Alpine tectonics — an overview

Abstract

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.

Early exhumation of underthrust units near the toe of an ancient erosive subduction zone: A case study from the Northern Apennines of Italy

“…In the Northern Apennines, the Late Cretaceous convergence of the Adria-Africa plate and the European plate led to the subduction of a western branch of the Tethys ocean (Coward and Dietrich, 1989) and the buildup of an oceanic accretionary prism, called the Ligurian accretionary prism or the Ligurian Units (Principi and Treves, 1984;Treves, 1984;Marroni et al, 2010;Molli and Malavielle, 2011).…”

Pacific-type Orogens

“…9 Tectonic development of Himalayan orogenic belt after Kaneko, 1997 (Coward and Dietrich, 1989;Maruyama et al, 1996) (Coward and Dietrich, 1989;Maruyama et al, 1996) . N-S cross-section of the Alpine orogen shows the structural intermediate of the Penninic nappe with the Alpine peridodite surrounded at the top and bottom by unmetamorphosed Austro-alpine and Helvetic units.…”

Introduction: the deformation of continental crust and Mike Coward's impact on its understanding

“…The implications for crustal balancing are recognized in the region (e.g. Coward & Dietrich 1989). However, the lessons have barely been applied to the restacked continental margin in the Himalayas, notwithstanding many attempts at crustal-scale thrust interpretations (discussed above).…”