Evolution of a low convergence collisional orogen: a review of Pyrenean orogenesis

The Pyrenees is a collisional orogen built by inversion of an immature rift system during convergence of the Iberian and European plates from Late Cretaceous to late Cenozoic. The full mountain belt consists of the pro-foreland southern Pyrenees and the retro-foreland northern Pyrenees, where the inverted lower Cretaceous rift system is mainly preserved. Due to low overall convergence and absence of oceanic subduction, this orogen preserves one of the best geological records of early orogenesis, the transition from early convergence to main collision and the transition from collision to post-convergence. During these transitional periods major changes in orogen behavior reflect evolving lithospheric processes and tectonic drivers. Contributions by the OROGEN project have shed new light on these critical periods, on the evolution of the orogen as a whole, and in particular on the early convergence stage. By integrating results of OROGEN with those of other recent collaborative projects in the Pyrenean domain (e.g., PYRAMID, PYROPE, RGF-Pyrénées), this paper offers a synthesis of current knowledge and debate on the evolution of this immature orogen as recorded in the synorogenic basins and fold and thrust belts of both the upper European and lower Iberian plates. Expanding insight on the role of salt tectonics at local to regional scales is summarised and discussed. Uncertainties involved in data compilation across a whole orogen using different datasets are discussed, for example for deriving shortening values and distribution

3D evolution of a retro-foreland basin : the Aquitaine Basin, France

Les bassins d'avant-pays se développent au front des orogènes par flexure de la lithosphère. L'héritage structural et thermique de celle-ci joue un rôle fondamental dans leur évolution et différentes sources peuvent contribuer à la subsidence du bassin. Cette thèse analyse les effets de l'héritage d'un épisode de rift sur un rétro-bassin d'avant-pays qui s'est développé alors que la lithosphère n'avait pas retrouvé son état d'équilibre. Le Bassin Aquitain est le rétro-bassin d'avant-pays pyrénéen qui s'est développé au Campanien-Miocène. L'orogenèse pyrénéenne fait suite à un épisode de rifting Aptien-Cénomanien durant lequel la croûte a été fortement amincie et le manteau sous-continental exhumé. Les effets de l'héritage crustal dus au rift sur l'évolution du bassin sont étudiés par une analyse des structures dans la croûte, du comportement flexural de la plaque européenne et de la distribution des sédiments synorogéniques. L'évolution de la subsidence dans le bassin est étudiée par analyse de subsidence 1D d'après des données de forages. Enfin, les mécanismes d'inversion de la marge européenne sont étudiés par restauration d'une coupe structurale à échelle crustale. Cette étude aide à définir le rôle de l'héritage d'un ancien système de rift sur la mise en place et l'évolution d'un bassin d'avant-pays ainsi que le rôle des différentes sources de subsidence et leurs variations spatio-temporelles. Cette étude démontre également les liens étroits entre l'histoire du rétro-bassin d'avant-pays et les mécanismes et phases d'inversion de la marge hyper-amincieForeland basins develop in front of orogens by flexure of the lithosphere. When they initiate over a crust that has been affected by a previous tectonic event, structural and thermal inheritance have a fundamental role in their evolution and different sources may contribute to basin subsidence. The present work analyzes the impact of inheritance from a rifting event on a foreland basin, which develops while thermal reequilibration has not been achieved at the time of loading. The Aquitaine Basin is the Pyrenean retro-foreland basin that developed from Campanian to Miocene. The Pyrenean orogenesis follows an Aptian-Cenomanian rifting during which the continental crust is thinned and sub-continental mantle exhumed. The orogenesis starts only 10 Myr after the end of rifting. The effects of crustal inheritance due to rifting on the evolution of the basin are studied by analyzing crustal structures, flexural behavior of the European plate, and foreland succession distribution. The subsidence evolution of the basin is studied by the 1D backstripping technique using borehole data. Finally, inversion mechanisms of the European margin are studied by cross-section construction and restoration at crustal scale. This study helps to define the role of rift inheritance on the initiation and the evolution of a retro-foreland basin, as well as the relative role of subsidence sources and their variations in space and time. The present work also shows the strong relationship between the retro-foreland basin's history and both mechanism and the history and mechanisms of inversion of a hyper-extended margi

