First interpretation of mantle structure in the Alps-Apennines-Carpathian-Pannonian region from teleseismic Vp studies

Geowissenschaften, Ruhr-Universität Bochum, Germany; Geowissenschaften, Freie Universität Berlin, Germany; Institut für Geophysik, ETH-Zürich, Switzerland A pattern of teleseismic Vp anomalies in the greater Alpine area reflect asymmetrical mantle structure in the Alps as well as pronounced orogen-parallel variations. The foreland of the Western and Central Alps shows layered +Vp and -Vpanomalies that extend from the Variscan belts to beneath the Alpine orogenic front. The base of the lower -Vp layer lies at a depth of c. 180 km. However, below the Tauern Window and to the east, this layering is less pronounced and subhorizontal, with an undefined base. In the Eastern Alps, the +Vp anomalies define an ultrathin (≤ 50 km) lithospheric lid underlain by shallow -Vp anomalies trending E-W, parallel to the direction of eastward-lateral motion of the AlCaPa unit into the Pannonian Basin. Isolated +Vp anomalies underlie the Eastern Alps at c. 200 km depth. South of the Alps the Adriatic lithosphere is some 80-100 km thick and underlain by variably strong -Vp anomalies. No slab anomaly is detected beneath the northern Dinarides. We interpret the Vp anomaly pattern in the Western and Central Alps to indicate SSE-directed subduction and partial detachment of a thick, compositionally heterogeneous European tectosphere comprising inherited (Variscan?) Vp anomalies. +Vp anomalies beneath the Alps represent subducted lithosphere in various stages of tearing and delamination, with complete delamination east of the western Tauern Window. Shallow -Vp anomalies in this domain document asthenospheric upwelling which facilitated crust-mantle decoupling during Miocene escape of AlCaPa. The slab anomaly beneath the northern Apennines is detached from its foreland and hangs subvertically.