Reactivation of a hyperextended rift system: the Basque‐Cantabrian Pyrenees case.

This contribution investigates the role of a hyperextended rift system in the formation of the Basque-Cantabrian Pyrenees by discussing their present-day architecture as well as the inherited rift template. Moreover, this work attempts to decipher the onset of reactivation of a hyperextended system and to discuss the related processes during collision. To carry out this study, two regional, crustal-scale cross-sections are presented that provide geological and geophysical information and interpretations across the Central and Western Basque-Cantabrian Pyrenees. Moreover, the two sections are restored back to the Cenomanian and Barremian, corresponding to the end of two independent rift stages respectively. The two sections document different structural styles observed along the orogenic belt. The Central section, involving the Iberian and European plates, shows a thin-skinned structural style, where the Upper Triassic salt acted as a decoupling level between the sedimentary cover and the underlying basement during both extension and reactivation. The Western section, by contrast, crosses only the Iberian plate (i.e., intra-plate section) and displays a hybrid situation showing both thin- and thick-skinned structural styles that were conditioned by the irregular distribution of Triassic salt. Extensional deformation was localised in the north (i.e., Bay of Biscay) and less important in the south. Despite compressional reactivation, the northern part of the Western section preserves its rift template, which provides key insights to restore the internal part of the Central section. In contrast to the Western section, the Central section shows stacked depocenters, resulting from overprinted Mesozoic rift events that had a first order control on the subsequent reactivation. This study corroborates the importance of rift inheritance during the onset of convergence by reactivating the most distal and weak part of the rift system (i.e., serpentinised mantle) before starting the collision phase. A key learning is that the understanding of the nature and distribution of decoupling levels at a crustal scale is fundamental to reconstruct the structural evolution during the formation and reactivation of a hyperextended rift system

The Basque - Cantabrian Pyrenees: report of data analysis

This contribution presents the analysis of a data set that was put together in the PhD thesis of Jordi Miró which is part of the OROGEN Project. The Basque - Cantabrian Pyrenees, that are the focus of this report, have been extensively studied over the last years. Several open debates in the Earth Science community aroused from this realm regarding the formation and reactivation of rift domains and formation of fold and thrust belts. This report summarizes the main tectonic models proposed to explain both the extension and reactivation history over this area and compile a series of data to consider for further discussions and interpretations. This report includes a thematic map of the Basque - Cantabrian Pyrenees showing an analysis of the tectono-stratigraphic evolution of the area. The map covers an area of more than 33 000 km2 and is a graphic representation of the geology of the region based on a large geodatabase including previous published maps and field observations. A composite reflection seismic line crossing the entire Basque - Cantabrian Pyrenees from the Ebro foreland basin to the offshore Landes High is also presented. This section enables to present a continuous dataset along the entire area with the projection of few drill holes, which are presented with the stratigraphic logs following the same tectono-stratigraphic legend obtained from the previous analysis. The main goal of this data report is to provide a coherent and complete dataset to the community, which enables to propose, discuss and test some of the new concepts related to the formation and reactivation of rifted margins. This data report is complementary to the contributions of Lescoutre and Manatschal (2020) and Cadenas et al. (in prep) that are part of the same special volume. Cette contribution présente l'analyse d'une compilation de données acquises par Jordi Miró lors de sa thèse de doctorat qui s'inscrit dans le projet OROGEN. Les Pyrénées Basco-Cantabriques, qui sont l'objet de ce rapport, ont été largement étudiées au cours de ces dernières années. Cette chaîne orogénique a alimenté de nombreuses discussions concernant la formation et la réactivation des domaines de rift ainsi que la formation des chaînes d'avant-pays (« fold-and-thrust belt »). Ce rapport résume les principaux modèles proposés dans la zone d'étude pour expliquer l'évolution tectonique de l'extension à la réactivation, et compile une série de données à prendre en considération pour les discussions et interprétations futures. Il comprend notamment une carte thématique des Pyrénées Basco-Cantabriques montrant les différentes unités tectono-stratigraphiques de la zone. La carte, qui couvre une superficie de plus de 33 000 km2, est une représentation graphique de la géologie régionale s'appuyant sur une large quantité de données comprenant des cartes publiées précédemment ainsi que de nouvelles observations de terrain. Un profile de réflexion sismique composite traversant la totalité des Pyrénées Basco-Cantabriques (du bassin d'avant-pays de l'Ebre au Haut des Landes) est également présentée. Cette section permet de présenter un ensemble de données continu sur toute la zone via notamment la projection des informations extraites des puits de forage tels que les logs stratigraphiques. L'objectif principal de ce rapport est de fournir à la communauté scientifique un ensemble de données cohérent et complet permettant de proposer, discuter et tester certains des nouveaux concepts liés à la formation et à la réactivation des marges hyper-étirées. Ce rapport de données fournit des informations complémentaires aux études disponibles dans cette publication spéciale du projet OROGEN

Role of inheritance during tectonic inversion of a rift system in basement-involved to salt-decoupled transition: Analogue modelling and application to the Pyrenean-Biscay system

