Extending Continental Lithosphere With Lateral Strength Variations: Effects on Deformation Localization and Margin Geometries

We investigate the development of margin geometries during extension of a continental lithosphere containing lateral strength variations. These strength variations may originate from the amalgamation of continents with different mechanical properties as was probably the case when Pangea was assembled. Our aim is to infer if localization of deformation is controlled by the boundary between two lithospheres with different mechanical properties (e.g., “weak” and “strong”) or not. We ran a series of lithosphere-scale physical analog models in which we vary the strength contrast across equally sized lithospheric domains. The models show that deformation always localizes in the relatively weaker compartment, not at the contact between the two domains because the contact is unfavorably oriented for the applied stress and does not behave as a weak, inherited discontinuity. Wide-rifts develop under coupled conditions when the weak lithosphere consists of a brittle crust, ductile crust and ductile mantle. When a brittle upper mantle layer is included in the weak segment, the rift system develops in two phases. First, a wide rift forms until the mechanically strong upper mantle develops a necking instability after which the weak lower crust and weak upper mantle become a coupled, narrow rift system. The margin geometries that result from this two-phase evolution show asymmetry in terms of crustal thickness and basin distribution. This depends heavily on the locus of failure of the strong part of the upper mantle. The models can explain asymmetric conjugate margin geometries without using weak zones to guide deformation localization

The interaction between Aegean back-arc extension and Anatolia escape since Middle Miocene

International audienceThe Aegean domain is a key area for understanding the processes of back-arc extension. Observed deformation pattern and present day kinematics result from the interaction between the southward retreat of the Hellenic trench and the westward escape of Anatolia. Lithosphere-scale analogue models were employed to display that the overall pattern of Aegean extension requires not only the combination of trench retreat and Anatolia escape since middle Miocene but also the presence of an inherited lithosphere-scale mechanical discontinuity: the Vardar Suture Zone (VSZ). The reactivation in dextral shear of the eastern branch of the VSZ accommodates both the trench retreat (NS stretching) and the westward escape of Anatolia (EW shortening) in the Cyclades area since middle Miocene. Additionally, our model shows that the North Anatolian Fault (NAF) is a late structure in the evolution of the Aegean, initiated around 10 Ma after the onset of Anatolia escape. The displacement field at the surface of the model allows the identification of sub-domains, which result from strain partitioning instead of being "rigid microplates", directly comparable to the present-day displacement field (GPS) of the Aegean and western Anatolia. Our model provides a simple but powerful way to look at the dynamics of Aegean extension in two main stages. From middle Eocene to middle Miocene, extension was only driven by the southward retreat of the Hellenic trench at a rate lower than 1 cm*y− 1. Since middle Miocene, the combination of slab rollback with Anatolia westward escape resulted in a southwest direction of trench retreat, with an accelerating rate of up to 3 cm*y− 1

The two-stage aegean extension, from localized to distributed, a result of slab rollback acceleration

International audienceBack-arc extension in the Aegean, which was driven by slab rollback since 45 Ma, is described here for the first time in two stages. From Middle Eocene to Middle Miocene, deformation was localized leading to i) the exhumation of high-pressure metamorphic rocks to crustal depths, ii) the exhumation of high-temperature metamorphic rocks in core complexes and iii) the deposition of sedimentary basins. Since Middle Miocene, extension distributed over the whole Aegean domain controlled the deposition of onshore and offshore Neogene sedimentary basins. We reconstructed this two-stage evolution in 3D and four steps at Aegean scale by using available ages of metamorphic and sedimentary processes, geometry and kinematics of ductile deformation, paleomagnetic data and available tomographic models. The restoration model shows that the rate of trench retreat was around 0.6 cm/y during the first 30 My and then accelerated up to 3.2 cm/y during the last 15 My. The sharp transition observed in the mode of extension, localized versus distributed, in Middle Miocene correlates with the acceleration of trench retreat and is likely a consequence of the Hellenic slab tearing documented by mantle tomography. The development of large dextral NE-SW strike-slip faults, since Middle Miocene, is illustrated by the 450 Km-long fault zone, offshore from Myrthes to Ikaria and onshore from Izmir to Balikeshir, in western Anatolia. Therefore, the interaction between the Hellenic trench retreat and the westward displacement of Anatolia started in Middle Miocene, almost 10 Ma before the propagation of the North Anatolian Fault in the North Aegean

On-offshore Lithospheric folding in the Iberian Plate

Los principales rasgos de la topografía de Iberia, tanto onshore, como en el offshore Atlántico, son el resultado del desarrollo de pliegues litosféricos desacoplados de los de la Corteza Superior bajo un contexto de acercamiento N-S entre Iberia y Eurasia durante el Oligoceno – Mioceno Inferior. El acoplamiento mecánico entre Iberia y África, produjo una deformación muy distribuida hasta el Anti-Atlas en Marruecos. El emplazamiento del Bloque de Alborán desacopló Iberia de África de E a O, con lo que sólo en la zona más Occidental de la Península Ibérica, y en el offshore Atlántico, continúa aún activo este proceso.The main topographic features of Iberia, onshore and in the Atlantic offshore, are the result of the development of Lithospheric folding and decoupled Upper Crustal folds under a N-S approach between Iberia and Eurasia during the Oligocene-Lower Miocene. The mechanical coupling between Iberia and Africa, produced a very distributed deformation up to the Anti-atlas in Morocco. The emplacement of the Alboran Block decoupled Africa from Iberia from E to W, with what only in the westernmost zone of the Iberian Peninsula, and in the Atlantic offshore, this process still continues nowadays.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Educación y Ciencia (MEC)Consolider Ingenio 2006pu

