern margin of the Indochina block leads to reconsider the Late Triassic to Jurassic geodynamic evolutionof this area. Arc-related volcanism seems to occur during nearly the whole Triassic, implying a subduction ofthe Paleotethys beneath the Indochina block. As the stratigraphic record of north-eastern Thailand and westernMyanmar shows an important stratigraphic gap spanning from the Early to the Middle Jurassic, the collisionbetween the Indochina and the Sibumasu blocks likely occurred at that period.