Mapping and the construction of balanced cross-sections reveal dextral rotation in addition to N-S contraction during the late middle to late Miocene Jura phase both at the northern and the southern front of the Central Alps (Jura and Lombardic Southern Alps, respectively). These rotations may be ascribed to one and the same shallow domain or sublid, rotated clockwise around a pivot somewhere at the southwestern end of the Aar massif. In a crude first approximation model the sublid may be considered rigid, although the data indicate differential rotations and longitudinal stretching within the lid. The eastern boundary of the sublid crosses the Alps at the Giudicarie-Brenner line, which, according to very recent data, in the Jura phase formed a kinematically linked system, whereas from Innsbruck to the northwest it is postulated to join, as a diffuse or accommodation zone, the eastern tip of the Jura. In the southwest, the Lombardic thrusts enter into the interior of the Western Alps. From there to the southwestern end of the Jura the lid boundary is tentatively chosen arbitrarily to pass somewhere near the northern end of the Belledonne Massif. A similar sublid, though less well substantiated, may comprise the Tauern and the Venetian Southern Alps. The rotational components are superimposed on elements of internal strain, particularly transverse contraction and longitudinal stretching due to simple dextral shear and lateral escape. The model of dextrally rotating sublids pulls together a number of hitherto unexplained structures and opens new perspectives on such recalcitrant problems as the eastward disappearance of the Jura and the Adige embayment in the Southern Alps. Dextral rotation of such shallow sublids may be considered to constitute ''mode 1'' of the dextral component at the Europa-Adria plate boundary. There is also a ''mode 2'' that affects its deep parts. At the surface, its manifestation is a dextral belt of en ¿chelon folds and pull-apart domains that crosses the sublids diagonally. It consists of the Massifs line in the west and the Neo-Pustertal line in the east. They approximately join in the Brenner area, where they cross and interfere with the sublid boundaries. The combined Massifs-Pustertal line describes an arcuate partial northern boundary of the Adriatic plate with an apparent center of sinistral rotation in central Italy. This sinistral rotation may be responsible for the contractional features in the southern part of the western Alps which cannot be accounted for by SE-NW Adria-Europa convergence. It could have caused the development of the fold and thrust belts of Sisteron, Castellane and Nice. These arcs, in turn, suggest the action of more or less independent shallow sublids also in this part of the Alps. ¿ American Geophysical Union 1996 |