The reactivation of former rift systems and passive margins during tectonic inversion and their incorporation into fold-and-thrust belts result in significant structural differences not only between internal and external domains, but also along-strike. The Basque-Cantabrian and Asturian systems are among the best examples to address the role of along-strike changes in rift inheritance since they show a transition from salt to basement-inherited structures divided by a transition zone separating thick- from thin-skinned structural domains. While both domains have been widely described in the literature, the transfer system separating the two has not been sufficiently investigated due to poor seismic imaging and the lack of large-scale outcrops. This contribution aims to address the linkage between basement-controlled (i.e. thick-skinned) and salt-decoupled (i.e. thin-skinned) domains and to describe how deformation is accommodated in the transitional zone between these domains. An experimental programme based on analogue models has been designed that was inspired by the transition from the thin-skinned Basque-Cantabrian Pyrenees to the east to the thick-skinned Asturian Massif to the west. As observed in nature, experimental results show that oblique structures (at low angle with the shortening direction) form in the transitional domain, and their location depends on the linkage of the active structures occurring in both surrounding thick- and thin-skinned domains at different positions. Nevertheless, their orientation and evolution are controlled by the underlying decoupling horizon (i.e. salt). The deformation in the thick-skinned domain produces significant topography over a narrow deformation area due to the lack of effective decoupling levels. On the contrary, deformation in the thin-skinned domain is more distributed due to decoupling, resulting in a wider deformation area of less topography. As a result, syn-contractional sedimentation occurs mainly in the foreland basin in front of the thick-skinned domain, whereas it is observed in the foreland but also in piggyback basins in the thin-skinned domain

Preserved organic matter in a fossil Ocean Continent Transition in the Alps: the example of Totalp, SE Switzerland

International audienc

Constraints on mineralization, fluid‐rock interaction, and mass transfer during faulting at 2–3 km depth from the SAFOD drill hole

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94888/1/jgrb15975.pd

Tectono-stratigraphic evolution and crustal architecture of the Orphan Basin during North Atlantic rifting

The Orphan Basin is located in the deep offshore of the Newfoundland margin, and it is bounded by the continental shelf to the west, the Grand Banks to the south, and the continental blocks of Orphan Knoll and Flemish Cap to the east. The Orphan Basin formed in Mesozoic time during the opening of the North Atlantic Ocean between eastern Canada and western Iberia–Europe. This work, based on well data and regional seismic reflection profiles across the basin, indicates that the continental crust was affected by several extensional episodes between the Jurassic and the Early Cretaceous, separated by events of uplift and erosion. The preserved tectono-stratigraphic sequences in the basin reveal that deformation initiated in the eastern part of the Orphan Basin in the Jurassic and spread towards the west in the Early Cretaceous, resulting in numerous rift structures filled with a Jurassic–Lower Cretaceous syn-rift succession and overlain by thick Upper Cretaceous to Cenozoic post-rift sediments. The seismic data show an extremely thinned crust (4–16 km thick) underneath the eastern and western parts of the Orphan Basin, forming two sub-basins separated by a wide structural high with a relatively thick crust (17 km thick). Quantifying the crustal architecture in the basin highlights the large discrepancy between brittle extension localized in the upper crust and the overall crustal thinning. This suggests that continental deformation in the Orphan Basin involved, in addition to the documented Jurassic and Early Cretaceous rifting, an earlier brittle rift phase which is unidentifiable in seismic data and a depth-dependent thinning of the crust driven by localized lower crust ductile flow

Crustal and basin evolution of the southwestern Barents Sea: from Caledonian orogeny to continental breakup

A new generation of aeromagnetic data documents the post-Caledonide rift evolution of the southwestern Barents Sea (SWBS) from the Norwegian mainland up to the continent-ocean transition. We propose a geological and tectonic scenario of the SWBS in which the Caledonian nappes and thrust sheets, well-constrained onshore, swing from a NE-SW trend onshore Norway to NW-SE/NNW-SSE across the SWBS platform area. On the Finnmark and Bjarmeland platforms, the dominant inherited magnetic basement pattern may also reflect the regional and post-Caledonian development of the late Paleozoic basins. Farther west, the pre-breakup rift system is characterized by the Loppa and Stappen Highs, which are interpreted as a series of rigid continental blocks (ribbons) poorly thinned as compared to the adjacent grabens and sag basins. As part of the complex western rift system, the Bjørnøya Basin is interpreted as a propagating system of highly thinned crust, which aborted in late Mesozoic time. This thick Cretaceous sag basin is underlain by a deep-seated high-density body, interpreted as exhumed high-grade metamorphic lower crust. The abortion of this propagating basin coincides with a migration and complete reorganization of the crustal extension toward a second necking zone defined at the level of the western volcanic sheared margin and proto-breakup axis. The abortion of the Bjørnøya Basin may be partly explained by its trend oblique to the regional, inherited, structural grain, revealed by the new aeromagnetic compilation, and by the onset of further weakening later sustained by the onset of magmatism to the west