| 1. |
- Cadenas, Patricia, et al.
(författare)
-
The role of extensional detachment systems in thinning the crust and exhuming granulites : analogies between the offshore Le Danois High and the onshore Labourd Massif in the Biscay/Pyrenean rifts
- 2021
-
Ingår i: Bulletin de la Société Géologique de France. - : EDP Sciences. - 0037-9409 .- 1777-5817. ; 192
-
Tidskriftsartikel (refereegranskat)abstract
- Large uncertainties remain about the architecture, timing and role of the structures responsible for high degrees of crustal thinning and the exhumation of mid-crustal granulites in the Pyrenean and Biscay rift systems. Both, the Le Danois High in the North Iberian margin and the Labourd Massif in the Western Pyrenees preserve evidence of extensional detachment faults and include exhumed granulites, which are locally reworked in syn-rift sediments. In this study, we compare the crustal structure and its link to the overlying sediments at the two sites based on the interpretation of high quality 2D seismic reflection profiles offshore and field observations and published geological cross-sections onshore. New reported seismic and field observations support that extensional detachment systems delineate the top basement in the Le Danois High and the Labourd Massif, advocating for a similar tectonic evolution. We propose that the Le Danois and North Mauleon extensional detachment systems were responsible for high degrees of crustal thinning and the exhumation of the pre-rift brittle-ductile transition and associated mid-crustal granulites during Aptian to Cenomanian extension, leading to the formation of the Le Danois and Labourd crustal tapers. Subsequently tilted and uplifted during the Alpine convergence, the two taper blocks lay at present in the hanging-wall of major Alpine thrusts. Their position at overlapping, en-echelon hyperextended rift segments at the end of rifting, and the occurrence of shortcutting structures at depth linking neighbouring rift segments can explain the preservation of the rift-related detachment systems. This study proposes for the first time analogies between the offshore Le Danois High and the onshore Labourd Massif and demonstrates the importance of extensional detachment systems in thinning the crust and exhuming mid-crustal granulites at the seafloor in the Biscay and Pyrenean rift systems during Aptian to Cenomanian extension.
|
|
| 2. |
- Engström, Anna, 1975-
(författare)
-
Deformation and fluid-flow in magma-poor margins : A study of the Tasna Ocean-Continent transition, SE Switzerland
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this study, interaction between fluids and deformation during the final stages of magma-poor rifting was investigated. The Tasna Ocean-Continent transition, located in the Swiss Alps, was studied and a large data set was obtained from profiles oriented perpendicular to two detachment faults. One of these juxtaposed serpentinized mantle against continental crust and the other exhumed both mantle and continental crust to the seafloor. Deformation associated with detachment faulting showed many common features but also some phenomena which were unique to each fault, confirming their sequential activity and differing roles in the exhumation process. Oxygen isotopes indicated the presence of both pervasive and channeled fluid phases, either accompanying or post-dating serpentinization. Deformation in the fault zone occurred in previously serpentinized mantle indicating that serpentinization pre-dated final exhumation. Most strain localization and displacement occurred in fault cores which are narrow zones beneath the detachments. These are underlain by wide zones characterized by more distributed strain. Transitional fabrics as well as reactivated and/or overprinted deformation structures indicated that the final phase of rifting is complex. Fault cores acted as fluid conduits or barriers. Thus, the most deformed zones may become the least permeable. Hence the coupling between deformation and fluid flow is complex in a study area subjected to several phases of deformation and fluid flow. Finally the importance of serpentinization in the evolution of magma-poor rifting was investigated. It was found that serpentinization is the consequence rather than the reason for strain localization at magma-poor margins. However, serpentinization may be an important process which can accelerate exhumation rates in the very latest stages of magma-poor rifting. The pre-existing deformation history of the crust may also be of importance for the development and location of margins.
|
|
| 3. |
- Frasca, Gianluca, et al.
(författare)
-
A kinematic reconstruction of Iberia using intracontinental strike-slip corridors
- 2021
-
Ingår i: Terra Nova. - : John Wiley & Sons. - 0954-4879 .- 1365-3121. ; 33:6, s. 573-581
-
Tidskriftsartikel (refereegranskat)abstract
- Despite considerable progress in restoring rifted margins, none of the current kinematic models can restore the Mesozoic motion of the Iberian block in full agreement with the circum-Iberian geology. This conflict requires a revision of the kinematic description at the onset of divergence. The circum-Iberian region has a unique geological dataset that allows calibration and testing of kinematic reconstructions and therefore it is an ideal candidate for testing intracontinental restoration approaches. Here we define intracontinental deforming regions, referred to as strike-slip corridors, based on alignments of Mesozoic rift basins and/or transfer zones bordering rigid continental blocks. We use these strike-slip corridors and data from the southern N-Atlantic and Tethys to define the motion path of the Flemish Cap, Ebro and Iberia continental blocks. The resulting Mesozoic kinematic model for the Iberian block is compatible with recently published data and interpretations describing the Mesozoic circum-Iberian geology. Large-scale intracontinental strike-slip corridors may offer a valid boundary condition for reconstructing continental block motion at the onset of divergence in intracontinental settings.
|
|
| 4. |
- Lescoutre, Rodolphe, et al.
