| 1. |
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| 2. |
- Cadenas, Patricia, et al.
(författare)
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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
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Ingår i: Bulletin de la Société Géologique de France. - : EDP Sciences. - 0037-9409 .- 1777-5817. ; 192
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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.
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| 3. |
- Frasca, Gianluca, et al.
(författare)
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A kinematic reconstruction of Iberia using intracontinental strike-slip corridors
- 2021
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Ingår i: Terra Nova. - : John Wiley & Sons. - 0954-4879 .- 1365-3121. ; 33:6, s. 573-581
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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.
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| 4. |
- Lehujeur, Maximilien, et al.
(författare)
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Three-dimensional shear velocity structure of the Mauleon and Arzacq Basins (Western Pyrenees)
- 2021
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Ingår i: Bulletin de la Société Géologique de France. - : EDP Sciences. - 0037-9409 .- 1777-5817. ; 192
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Tidskriftsartikel (refereegranskat)abstract
- We present a 3-D shear wave velocity model of the Mauleon and Arzacq Basins from the surface down to 10 km depth, inverted from phase velocity maps at periods between 2 and 9 s. These phase velocity maps were obtained by analyzing coherent surface wave fronts extracted from ambient seismic noise recorded by the large-N Maupasacq seismic array with a matched filtering approach. This new model is in good agreement with a local earthquake tomography study performed on the same acquisition dataset. Our passive imaging models reveal the upper crustal architecture of the Mauleon and Arzacq Basins, with new details on the basement and its relationship with the overlying sedimentary cover. Combining these new tomographic images with surface and subsurface geological information allows us to trace major orogenic structures from the surface down to the basement. In the basin, the models image the first-order basin architecture with a kilometric resolution. At depth, high velocity anomalies suggest the presence of dense deep crustal and mantle rocks in the hanging wall of north-vergent Pyrenean Thrusts. These high velocity anomalies spatially coincide with a positive gravity anomaly in the western Mauleon Basin. In addition, our models reveal major changes from the Chainons Bearnais to the western Mauleon Basin across a set of orogen-perpendicular structures, the Saison and the Barlanes transfer zones. These changes reflect the along-strike variation of the orogenic evolution that led to the preservation of the former rifted domain and its underlying mantle in the orogenic wedge of the Western Pyrenees. We discuss the implications of these results for the 3-D architecture of the Mauleon Basin and its underlying basement.
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| 5. |
- Lescoutre, Rodolphe, et al.
(författare)
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Large-scale, flat-lying mafic intrusions in the Baltican crust and their influence on basement deformation during the Caledonian orogeny
- 2022
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Ingår i: Geological Society of America Bulletin. - : Geological Society of America. - 0016-7606 .- 1943-2674. ; 134:11-12, s. 3022-3048
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Tidskriftsartikel (refereegranskat)abstract
- The Fennoscandian Shield in central Sweden displays a complex structural and compositional architecture that is mainly related to the Proterozoic history of the Baltica paleocontinent. In its western parts, the Precambrian basement is covered by the allochthonous rocks of the Caledonide orogen, and direct information about the underlying crust is restricted to a few unevenly distributed basement windows in western Sweden and Norway. In this study, we use preliminary results from the second borehole of the Collisional Orogeny in the Scandinavian Caledonides project (COSC-2), new gravity data, forward gravity, and magnetic modeling and interpretation of seismic reflection profiles to assess the 3-D architecture of the basement. Our results reveal a wide (∼100 km) and dense network of mainly flat-lying and saucer-shaped dolerites intruding the volcanic and granitic upper crustal rocks of the Transscandinavian Igneous Belt. Similar intrusion geometries related to 1.2 Ga dolerites can be recognized in the Fennoscandian Shield. We discuss that the formation of these sill complexes occurred in a lithologically and structurally heterogeneous crust during transtension, which is in disagreement with the current understanding of sill emplacement that involves crustal shortening, layering, or anisotropy of the host rock. Our seismic interpretation and the structural observations from the COSC-2 drilling show that part of the Caledonian-related basement deformation was localized along the margins of the dolerite sheets. We propose that the dolerite intrusion geometry, akin to a flat-ramp geometry, guided the basement deformation during the Caledonian orogeny.
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| 6. |
- Lescoutre, Rodolphe, et al.