Évolution 3D d'un rétro-bassin d'avant-pays : le Bassin aquitain, France

Foreland basins develop in front of orogens by flexure of the lithosphere. When they initiate over a crust that has been affected by a previous tectonic event, structural and thermal inheritance have a fundamental role in their evolution and different sources may contribute to basin subsidence. The present work analyzes the impact of inheritance from a rifting event on a foreland basin, which develops while thermal reequilibration has not been achieved at the time of loading. The Aquitaine Basin is the Pyrenean retro-foreland basin that developed from Campanian to Miocene. The Pyrenean orogenesis follows an Aptian-Cenomanian rifting during which the continental crust is thinned and sub-continental mantle exhumed. The orogenesis starts only 10 Myr after the end of rifting. The effects of crustal inheritance due to rifting on the evolution of the basin are studied by analyzing crustal structures, flexural behavior of the European plate, and foreland succession distribution. The subsidence evolution of the basin is studied by the 1D backstripping technique using borehole data. Finally, inversion mechanisms of the European margin are studied by cross-section construction and restoration at crustal scale. This study helps to define the role of rift inheritance on the initiation and the evolution of a retro-foreland basin, as well as the relative role of subsidence sources and their variations in space and time. The present work also shows the strong relationship between the retro-foreland basin's history and both mechanism and the history and mechanisms of inversion of a hyper-extended marginLes bassins d'avant-pays se développent au front des orogènes par flexure de la lithosphère. L'héritage structural et thermique de celle-ci joue un rôle fondamental dans leur évolution et différentes sources peuvent contribuer à la subsidence du bassin. Cette thèse analyse les effets de l'héritage d'un épisode de rift sur un rétro-bassin d'avant-pays qui s'est développé alors que la lithosphère n'avait pas retrouvé son état d'équilibre. Le Bassin Aquitain est le rétro-bassin d'avant-pays pyrénéen qui s'est développé au Campanien-Miocène. L'orogenèse pyrénéenne fait suite à un épisode de rifting Aptien-Cénomanien durant lequel la croûte a été fortement amincie et le manteau sous-continental exhumé. Les effets de l'héritage crustal dus au rift sur l'évolution du bassin sont étudiés par une analyse des structures dans la croûte, du comportement flexural de la plaque européenne et de la distribution des sédiments synorogéniques. L'évolution de la subsidence dans le bassin est étudiée par analyse de subsidence 1D d'après des données de forages. Enfin, les mécanismes d'inversion de la marge européenne sont étudiés par restauration d'une coupe structurale à échelle crustale. Cette étude aide à définir le rôle de l'héritage d'un ancien système de rift sur la mise en place et l'évolution d'un bassin d'avant-pays ainsi que le rôle des différentes sources de subsidence et leurs variations spatio-temporelles. Cette étude démontre également les liens étroits entre l'histoire du rétro-bassin d'avant-pays et les mécanismes et phases d'inversion de la marge hyper-aminci

Reconstruction cinématique de la limite de plaque diffuse Europe-Afrique pour étudier l'evolution de la Ceinture Orogénique Alpine en Méditerranée Occidentale

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Evolution of the Alpine orogenic belts in the Western Mediterranean region as resolved by the kinematics of the Europe-Africa diffuse plate boundary

The West European collisional Alpine belts are the result of the inversion, initiated in the middle Cretaceous, of the complex western Neotethys and the Atlantic continental rift domains and closure of remnants of Tethys between the North Africa and European cratons. While the kinematics of Africa relative to Europe is well understood, the kinematics of microplates such as Iberia and Adria within the diffuse collisional plate boundary is still a matter of debate. We review geological and stratigraphic constraints in the peri-Iberia fold-thrust belts and basins to define the deformation history and crustal segmentation of the West European realm. These data are then implemented with other constraints from recently published kinematic and paleogeographic reconstructions to propose a new regional tectonic and kinematic model for Western Europe from the late Permian to recent times. Our model suggests that the pre-collisional extension between Europe and Africa plates was distributed and oblique, hence building discontinuous rift segments between the southern Alpine Tethys and the Central Atlantic. They were characterised by variably extended crust and narrow oceanic domains segmented across transfer structures and micro-continental blocks. The main tectonic structures inherited from the late Variscan orogeny localized deformation associated with rifting and orogenic belts. We show that continental blocks, including the Ebro-Sardinia-Corsica block, have been key in accommodating strike-slip, extension, and contraction in both Iberia and Adria. The definition of a new Ebro-Sardinia-Corsica block allows refining the tectonic relationships between Iberia, Europe and Adria in the Alps. By the Paleogene, the convergence of Africa closed the spatially distributed oceanic domains, except for the Ionian basin. From this time onwards, collision spread over the different continental blocks from Africa to Europe. The area was eventually affected by the West European Rift, in the late Eocene, which may have controlled the opening of the West Mediterranean. The low convergence associated with the collisional evolution of Western Europe permits to resolve the control of the inherited crustal architecture on the distribution of strain in the collision zone, that is otherwise lost in more mature collisional domain such as the Himalaya