Integrated analysis of topography and gravity anomalies in analogue modelling: a model of relief evolution in the Iberian Peninsula

El análisis integrado de la topografía y las anomalías gravimétricas en la Península Ibérica invoca a la presencia de grandes pliegues que afectan a toda la litosfera como precursores de los relieves E-O a NE-SO que se distribuyen por el Macizo Varisco, así como a un mecanismo de engrosamiento cortical nucleado a partir de fallas Tardi-Variscas, como origen del relieve del este peninsular (Cadena Ibérica-Costero Catalana) con patrones dominantes E-O, NE-SO y NO-SE. El modo de deformación, así como el estilo, dependen tanto de las propiedades reológicas iniciales de una litosfera a otra (litosfera resistente Varisca hacia el oeste peninsular/litosfera débil y caliente resultado de la extensión Mesozoica hacia el este) como a los accidentes tectónicos pre-existentes. Presentamos una nueva metodología aplicada a la modelación análoga, basada en el estudio del espectro de las anomalías gravimétricas y la topografía que nos han permitido inferir los procesos responsables de la asimetría en el patrón del relieve intra-placa de la Península Ibérica. A su vez, nuestros resultados arrojan luz sobre los mecanismos generadores del relieve en zonas de intra-placa donde la escasez o falta de resolución de los perfiles sísmicos y geomagnéticos impide la interpretación de la parte más profunda de la litosfera como Asia Central o los Atlas del norte de ÁfricaThe integrated analysis of topography and gravity anomalies carried out in the Iberian Peninsula invokes to the presence of large-scale folds affecting the entire lithosphere. Such folds are the precursors of E-W to NE-SO reliefs distributed along the Variscan Massif, meanwhile a mechanism of crustal thickening nucleated along Late-Variscan faults can influence the topographic pattern in the eastern part of Iberia (Iberian Range-Costero Catalan Ranges) characterised by E-W, NE-SW and NWSE trends. The mechanism of deformation as well as the style depends on the initial rheological properties from one lithosphere to another (strong and cold Variscan lithosphere to the west and a relative weak and hot lithosphere affected by the Mesozoic extension to the east) and influenced by pre-existent faults. We present a new approach based on the spectral analyses of topography and gravity over the analogue modelling results that can help to infer the responsible mechanisms for the observed intra-plate relief asymmetry in Iberia. Our results enhance the study of other areas within plate interiors like Central Asia or the Atlas in northern Africa, where the lack of data or resolution from deep seismic profiles or geomagnetics may hamper the interpretation of the lithosphere in depthDepto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEEspaña. Plan Nacional de Investigación Científica y Desarrollo Tecnológicopu

Integrated analysis of topography and gravity anomalies in analogue modelling: a model of relief evolution in the Iberian Peninsula

El análisis integrado de la topografía y las anomalías gravimétricas en la Península Ibérica invoca a la presencia de grandes pliegues que afectan a toda la litosfera como precursores de los relieves E-O a NE-SO que se distribuyen por el Macizo Varisco, así como a un mecanismo de engrosamiento cortical nucleado a partir de fallas Tardi-Variscas, como origen del relieve del este peninsular (Cadena Ibérica-Costero Catalana), con patrones dominantes E-O, NE-SO y NO-SE. El modo de deformación, así como el estilo, dependen tanto de las propiedades reológicas iniciales de una litosfera a otra (litosfera resistente Varisca hacia el oeste peninsular/litosfera débil y caliente resultado de la extensión Mesozoica hacia el este) como a los accidentes tectónicos pre-existentes. Presentamos una nueva metodología aplicada a la modelación análoga, basada en el estudio del espectro de las anomalías gravimétricas y la topografía que nos han permitido inferir los procesos responsables de la asimetría en el patrón del relieve intra-placa de la Península Ibérica. A su vez, nuestros resultados arrojan luz sobre los mecanismos generadores del relieve en zonas de intra-placa donde la escasez o falta de resolución de los perfiles sísmicos y geomagnéticos impide la interpretación de la parte más profunda de la litosfera como Asia Central o los Atlas del norte de África.The integrated analysis of topography and gravity anomalies carried out in the Iberian Peninsula invokes to the presence of large-scale folds affecting the entire lithosphere. Such folds are the precursors of E-W to NE-SO reliefs distributed along the Variscan Massif, meanwhile a mechanism of crustal thickening nucleated along Late-Variscan faults can influence the topographic pattern in the eastern part of Iberia (Iberian Range-Costero Catalan Ranges) characterised by E-W, NE-SW and NW-SE trends. The mechanism of deformation as well as the style depends on the initial rheological properties from one lithosphere to another (strong and cold Variscan lithosphere to the west and a relative weak and hot lithosphere affected by the Mesozoic extension to the east) and influenced by pre-existent faults. We present a new approach based on the spectral analyses of topography and gravity over the analogue modelling results that can help to infer the responsible mechanisms for the observed intra-plate relief asymmetry in Iberia. Our results enhance the study of other areas within plate interiors like Central Asia or the Atlas in northern Africa, where the lack of data or resolution from deep seismic profiles or geomagnetics may hamper the interpretation of the lithosphere in depth.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu