Construction of a crustal balanced cross-section across the Pyrenean chain shows a minimum shortening of 147 km, 112 km of which are related to stacking of basement thrust sheets in the southern Pyrenees. Metamorphic conditions of the basement rocks, as well as thrust geometry, indicate the maximum depth for the detachment level to be at 15 km. In the restored cross-section, the upper crust is 110 km longer than the lower layered crust. The lower crust was subducted together with the lithospheric mantle into the asthenospheric mantle and has not been imaged by geophysical data probably because an increase of density through eclogitic meta-morphism. The upper crust constitutes an orogenic lid mainly deformed by thrust structures. The balanced cross-section has been constrained by the ECORS deep reflection seismic profile as well as detailed surface data and available commercial seismic and oil well data. The restored cross-section provides a better picture of the middle Cretaceous combined strike-slip and extensional fault system as well as of the Hercynian crust. Hercynian geological features have been used as an additional tool for the restoration of the basement thrust sheets.

Evolution of a continental collision belt: ECORS-Pyrenees crustal balanced cross-section

Summary This overview summarizes aspects of 150 years of research in Alpine tectonics and in particular introduces the tectonic setting for the more detailed papers in this volume. The Alpine Mesozoic ocean, Tethys, formed as a large elongate pull-apart basin in the Jurassic, as a consequence of the opening of the Atlantic and of the movement of Africa towards the east relative to a fixed Europe. The NNE trending Tethys was bounded by WNW trending transforms, by the European/Iberian margin in the W and by the Adriatic promontory of Africa in the E, and its shape determined the present day configuration of the arcs of the Alpine chain. The closing of this ocean and the collision tectonics began during the Cretaceous, as Africa moved to the NE relative to Europe and as the N Atlantic gradually opened, to drive Iberia and the southern part of the European plate to the E. Subduction of oceanic crust and adjacent continental crust led to high pressure metamorphism of Cretaceous age. Ophiolites were obducted over the southern continental margin, but after collision the shear sense reversed so that the Austro-Alpine nappes of the African Adriatic promontory overthrust Europe in a WNW direction. During the main Tertiary deformation the overall anticlockwise rotation of Africa led to a change-over from N to NW and WNW-directed collisional structures. The E-W striking sector of the Alps in Switzerland and Austria is therefore a diffuse transpressive dextral shear belt, approximately reworking the northern transform boundary of Tethys, modifying it by compression related to the rotation of the African Adriatic promontory. Approximately 250 km of European lithosphere were involved in the building of the western Alps. As Alpine nappes consist largely of rock material confined to the upper crust, a large amount of lower crust and lithospheric mantle of the two continental blocks must be duplicated and/or subducted during the Alpine collision history.

Alpine tectonics — an overview

Surface and subsurface data are combined to construct a crustal-scale cross section of the western central Pyrenees (France and Spain) at the boundary between the European and Iberian plates. The position of Moho reflections in the ECORS-Arzacq reflection profile suggests a tectonic wedge of European crust and upper mantle had indented the Iberian plate at lower crustal levels. The European wedge is overlain by an upper, Iberian wedge thus constituting a double (stacked) wedge geometry. The upper wedge was delaminated and deformed giving rise to the Pyrenean orogenic prism, manifested as a bivergent fan in upper crustal levels. The underthrust lower Iberian plate has been imaged to depths of 55–60 km, but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km. Total orogenic contraction calculated from surface structures is about 75–80 km, which was accomplished between the latest Cretaceous and the early Miocene at an averaged rate of 1.2 mm/yr. Consistent with these moderate values, exhumation of the orogen is much less than in the more shortened eastern parts of the range. Paleozoic basement and preorogenic Mesozoic rocks are little eroded, and much of the exhumation involved cannibalization of early foreland basins, which once covered the entire, poorly emergent orogen at this transect. This resulted in a continuous process of sediment recycling and, coupled with a considerable lateral arrival of material, a bulk negative erosion-sedimentation budget.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98TC00561

