Continental crust subjected to horizontal contraction in convergent settings deforms in a variety of styles. In many instances, it is useful to consider the deforming crustal sections in terms of crystalline basement rocks underlying incipiently undeformed sedimentary strata. Three deformation styles are commonly found in such settings. The structural style referred to as thin-skinned tectonics encompasses a stack of thrust sheets composed of non- or weakly metamorphic sedimentary rocks. The associated thrust faults usually level off in a mechanically weak décollement horizon along which a substantial amount of displacement occurs in the course of the formation of the fold-and-thrust belt. Thrust faults may also cut down into the crystalline basement and level off a few kilometers beneath the basement-cover interface. The term basement-involved thin-skinned tectonics is proposed to describe this style of continental contraction. This style, too, is characterized by stacks of thrust sheets. In many cases however, such nappe stacks are overprinted by pervasive folding of a crust thermally weakened by magmatic activity or regional burial metamorphism. Thick-skinned tectonics seems less common. This style implies that thrust faults cut across the entire upper crust (and possibly the lower crust). The associated continental contraction is smaller, and the ensuing deformation is characterized by warping of the basement-cover interface. Displacements accumulated in a major basal detachment horizon may connect into mantle by means of a subduction zone. However, under elevated temperatures, pervasive deformation of the hanging wall and footwall rocks may compensate large displacements over relatively short distances. Thin-skinned fold-and-thrust belts are common on both sides of collisional orogens. Noncollisional orogens tend to be more asymmetric.

Abstract The Alps and Western Carpathians constitute that part of the Alpine-Mediterranean orogenic belt which advances furthest to the north into Central Europe. They were formed by a series of Jurassic to Tertiary subduction and collision events affecting several Mesozoic ocean basins, continental margins, and continental fragments. The Western Alps form a pronounced, westward-convex arc around which the strike of the tectonic units changes by almost 180° ( Fig. 18.1 ). The Western Carpathians are a northward-convex arc of similar size but with minor curvature. The two arcs are connected by an almost straight, WSW-ENE striking portion including the Eastern Alps Stresses produced by tectonic processes in the Alps also influenced the tectonics of large parts of central and northern Europe, leading, for example, to basin inversion and strike-slip faulting. In this chapter, we will discuss the present-day structure of the different tectonic units in the Alps and Western Carpathians in relation to their palaeotectonic history in order to illustrate the plate tectonic evolution using geological data. Many tectonic problems of the Alps and Western Carpathians are still unsolved, although dramatic progress has been made, especially over the last c. 20 years. Therefore, some of the interpretations presented below are still controversial and do not always express the opinion of all three authors. Given that the main theme of this book is Central Europe, the Southern and Western Alps are discussed in less detail than those parts of the Alps which belong to Central Europe: the Central Alps, the Eastern Alps and the Western Carpathians.

Abstract During Europe–Adria collision in Tertiary times, the Monte Rosa nappe was penetratively deformed in several stages after an eclogite-facies pressure peak: (1) top-to-the-NW thrust shearing (Mattmark phase, after 40 Ma); (2) orogen-parallel, top-to-the-SW extensional shearing and folding (Malfatta phase); (3) orogen-perpendicular, top-to-the-SE extensional shearing and folding (Mischabel phase, before 30 Ma); and (4) large-scale, upright, SE-vergent folding (Vanzone phase, c . 29–28 Ma). Structural analysis and neutron texture goniometry of quartz mylonites show that the Stellihorn shear zone in the Monte Rosa nappe accommodated a complex and multidirectional sequence of shearing movements during the Mattmark, Malfatta and Mischabel phases, and was folded in the Vanzone phase. In the tail-shaped eastward prolongation of the Monte Rosa nappe in the Southern Steep Belt of the Alps, both dextral and sinistral mylonites (Olino phase) were formed during and after the formation of the Vanzone fold, reflecting renewed orogen-parallel (SW–NE) extension contemporaneous with NW–SE shortening from c . 29 Ma onward. A similar sequence of deformation stages was identified in the Adula nappe at the eastern border of the Lepontine metamorphic dome. Important consequences arise for the Insubric fault at the southern border of the Lepontine dome: (1) the NW- to N-dipping orientation of the Insubric fault is not a primary feature but resulted from rotation of an originally SE-dipping shear zone after c . 30 Ma; and (2), the strong contrast in metamorphic grade across this fault (upper amphibolite facies to the north versus anchizone to the south) results from north-side-up faulting coupled with orogen-parallel extension of the northern block (Lepontine dome), while no such extension occurred in the southern block (Southern Alps). Extension in the northern block started in the Malfatta phase and continued in the Mischabel phase when the foliation in the area which later became the Southern Steep Belt still dipped towards south. During Vanzone/Olino deformation, further unroofing and uplift of the Lepontine dome relative to the South Alpine block took place while the Southern Steep Belt was progressively rotated into its present, overturned position, changing its character from a normal fault into a backthrust. Complex deformation paths in the Southern Steep Belt resulted from the combination of extension of the northern block with strike-slip motion along the Insubric fault.