AlpArray is changing notions of lithospheric subduction along the Alps and its effects on orogeninc lithosphere. Teleseismic V_p tomography reveals a slab of European lithosphere that is largely detached at and below 150 km in the Western Alps. Only in part of the Central Alps is the slab still attached, possibly reaching down to the mantle transition zone, where it appears connected to subducted remains of Alpine Tethys. SKS directions beneath the Alps suggest that asthenosphere not only flowed passively around the sinking slab, but may have induced the anomalous northward dip of the detached slab segment beneath the Eastern Alps.

The structure of the orogenic lithosphere differs profoundly along strike of the Alps, as revealed by local earthquake tomography, ambient-noise studies, as well as S-to-P receiver-functions and gravity studies: In the Central Alps where the slab is still attached, the exhumed retro-wedge of the orogen overrides a wedge of Adriatic lower crust. In the Eastern Alps where the slab has detached, exhumation is focused in the orogenic core (Tauern Window) north of and above bulged lower crust of presumed Adriatic origin. This indicates decoupling at the base of qtz-rich, presumably hydrous intermediate crust to accommodate coeval Miocene N-S shortening, orogen-parallel thinning and eastward extrusion of orogenic lithosphere.

We propose a new model for Alpine orogenesis that invokes changing wedge stability and migrating subduction singularities above the delaminating and detaching Alpine slab in the east to explain east-west differences in Oligo-Miocene structure, magmatism, erosion and sedimentation in peripheral Alpine basins.

Orogens in the Alpine-Himalayan collision zone (AHCZ) exhibit characteristic diffused seismicity compared to the stable continental interiors. Interestingly, they also have a thicker-than-average silica-rich upper crust and total crustal thickness, while their lithosphere thickness is similar to that of stable continental interiors (e.g., Tibet, Zagros). These observations provide a metric for the lithospheric-scale geological inheritance, the role of which we aim to understand in continental lithosphere dynamics over seismic and geologic timescales. To achieve this understanding, we use data-driven modelling to compute the present-day thermomechanical state of the AHCZ lithosphere.

Our results indicate the existence of a critical crustal thickness, which is thermodynamically controlled by the internal energy and chemical composition of the crust and is similar to the global average of continental crust thickness. Orogenic lithospheres with thicknesses above this critical value possess higher potential energy and are weakened by the internal energy from heat-producing elements, whereas continental interior lithospheres with thicknesses close to the critical crustal thickness are stronger. Weaker orogenic lithospheres respond via dissipating this energy in a diffused deformation mode, leading to zones of deformation in contrast to focused deformation at the plate-boundaries. The observed crustal differentiation in the AHCZ could be understood as perturbations to the critical crustal thickness caused by plate-boundary forces. The dynamic evolution of these perturbations indicates that the critical crustal thickness is a stable fixed-point attractor in the evolutionary phase-space.

To relate Intraplate volcanism to upper mantle structure, we investigate small-scale structural-variations of the lithosphere-asthenosphere beneath the Circum-Mediterranean using regional high-resolution 3-D surface-wave tomography. The imaged low shear-wave velocities (Vs<4.2 km/s) between depths of ~70-300 km indicate the presence of nine shallow asthenospheric volumes (SAVs) across the Circum-Mediterranean upper mantle forming a partly interconnected belt and separated only by high velocity slabs and thickened lithosphere. Integrated geophysical-petrological modelling for 14 representative locations, yields estimates of the lithospheric thickness and the upper mantle geotherm and confirms the presence of thin lithosphere (<80 km) above areas of anomalously warm SAVs (>1300°C).

We distinguish between Intraplate, Mixed-origin and Subduction-related volcanism in the Circum-Mediterranean during the last 70 Ma and find a remarkable colocation between the SAVs and Cenozoic Intraplate and Mixed-origin volcanic provinces (IMVPs). Moreover, the lateral distance from any shallow asthenosphere to the closest neighboring volcanic province is, on average, as low as 100 km, with a maximum distance of 350 km, indicating a dense network of IMVPs above SAVs. By contrast, IMVPs are completely absent in areas of thick mantle lithosphere.

We relate origin of the SAVs either to asthenospheric upwelling caused by slab-rollback and back-arc extension (Aegean-Anatolian, Pannonian, Moesian, Western Mediterranean SAVs) or to thermal erosion of the lithosphere partly coupled with continental rifting (Adriatic, Central European, North African, Middle East SAVs), respectively. The oldest ages of the IMVPs in the Circum-Mediterranean indicate that the development of the current SAVs started at about ~60-70 Ma ago and accelerated in Neogene.

Imaging the deep Earth structures is conventionally carried out using earthquake recordings. However, the resolving capability of such techniques (e.g., SS precursors and receiver function analysis) is often limited by the uneven spatial distribution of earthquake events and the high complexity of earthquake rupture processes. Recent advances in passive noise interferometry demonstrated the possibilities of recovering body waves from noise correlations, opening up new prospects for imaging the deep earth.

In this study, we map the mantle transition zone (MTZ) discontinuities beneath South- Central Europe using P-wave reflection phases recovered from noise correlations. We analyze up to four years of seismic noise recordings from 900 broadband stations in the study area. By stacking noise correlations in selected summer months, we significantly improved the retrieval of typically low-amplitude body-wave reflection phases in the light of a quiet surface-wave environment and sufficient noise body-wave illumination from deep paths. We obtain reliable P-wave reflections associated with the 410-km and 660-km discontinuities in the period band of 4-10 s. These short-period reflections reveal clear lateral depth variations of the two discontinuities, indicating a complex MTZ arrangement in the greater Alpine region that is related to both present and past tectonic regimes. Our imaging method shows its potential for general applications in studying deep-earth discontinuities.