Crustal structure and orogenic material budget in the west central Pyrenees

Summary Collision mountain belts have recently been interpreted as being large scale stacked sedimentary basins, where the wholesale reactivation of pre-existing normal faults exerts the primary control on orogenic style. This model is explored here using examples from the Western Alps. The use of stratigraphic separation across faults, in the absence of corroborative sedimentological data, provides an ambiguous criterion to determinate fault reactivation. Variations between ‘compressional’ and ‘extensional’ stratigraphic separations across the Frontal Pennine thrust are more likely to be due to regional unconformity patterns developed in lower Tertiary times rather than normal fault reactivation along the eastern margin of the external zones. Mesozoic-Tertiary basin structure has been important in controlling the sites of major thrust ramps where stratigraphic horizons suitable for activation as thrust detachment zones have been offset. Examples include the thrust front in the Jura (Triassic detachment dropped to W by faults bounding the Bresse basin) and Vercors (basement uplifted to W at Faille de l’Isere, bounding the Mesozoic sub-Alpine basin to W). Buttressing structures, where thrust displacement is converted into vertical pure shear, may indicate buried normal faults but can occur at either hinterland or foreland-directed basin faults. The overall structural style in the sub-Alpine thrust belt indicates detachment between basement and cover with basement involvement along the Sole thrust which carries the external basement massifs. There is no indication from surface geology that this thrust originates from reactivation of a Mesozoic basin fault although this process may have occurred at depth. Similar styles of detachment-dominated thrusting with large horizontal relative to vertical displacements also characterize internal Alpine structure. Preliminary results from the ECORS-CROP deep seismic reflection profile across the Western Alps support the detachment thrusting model although they do not rule out minor normal fault reactivation.

The influence of pre-existing basin structure on thrust system evolution in the Western Alps

Abstract During Alpine collision the western margin of Tethys was uplifted on large-scale thrust zones, to preserve and give excellent 3D exposures of Mesozoic fault geometries. The faults are particularly well exposed along the margins of the Belledonne and Pelvoux basement massifs, east of Grenoble. Jurassic normal faults were in places reworked and the basins partially inverted during Cretaceous to Miocene compression. They were subsequently locally reworked by an important phase of late Alpine extension. Both listric and straight (rotational) normal faults occur in Variscan granitic basement and Mesozoic cover. Several orders of synthetic and antithetic faults can be mapped, recording strains which are probably related to bends or kinks in the surfaces of the master faults. The extension directions vary, apparently related to variations in anisotropy of the Variscan basement, in particular to the trends of Variscan mylonites. In some regions there was apparently simultaneous extension on two orthogonal fault orientations. On the northern margin of the Pelvoux Massif, late Alpine extensional faults rework both Variscan fabrics in the basement and Alpine mylonites in the cover, producing a large extensional duplex whose roof is a low-angle fault zone in schistose Lias. The late Alpine extension may be caused by gravitational collapse of the thickened crust, or by regional continental extension as part of the opening of the Gulf of Lyon and the Rhone—Bresse Basins. Pulses of compressional tectonics occurred in the Middle Cretaceous, latest Cretaceous—Early Palaeogene, Eocene—Oligocene and Miocene. During each pulse the deformation occurred principally on foreland-propagating fold and thrust sequences but there are important break-back thrusts, e.g. along the Frontal Pennine Zone, where the thrusts slice across already-sheared and back-tilted rocks to give apparent extensional cut-off relationships. The Alpine compression reactivated Mesozoic faults in basement and syn-rift sediments, deforming the syn-rift graben fill by tight upright folds and back-thrusts. NW-trending Mesozoic lateral ramps gave the basin margin a tooth-like geometry, which on compression did not fit back into the sockets of the opposite margin, causing material to be squeezed out laterally as well as vertically. Such variations in thrust displacement, a form of continental escape similar to large scale indentation tectonics, were partially responsible for the development of the Alpine arc.

Extensional structures and their tectonic inversion in the Western Alps

Premiers résultats de la traversée des Alpes Occidentales par sismique réflexion verticale (programme ECORS-CROP)

Studi geologici nel versellese e nella valle strona

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

R. Sacchi

Author Tools

Chat about Author

Papers

Premiers résultats de la traversée des Alpes Occidentales par sismique réflexion verticale (programme ECORS-CROP)

Studi geologici nel versellese e nella valle strona