<p>&#160; &#160; The Valencia Trough is commonly included as part of the set of western Mediterranean Cenozoic extensional basins that formed in relation with the Tethyan oceanic slab rollback during the latest Oligocene to early Miocene. It lies in a complex tectonic setting between the Gulf of Lions to the North-West, the Catalan Coastal Range and the Iberian chain to the West, the Balearic promontory to the East and the Betic orogenic system to the South. This rifting period is coeval with or directly followed by the development of the external Betics fold and thrust belts at the southern tip of the Valencia Trough. Recent investigations suggest that the Valencia Trough is segmented into two main domains exhibiting different geological and geophysical characteristics between its northeastern and southwestern parts. The presence of numerous Cenozoic normal faults and the well-studied subsidence pattern evolution of the NE part of the Valencia Trough suggest that it mainly formed coevally with the rifting of Gulf of Lion. However, if a significant post-Oligocene subsidence is also evidenced in its SW part; fewer Cenozoic rift structures are observed suggesting that the subsidence pattern likely results from the interference of different processes.</p><p>&#160; &#160; In this presentation, we quantify the post-Oligocene subsidence history of the SW part of the Valencia Trough with the aim of evaluating the potential mechanisms explaining this apparent subsidence discrepancy. We analyzed the spatial and temporal distribution of the post-Oligocene subsidence using the interpretation of a dense grid of high-quality multi-channel seismic profiles, also integrating drill-hole results and velocity information from expanding spread profiles (ESP). We used the mapping of the main unconformities, especially the so-called Oligocene unconformity, to perform a 3D flexural backstripping, which permits the prediction of the post-Oligocene water-loaded subsidence. Our results confirm that the post-Oligocene subsidence of the SW part of the Valencia Trough cannot be explained by the rifting of the Gulf of Lions. Previous works already showed that the extreme crustal thinning observed to the SW is related to a previous Mesozoic rift event. Here, we further highlight that if few Cenozoic extensional structures are observed, they can be interpreted as gravitational features rooting at the regionally identified Upper Triassic evaporite level. Backstripping results combined with the mapping of the first sediments deposited on top of the Oligocene unconformity show that they are largely controlled by the shape of Betic front with a possible additional effect of preserved Mesozoic structures. At larger scale, we compare the mechanisms accounting for the origin and subsidence at the SW part of the Valencia Trough with those responsible for the subsidence of its NE part and the Gulf of Lions.</p>
Rifted margins are often classified as magma-poor or magma-rich based on a magmatic budget interpretation from seismic reflection data. The southern segment of the East Indian rifted margin is often regarded as a type-example of a magma-poor margin displaying exhumed mantle. However, in its southern segment, 9 km thick transitional crust, previously interpreted as magmatic crust, separates the exhumed mantle from thin oceanic crust. Such thick transitional crust is atypical for a magma-poor margin, so we investigate its likely formation and potential implications for the evolution of magma-poor margins. Using an integrated set of geophysical techniques alongside seismic reflection data, we test the existence of exhumed mantle and the composition of the transitional crust. These geophysical techniques consist of gravity inversion, residual depth anomaly analysis, flexural subsidence analysis and joint inversion of gravity and seismic data. We apply these methods to high-quality seismic reflection data (ION line INE1-1000) on the southern segment of the East Indian rifted margin and test a series of geological scenarios for the margin structure using our integrated quantitative analysis. Of these, our quantitative analysis, seismic observations and the regional plate kinematic history support a structure consisting of thinned continental crust inboard of exhumed, serpentinized mantle followed by thick (∼9 km) magmatic crust transitioning into thin oceanic crust (∼5 km). The juxtaposition of exhumed mantle and thick magmatic crust is explained by the occurrence of a jump in seafloor spreading during the Early Cretaceous formation of the south-east Indian Ocean. The final rifted margin structure contains characteristics of both magma-poor and magma-rich rifted margins resulting from two distinct rift events with different magmatic budgets. The investigation of the East Indian rifted margin structure and evolution shows the importance of incorporating the plate kinematic history and quantitative validation of seismic interpretation into the analysis. Classifying the East Indian margin as a typical magma-poor rifted margin is misleading causing us to question the use of end-member terminology to describe rifted margins.