(författare)
-
Role of rift-inheritance and segmentation for orogenic evolution : example from the Pyrenean-Cantabrian system
- 2020
-
Ingår i: Bulletin de la Société Géologique de France. - : EDP SCIENCES S A. - 0037-9409 .- 1777-5817. ; 191
-
Tidskriftsartikel (refereegranskat)abstract
- The Basque-Cantabrian junction corresponds to an inverted rift accommodation zone at the limit between the former hyperextended Pyrenean and Cantabrian rift segments. The recognition of an inherited rift segment boundary allows to investigate the reactivation associated with large-scale rift segmentation in an orogenic system. We use criteria from published field observations and seismic data to propose a new map of rift domains for the Basque-Cantabrian junction. We also provide balanced cross-sections that allow to define the along-strike architecture associated with segmentation during rifting and subsequent Alpine reactivation. Based on these results, this study aims to characterize and identify reactivated and newly formed structures during inversion of two rift segments and its intermitted segment boundary. It also aims to describe the timing of thin-skinned and thick-skinned deformation associated with the inversion of segmented rift systems. During convergence, two phases have been recognized within the rift segment (eastern Mauleon basin). The Late Cretaceous to Paleocene underthrusting/subduction phase was mostly governed by thin-skinned deformation that reactivated the former hyperextended domains and the supra-salt sedimentary cover. The Eocene to Miocene collisional phase, controlled by thick-skinned deformation that took place once necking domains collided and formed an orogenic wedge. At the rift segment boundary, the underthrusting/subduction phase was already controlled by thick-skinned deformation due to the formation of shortcutting thrust faults at the termination of overlapping V-shaped rift segments. This led to the formation of a proto-wedge composed of the Basque massifs. We suggest that this proto-wedge is responsible for the preservation of pre-Alpine structures in the Basque massifs and for the emplacement of subcontinental mantle rocks at a crustal level beneath the western Mauleon basin. These results argue for a first order cylindrical orogenic architecture from the Central Pyrenean segment to the Cantabrian segment (up to the Santander transfer zone) despite rift segmentation. They also highlight the control of 3D rift-inheritance for the initial phase of orogenic evolution and for the local architecture of mountain belts. La jonction pyreneo-cantabrique correspond a une zone d'accommodation entre les segments de rifts hyper-etires cantabrique et pyreneen, qui ont ete par la suite inverses lors de l'orogenese alpine. La reconnaissance d'une telle zone de segmentation permet d'etudier les consequences d'un heritage de rift en 3dimensions sur l'evolution orogenique. A partir de nos precedents resultats ainsi que de la compilation de donnees de terrain et de sismique, nous proposons une nouvelle carte des domaines de rift dans la zone etudiee. L'elaboration de coupes restaurees permet de definir et comparer l'architecture actuelle et syn-rift entre la zone d'accommodation et les segments de rift (c.a.d. a distance de la zone de segmentation). A partir de ces resultats, cette etude vise a identifier et caracteriser les structures reactivees et neo-formees a travers la zone d'etude. Elle entreprend egalement de decrire l'evolution de la deformation << thin-skinned >> et << thick-skinned >> au cours de la convergence dans ce type de systeme tres segmente. Lors de la convergence, deux phases de deformation peuvent etre distinguees dans les segments de rift (bassin Est Mauleon). Une phase de sous-charriage tardi-Cretace a Paleocene, principalement controlee par la deformation << thin-skinned >> et qui reactive les domaines de rift hyper-etires ainsi que la couverture Mesozoique decollee sur les evaporites du Trias Superieur. Une phase de collision Eocene a Miocene, qui s'initie lorsque les domaines d'etranglement des marges conjuguees se rencontrent et qui mene a la formation d'un prisme orogenique (<< thick-skin >>). Dans la zone d'accommodation, la phase de sous-charriage semble deja controlee par la deformation << thick-skinned >> par la formation de structures crustales neo-formees a vergences opposees a la terminaison des bassins. Ces dernieres transferent la deformation entre les deux segments de rifts et forment un proto-prisme orogenique compose des massifs basques. Nous suggerons que ce proto-prisme orogenique est responsable de la preservation des structures pre-alpines dans les massifs basques ainsi que de l'emplacement a faible profondeur du manteau sous-continental sous le bassin Ouest Mauleon. Cette etude montre que l'architecture orogenique apparait au premier ordre cylindrique des Pyrenees Centrales au segment cantabrique (jusqu'a la zone de Santander), malgre la segmentation du systeme de rift sur lequel la deformation s'initie. Elle souligne enfin le role de l'architecture heritee en 3dimensions lors des phases precoces de l'evolution orogenique ainsi que pour l'architecture locale de l'orogene.
|
|
| 5. |
- Manatschal, Gianreto, et al.