Space-time partitioning of the Mesozoic deformation alongthe Iberia/Eurasia diffuse plate boundary

National audienceSince the 1970s, the Mesozoic kinematic evolution of the Iberian plate has been largelydebated. In particular, no consensus exists on the timing, kinematics and partitioningof the deformation along the Iberia/Eurasia plate boundary during the Late Jurassic-Early Cretaceous. Most of the plate kinematics models suggest that this plate boundarymust have accommodated ~400 km of left-lateral displacement between the two platesin this time lapse. However, no field evidence exists for a narrow transform plateboundary that could have accommodated such displacement. In the last decade, severalauthors have tried to partition this deformation between two/three transtensionalcorridors centered in the Pyrenean realm, but still without resolving the discrepancybetween postulated and observed displacement. In this work, we propose a reappraisalof the Mesozoic Iberia/Eurasia plate boundary by reviewing the tectonic and kinematicevolution of the numerous rift basins located between the Iberian Chains System (to theS) and the Armorican Shelf/Northern Aquitaine System (to the N). This allows todefine the transition between the two plates as a~400 wide NW-SE trending diffuse plate boundary across which the deformation ispartitioned. Its polyphased evolution consists of four main steps: i) a Late Jurassicphase of left-lateral transtension localized at the northern and southern boundaries ofthe system, while the rest of the rift basins underwent orthogonal rifting; ii) aNeocomian phase of tectonic quiescence; iii) a Barremian-Aptian phase of diffuse leftlateraltranstensional rifting, while the North Pyrenean Rift System underwentorthogonal rifting; iv) an Albian- Cenomanian phase of transtension localized along theBasque-Cantabrian/North Pyrenean corridor, following the onset of oceanic spreadingin the Bay of Biscay margins, while the rest of the rift basins underwent post-rift stage.Finally, we discuss the role of structural inheritance and pre-rift salt in favoringdistributed rather than localized deformation at the plate boundary. This review allowsto make inferences on the timing of rotation of Iberia during the Mesozoic and tohighlight the contribution to the evolution of the plate boundary of some domainswithin the Cenozoic foreland basins of the Pyrenees which have been often disregarded

The Mesozoic Iberia-Eurasia diffuse plate boundary: A wide domain of distributed transtensional deformation progressively focusing along the North Pyrenean Zone

International audiencePlate kinematic reconstructions available for the Late Jurassic-Early Cretaceous eastward drift and counterclockwise rotation of the Iberian plate imply a major left-lateral motion of Iberia with respect to Eurasia. According to most authors, this displacement has been accommodated along the transform North Pyrenean Zone. However, no relevant field evidence exists for the proposed >400 km of horizontal displacement along the North Pyrenean Fault. Several Permian-Mesozoic basins are distributed around the Iberia/Eurasia plate boundary and have been more or less inverted during the Cenozoic Pyrenean Orogeny (i.e. Iberian Chain basins, North and South Pyrenean basins, Basque-Cantabrian Basin, Parentis Basin, Bay of Biscay/Asturian margins). All of these basins experienced a complex kinematic history and shared the same tectono-stratigraphic evolution, with two successive rifting stages: (i) Permian-Triassic rifting following the dismantling of the Variscan belt and recording the early breakup of Pangea and (ii) Late Jurassic-Early Cretaceous rifting developing after a Jurassic post-rift thermal cooling stage. Depending on the different techniques of investigation and on the interpretation of controversial datasets, authors proposed either opening by orthogonal rifting or by transtensional/pull-apart tectonics for these basins.In this work, we propose a reappraisal of the processes responsible for the Mesozoic Iberia/Eurasia plate boundary compartmentalization by reviewing the tectono-sedimentary history and the kinematic evolution of the sedimentary basins involved in this domain. We shed light on the fact that the Cretaceous left-lateral movement within the plate boundary was not accommodated by localized deformation along the single North Pyrenean Fault wrench structure, but rather by a distributed zone of deformation in which the transtensional regime was recorded by the sedimentary basins therein. We also suggest that other Permian-Mesozoic depocenters located below the Cenozoic foreland basins of the Pyrenean belt (i.e. the Ebro and Aquitaine basins) may have been active segments of this rift system. We then propose that the real extent of the Mesozoic plate boundary is roughly defined by two NW-SE trending lineaments corresponding to the southwestern margin of the Iberian Chain, on the Iberian side, and to the southern Armorican margin and the southwestern border of the French Central Massif, on the Eurasian side. The complex pre-Cretaceous tectono-sedimentary history of this region determined its peculiar pre-rift structure. Such structural inheritance may have favored a distributed rather than a localized mode of deformation at the Iberia/Eurasia diffuse plate boundary during the Late Jurassic-Early Cretaceous, whilst mechanisms related to the eastward propagation of the Bay of Biscay system might have been responsible for the final localization of the plate boundary along the Basque-Cantabrian/North Pyrenean corridor

