/pdf/reconciling-plate-tectonic-reconstructions-of-alpine-tethys-1do3i5vm2t.pdf

Reconciling plate-tectonic reconstructions of Alpine Tethys with the geological–geophysical record of spreading and subduction in the Alps

A complete Alpine cross section integrates numerous seismic reflection and refraction profiles, across and along strike, with published and new field data. The deepest parts of the profile are constrained by geophysical data only, while structural features at intermediate levels are largely depicted according to the results of three-dimensional models making use of seismic and field geological data. The geometry of the highest structural levels is constrained by classical along-strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units. Because the transect is placed close to the western erosional margin of the Austroalpine nappes of the Eastern Alps, it contains all the major tectonic units of the Alps. A model for the tectonic evolution along the transect is proposed in the form of scaled and area-balanced profile sketches. Shortening within the Austroalpine nappes is testimony of a separate Cretaceous-age orogenic event. West directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the Meliata-Hallstatt Ocean further to the east. Considerable amounts of oceanic and continental crustal material were subducted during Tertiary orogeny, which involved some 500 km of N-S convergence between Europe and Apulia. Consequently, only a very small percentage of this crustal material is preserved within the nappes depicted in the transect. Postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments, both detachments nucleating at the interface between lower and upper crust. Large scale wedging of the Adriatic (or Apulian) lower crust into a gap opening between the subduced European lower crust and the pile of thin upper crustal flakes (Alpine nappes) indicates a relatively strong lower crust and detachment between upper and lower crust.

/pdf/geophysical-geological-transect-and-tectonic-evolution-of-46ydfb6bel.pdf

Geophysical‐geological transect and tectonic evolution of the Swiss‐Italian Alps

https://doc.rero.ch/record/4946/files/1_mosar_sop.pdf

Subduction and obduction processes in the Swiss Alps

Reconstructions of the Tethyan realm have been a matter of debate for a long time. Controversies spring usually from a lack of well constrained geological data which can be interpreted in different ways, or, from a lack of constraints on the plate tectonics framework. The western Alps region tends to escape these shortcomings due to a wealth of geological data regarding for examples the rifting and spreading of the Alpine Tethys and its closure, the formation of the Alpine orogenic wedge and accompanying foreland basins, through precise datation of these many events. The larger plate tectonic framework is also well constrained through precise positioning, at least since the Jurassic, of the main plates surrounding the western Alpine Tethys domain, such as the European and African plates, but also the Iberic and Adria micro-plates and the Alboran fragments. Therefore, the Western Alps and surrounding regions represent a key-stone for the western Tethys reconstruction. A detail account of the geological evolution along a western Swiss Alps transect is presented here and confronted to the plate tectonic models derived from a larger western Tethys data base.

/pdf/western-alps-geological-constraints-on-western-tethyan-1n9j0q3ox4.pdf

Western Alps geological constraints on western Tethyan reconstructions

Palinspastic map reconstructions and plate motion studies reveal that switches in subduction polarity and the opening of slab gaps beneath the Alps and Dinarides were triggered by slab tearing and involved widespread intracrustal and crust–mantle decoupling during Adria–Europe collision. In particular, the switch from south-directed European subduction to north-directed “wrong-way” Adriatic subduction beneath the Eastern Alps was preconditioned by two slab-tearing events that were continuous in Cenozoic time: (1) late Eocene to early Oligocene rupturing of the oppositely dipping European and Adriatic slabs; these ruptures nucleated along a trench–trench transfer fault connecting the Alps and Dinarides; (2) Oligocene to Miocene steepening and tearing of the remaining European slab under the Eastern Alps and western Carpathians, while subduction of European lithosphere continued beneath the Western and Central Alps. Following the first event, post-late Eocene NW motion of the Adriatic Plate with respect to Europe opened a gap along the Alps–Dinarides transfer fault which was filled with upwelling asthenosphere. The resulting thermal erosion of the lithosphere led to the present slab gap beneath the northern Dinarides. This upwelling also weakened the upper plate of the easternmost part of the Alpine orogen and induced widespread crust–mantle decoupling, thus facilitating Pannonian extension and roll-back subduction of the Carpathian oceanic embayment. The second slab-tearing event triggered uplift and peneplainization in the Eastern Alps while opening a second slab gap, still present between the Eastern and Central Alps, that was partly filled by northward counterclockwise subduction of previously unsubducted Adriatic continental lithosphere. In Miocene time, Adriatic subduction thus jumped westward from the Dinarides into the heart of the Alpine orogen, where northward indentation and wedging of Adriatic crust led to rapid exhumation and orogen-parallel escape of decoupled Eastern Alpine crust toward the Pannonian Basin. The plate reconstructions presented here suggest that Miocene subduction and indentation of Adriatic lithosphere in the Eastern Alps were driven primarily by the northward push of the African Plate and possibly enhanced by neutral buoyancy of the slab itself, which included dense lower crust of the Adriatic continental margin.

/pdf/reconstructing-the-alps-carpathians-dinarides-as-a-key-to-vlcko8xz3m.pdf

J.C Hunziker

Papers

Tectonometamorphic history of the Ivrea Zone and its relationship to the crustal evolution of the Southern Alps