(författare)
-
The role of inheritance in forming rifts and rifted margins and building collisional orogens : a Biscay-Pyrenean perspective
- 2021
-
Ingår i: Bulletin de la Société Géologique de France. - : EDP Sciences. - 0037-9409 .- 1777-5817. ; 192
-
Tidskriftsartikel (refereegranskat)abstract
- A long-standing challenge in tectonics is to evaluate the role of inheritance and define the initial conditions of a geodynamic system, which are prerequisites to understand and model its evolution with some accuracy. Here we revisit the concept of "inheritance" by distinguishing "interface shape inheritance", which includes the transient thermal state and gravitational potential energy, and "persisting inheritance", which encompasses long-lasting structural and compositional inheritance. This new approach allows us to investigate, at each stage of a Wilson Cycle, the interplay between inheritance (innate/"genetic code") and the physical processes at play (extension/compression, magmatism etc.). The aim of this paper is to provide a conceptual framework that integrates the role of inheritance in the study of rifts, rifted margins and collisional orogens based on the work done in the OROGEN project, which focuses on the Biscay-Pyrenean system. The Biscay-Pyrenean rift system resulted from a multistage rift evolution that developed over a complex lithosphere pre-structured by the Variscan orogenic cycle. There is a general agreement that the Pyrenean-Cantabrian orogen resulted from the reactivation of an increasingly mature rift system along-strike, ranging from mature rifted margins in the west to an immature and segmented hyperextended rift in the east. However, different models have been proposed to explain the preceding rifting and its influence on the subsequent reactivation. Results from the OROGEN project highlight the sequential reactivation of rift-inherited decoupling horizons and identify the specific role of exhumed mantle, hyperextended and necking domains during compressional reactivation. They also highlight the contrasting fate of rift segment centres versus segment boundaries during convergence, explaining the non-cylindricity of internal parts of collisional orogens. Results from the OROGEN project also suggest that the role of inheritance is more important during the initial stages of collision, which may explain the higher complexity of internal parts of orogenic systems with respect to their external parts. In contrast, when the system involved in the orogeny is more mature, the orogenic evolution is mostly controlled by first-order physical processes as described in the Coulomb Wedge theory, for instance. This may account for the simpler and more continuous architecture of external parts of collisional orogens and may also explain why most numerical models can reproduce mature orogenic architectures with a better accuracy compared to those of initial collisional stages. The new concepts developed from the OROGEN research are now ready to be tested at other orogenic systems that result from the reactivation of rifted margins, such as the Alps, the Colombian cordilleras and the Caribbean, Taiwan, Oman, Zagros or Timor.
|
|
| 6. |
- Merle, Renaud, 1976-, et al.
(författare)
-
Origin of widespread Cretaceous alkaline magmatism in the Central Atlantic : A single melting anomaly?
- 2019
-
Ingår i: Lithos. - 0024-4937 .- 1872-6143. ; 342-343, s. 480-498
-
Tidskriftsartikel (refereegranskat)abstract
- The age and origin of the Late Cretaceous magmatism on the North American and Iberian-African margins and the adjacent northern Central and Southern North Atlantic ocean are not well constrained due to the lack of appropriate data. To solve this issue, we used the 40Ar/39Ar geochronology and Sr-Nd-Pb isotopes geochemistry of basalts from the New England Seamounts (NES) and the J-Anomaly Ridge (JAR) as these localities on the North American margin are still poorly investigated. We obtained a reliable age of 82.39 ± 0.12 Ma (2σ) for the Nashville Seamount (NES) and an alteration age of ca. 76 Ma for the JAR. Our new dates from the New England Seamounts, combined with those available from the Tore–Madeira Rise and SW Portugal, on the Iberia–African margins, confirm an overlapping period of activity around 105-80 Ma on both the North American and Iberian-African margins and the adjacent oceanic basins. Plate kinematic reconstructions indicate that these magmatic occurrences were located within a ~1000 km radius within the yet narrow Atlantic Ocean. The J-Anomaly Ridge samples were most likely formed at the mid-Atlantic ridge around ~120 Ma. The Sr-Nd-Pb initial isotopic ratios from the New England seamounts show similarities with the chemical signature of the Tore–Madeira Rise and, to a lesser extent, SW Portugal. Moreover, New England Seamounts display a trend toward EMI isotopic end-member, similar to those documented in at the Late Cretaceous Godzilla seamount on the Tore–Madeira Rise and sills from ODP Site 1276. The shared chemical signature is distributed across a torus-shaped area of ~2000 × 2000 km at a near-fixed location on Earth and is not temporally-controlled, suggesting a large-scale chemical anomaly in the shallow mantle. Therefore, geochronological, geochemical and plate reconstructions imply a large-scale, anomalously fertile mantle source that generated widespread magmatism during the Late Cretaceous in the northern Central Atlantic.
|
|