Space-time partitioning of the Mesozoic deformation along the Iberia/Eurasia diffuse plate boundary

International audienc

Space-time partitioning of the Mesozoic deformation alongthe Iberia/Eurasia diffuse plate boundary

National audienceSince the 1970s, the Mesozoic kinematic evolution of the Iberian plate has been largelydebated. In particular, no consensus exists on the timing, kinematics and partitioningof the deformation along the Iberia/Eurasia plate boundary during the Late Jurassic-Early Cretaceous. Most of the plate kinematics models suggest that this plate boundarymust have accommodated ~400 km of left-lateral displacement between the two platesin this time lapse. However, no field evidence exists for a narrow transform plateboundary that could have accommodated such displacement. In the last decade, severalauthors have tried to partition this deformation between two/three transtensionalcorridors centered in the Pyrenean realm, but still without resolving the discrepancybetween postulated and observed displacement. In this work, we propose a reappraisalof the Mesozoic Iberia/Eurasia plate boundary by reviewing the tectonic and kinematicevolution of the numerous rift basins located between the Iberian Chains System (to theS) and the Armorican Shelf/Northern Aquitaine System (to the N). This allows todefine the transition between the two plates as a~400 wide NW-SE trending diffuse plate boundary across which the deformation ispartitioned. Its polyphased evolution consists of four main steps: i) a Late Jurassicphase of left-lateral transtension localized at the northern and southern boundaries ofthe system, while the rest of the rift basins underwent orthogonal rifting; ii) aNeocomian phase of tectonic quiescence; iii) a Barremian-Aptian phase of diffuse leftlateraltranstensional rifting, while the North Pyrenean Rift System underwentorthogonal rifting; iv) an Albian- Cenomanian phase of transtension localized along theBasque-Cantabrian/North Pyrenean corridor, following the onset of oceanic spreadingin the Bay of Biscay margins, while the rest of the rift basins underwent post-rift stage.Finally, we discuss the role of structural inheritance and pre-rift salt in favoringdistributed rather than localized deformation at the plate boundary. This review allowsto make inferences on the timing of rotation of Iberia during the Mesozoic and tohighlight the contribution to the evolution of the plate boundary of some domainswithin the Cenozoic foreland basins of the Pyrenees which have been often disregarded

EVOLUTION OF THE PYRENEAN AQUITAINE FORELAND BASIN (SW FRANCE)

International audienceThe Aquitaine basin is the retro-foreland basin associated with the Pyrenean orogen. It developed fromCampanian to Mid-Miocene by flexure of the upper (European) plate. The foreland basin forms a synorogenicsedimentary wedge up to 5.5 km thick in the south, thinning rapidly north. The synorogenic series migratesnorthward. The paleo-geographic history of the Aquitaine Basin shows an evolution from deep marine tocontinental facies. The continental to marine transition also migrates to the west. We study the spatio-temporalevolution of tectonic subsidence in the Aquitaine foreland basin, in order to understand the role of differentsources of subsidence at each stage of basin evolution. Our analyses show that the tectonic subsidence in theAquitaine Basin is a combination of flexural subsidence, caused by the Pyrenean orogen and dense mantlebodies within the upper crust, and post-rift thermal subsidence inherited from Early Cretaceous rifting. Thepost-rift thermal subsidence increases westward, reaching its maximum above inherited rift-basins (Parentisand Arzacq rift-basins). In the central Aquitaine Basin, two foreland successions are recognized, correspondingto distinct stages in the tectonic evolution of the Pyrenean orogenic system. The first succession (Campano-Maastrichtian) was deposited during the early inversion of the rifted domain. Early loading on the southernpart of the European plate was synchronous with post-rift thermal subsidence during this stage. The secondforeland succession (Eocene to Mid-Miocene) was deposited during main continental collision of the Pyrenees.These two foreland successions are separated by a Paleocene quiet phase. We show that the inherited thermalsubsidence strongly influenced facies distribution and the evolution of the flexural Aquitaine foreland basin