Abstract We investigate the thermal and structural evolution of asymmetric rifted margin using numerical modeling and geological observations derived from the Western Pyrenees. Our numerical model provides a self‐consistent physical evolution of the top basement heat flow during asymmetric rifting. The model shows a pronounced thermal asymmetry that is caused by migration of the rift center toward the upper plate. The same process creates a diachronism for the record of maximum heat flow and maximum temperatures ( T max ) in basal rift sequences. The Mauléon‐Arzacq basin (W‐Pyrenees) corresponds to a former mid‐Cretaceous asymmetric hyperextended rift basin. New vitrinite reflectance data in addition to existing data sets from this basin reveal an asymmetry in the distribution of peak heat ( T max ) with respect to the rift shoulders, where highest values are located at the former upper‐ to lower‐plate transition. This data set from the Arzacq‐Mauléon field study confirms for the first time the thermal asymmetry predicted by numerical models. Numerical modeling results also suggest that complexities in synrift thermal architecture could arise when hanging‐wall‐derived extensional allochthons and related T max become part of the lower plate and are transported away from the upper‐ to lower‐plate transition. This study emphasizes the limitations of the common approach to integrate punctual thermal data from pre‐rift to synrift sedimentary sequences in order to describe the rift‐related thermal evolution and paleothermal gradients at the scale of a rift basin or a rifted margin.
Crustal geometries imaged at rifted margins show contrasted first-order morphologies (wide and narrow, symmetric or asymmetric conjugates). This contribution aims to review the mechanisms of continental lithospheric thinning and types of extensional structures that control the formation of rifted margins. We illustrate, using a two-layer numerical model (one for the crust and one for the mantle), how different modes of lithospheric thinning shape the end-member crustal geometries of rifted margins depending on the initial thermal conditions and extension rates. As already known, the activation of narrow or wide modes of lithospheric thinning depends on the rheological behaviour of the lower crust and its efficiency as a decoupling layer. Morphologies generated by narrow lithospheric thinning modes compare well with Atlantic-type rifted margins (e.g., Iberia–Newfoundland) while wide lithospheric thinning modes better apply to marginal seas characterized by higher initial geothermal gradients (e.g., South China Sea). Finally, we also emphasize that continental lithosphere thinning is depth-dependent, part of which is transient and cannot easily be measured in natural systems. Supplementary Materials: Supplementary material for this article is supplied as a separate file: crgeos-257-suppl.zip L'architecture crustale des marges passives imagée par les méthodes géophysiques est contrastée montrant des morphologies tantôt larges ou étroites, les profils conjugués pouvant être symétriques ou asymétriques. Cette contribution présente les mécanismes d'amincissement de la lithosphère continentale et les différents types de structures extensives qui contrôlent la formation des marges passives. L'utilisation d'un modèle à deux couches (une pour la croûte et une pour le manteau), permet d'illustrer comment les différents modes d'amincissement de la lithosphère façonnent l'architecture premier ordre des marges passives pour différents taux d'extension et conditions thermiques initiales. Comme précédemment démontré, l'activation d'un mode d'amincissement de la lithosphère étroit/localisé ou large/distribué dépend du comportement rhéologique de la croûte inférieure et de son efficacité en tant que niveau de découplage. Les morphologies générées par un amincissement lithosphérique étroit et localisé sont comparables à celles observées dans les marges passives de type atlantique (par exemple, Ibérie–Terre-Neuve). Le modèle d'amincissement large et distribué s'applique mieux aux mers marginales caractérisées par des gradients géothermiques initiaux plus élevés (par exemple, la mer de Chine méridionale). Enfin, nous soulignons également que l'amincissement de la lithosphère continentale dépend de la profondeur et qu'il est en partie transitoire, une des raisons pour lesquelles, il n'est pas facile de le mesurer dans les systèmes naturels. Compléments : Des compléments sont fournis pour cet article dans le fichier séparé : crgeos-257-suppl.zip
