SPP2 Project - Switching pro- and retro-wedges in the Eastern Alps and their peripheral basins - clues to a change in subduction polarity?

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This project will meet the challenge of determining whether or not a Neogene switch in subduction polarity occurred beneath the Eastern Alps. Further, it will answer the question of how Neogene motion of the indenting Adriatic plate was transferred to the Alpine orogenic crust and will identify the interactions between indentation, slab motions and the dynamics of the Molasse and Veneto (eastern Po) Basins, respectively, north and south of the Alpine Orogen.This will be done by using the structure and basin histories of the Alpine orogen as proxies for subduction polarity. Such a switch is predicted to effect change in the behaviour of the northern orogenic front from pro-wedge type (episodic advance by alternating in- and out-of-sequence thrusting) to retro-wedge type (slower advance, alternating in-sequence thrusting and stagnation). This contrasting behavior is expected to be reflected in the amount and nature of clastic deposits in the Molasse Basin. The transition of the northern Alpine front from pro- to retro-wedge behavior is arguably manifested by stagnation of the thrust front at ~21 Ma during prolonged subsidence of the eastern Molasse Basin until ~16 Ma. Along the southern Alpine front, retro-wedge behaviour may have changed to pro-wedge behaviour with the onset of Neogene thrusting and deformation of proximal parts of the Veneto Basin at 21-22 Ma. The project combines 3 work packages using state-of-the-art seismology, basin analysis and structural geology. The seismological work package will (re)process seismic reflection data from the TRANSALP experiment using cutting-edge techniques. Multi-dimensional coherence analysis will drastically reduce noise and improve subsurface reconstructions with a clearer definition of geologically relevant signatures. The basin analysis work package will use industry seismics and borehole data to reconstruct the structural of the northern orogenic front, the Tertiary subsidence history of the eastern Molasse Basin along and across its strike, and variations in sedimentation patterns next to the orogenic front. The structural geology work package will use these new images as well as those emerging from the EASI and SWATH-D experiments to construct and tectonically balance new integrated geological-geophysical cross sections reaching from the Molasse Basin through the basement core of the Eastern Alps to the Veneto Basin in the south. Deliverables include (1) a 3D high-resolution image of faults beneath the Tauern Window area that partitioned strain during Adriatic indentation and lateral escape; (2) a 4D model of the eastern Molasse Basin that documents advances and retreats of thrusting along the orogenic front, from the Central-Eastern Alps transition in the west to the Alps-Carpathians junction in the east; (3) an integrated 4D model of the Eastern Alps, from slab tearing and breakoff to Adriatic indentation.