(författare)
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Nature, Origin, and Evolution of the Pyrenean-Cantabrian Junction
- 2021
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Ingår i: Tectonics. - : American Geophysical Union (AGU). - 0278-7407 .- 1944-9194. ; 40:5
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the present-day orogenic architecture of the Pyrenean-Cantabrian junction corresponding to a boundary between inverted rift segments using seismic interpretation, field data, and borehole information. This junction was formerly attributed to a major NNE-SSW striking Pamplona transfer fault segmenting the Basque-Cantabrian and Mauleon basins during both rifting and convergence. Our study shows that the orogenic architecture results from a strong decoupling between the thick-skinned (basement-involved) and the thin-skinned (detached in the Upper Triassic evaporites) modes of deformation. The evaporites decoupling horizon was responsible for the transport and allochthony of the former rift basins over large distances on top of the Basque massifs and the Ebro and Aquitaine foreland basins. A crustal-scale cross-section depicts the allochthony of the Basque massifs forming a crustal wedge over the crusts of Iberian, Ebro, and Eurasian affinity. Three-dimensional analysis of the present-day architecture suggests that two phases of rifting and related basins can be recognized: the Late Jurassic-Barremian and the Aptian-Cenomanian basins. Furthermore, we show that during the Aptian-Cenomanian, the Mauleon and Basque-Cantabrian rift segments spatially overlapped north and south of the Basque massifs and were controlled by WNW-ESE striking extensional faults. These results discard the existence of a major Pamplona transfer fault and argue for NNE-SSW direction of extension during the mid-Cretaceous. This study emphasizes the role of inheritance during rifting and reactivation and provides a new syn-rift template, which controlled the Alpine reactivation. Finally, these results have major implications for the Iberia-Eurasia plate boundary and the kinematics of the North Pyrenean basins.
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| 7. |
- Lescoutre, Rodolphe, et al.
(författare)
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Role of rift-inheritance and segmentation for orogenic evolution : example from the Pyrenean-Cantabrian system
- 2020
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Ingår i: Bulletin de la Société Géologique de France. - : EDP SCIENCES S A. - 0037-9409 .- 1777-5817. ; 191
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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.
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| 8. |
- Lorenz, Henning, Dr. 1972-, et al.
(författare)
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COSC-2 – drilling the basal décollement and underlying margin of palaeocontinent Baltica in the Paleozoic Caledonide Orogen of Scandinavia
- 2022
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Ingår i: Scientific Drilling. - Göttingen : Copernicus Publications. - 1816-8957 .- 1816-3459. ; 30, s. 43-57
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Tidskriftsartikel (refereegranskat)abstract
- Abstract.The Collisional Orogeny in the Scandinavian Caledonides (COSC) scientific drilling project aims to characterise the structure and orogenic processes involved in a major collisional mountain belt by multidisciplinary geoscientific research. Located in western central Sweden, the project has drilled two fully cored deep boreholes into the bedrock of the deeply eroded Early Paleozoic Caledonide Orogen. COSC-1 (2014) drilled a subduction-related allochthon and the associated thrust zone. COSC-2 (2020, this paper) extends this section deeper through the underlying nappes (Lower Allochthon), the main Caledonian décollement, and the upper kilometre of basement rocks. COSC-2 targets include the characterisation of orogen-scale detachments, the impact of orogenesis on the basement below the detachment, and the Early Paleozoic palaeoenvironment on the outer margin of palaeocontinent Baltica. This is complemented by research on heat flow, groundwater flow, and the characterisation of the microbial community in the present hard rock environment of the relict mountain belt. COSC-2 successfully, and within budget, recovered a continuous drill core to 2276 m depth. The retrieved geological section is partially different from the expected geological section with respect to the depth to the main décollement and the expected rock types. Although the intensity of synsedimentary deformation in the rocks in the upper part of the drill core might impede the analysis of the Early Paleozoic palaeoenvironment, the superb quality of the drill core and the borehole will facilitate research on the remaining targets and beyond. Protocols for sampling in the hard rock environment and subsequent sample preservation were established for geomicrobiological research and rock mechanical testing. For the former, a sparse sample series along the entire drill core was taken, while the target of the latter was the décollement. COSC-2 was surveyed by a comprehensive post-drilling downhole logging campaign and a combined borehole/land seismic survey in autumn 2021. This paper provides an overview of the COSC-2 (International Continental Scientific Drilling Project – ICDP 5054_2_A and 5054_2_B boreholes) operations and preliminary results. It will be complemented by a detailed operational report and data publication.
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| 9. |
- Manatschal, Gianreto, et al.
(författare)
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The role of inheritance in forming rifts and rifted margins and building collisional orogens : a Biscay-Pyrenean perspective
- 2021
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Ingår i: Bulletin de la Société Géologique de France. - : EDP Sciences. - 0037-9409 .- 1777-5817. ; 192
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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.
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