Interfering orogenic processes derived from Alps-Adria interactions

Abstract

Across the world we observe spectacular mountain belts that formed as a result of two colliding plates. Frequently this process is disturbed by the influence of neighbouring geological processes, such as the formation of adjacent mountain belts, adding significant kinematic and geometric complexities to the collisional systems. To understand the relative contributions of the processes involved it is essential to identify the individual interfering processes and to quantify their influence on the evolution of the mountain system. The Eastern Alps (Europe) is such a complex mountain belt and is the prime target of this research with particular interest in the transitions to the neighbouring Dinaric mountain belt and the Pannonian Basin. These transitions provide a unique opportunity to unravel the effects of interfering tectonic processes based on field studies, low temperature geochronology and physical analogue modelling. The geological evolution of the Eastern Alps and Dinarides is largely related to the motion of the African continental plate towards the European plate, with the microcontinent Adria located in between the two. The plate motion of the latter plays a key role in driving the deformation of the Eastern Alps as well as the Dinaric mountain chain. With respect to the Eastern Alps the Adriatic plate is traditionally viewed as a bulldozer that deforms, uplifts and laterally displaces the Eastern Alps. However, we show that these geological processes are also compatible with a tectonic scenario in which the Adriatic plate subducts below the Alps. The subduction also provides a crucial mechanism to create the formation of the Southern Alps, which affects at the same time the geological evolution of the northern Dinarides. The experimental results also strongly suggest that the geological evolution of the Eastern Alps during the last 30 Ma is best explained by phases of oblique and subsequent orthogonal Alps-Adria convergence. This has led to the characteristic deformation patterns of the Eastern Alps: significant crustal thickening in the west and dominant lateral displacements of crustal units in the east. These differences in deformation style are confirmed by our new field observations and low temperature age data which also emphasize a tectonic link to the contemporaneous opening of the Pannonian Basin and associated extension. The data thereby disclose that the coeval collision and extension is critical for the rapid exhumation of metamorphosed rocks around 17 Ma at the transition from the Alps to the Dinarides. At the same time, a recorded phase of accelerated uplift during the last 10 Ma is rather related to the absence of extension in combination with ongoing Alps-Adria collision and deep seated processes. The integrated results of this thesis demonstrate that subduction/collision processes related to Alps-Adria convergence are strongly influenced by neighbouring and far-fielded processes, which has significant implications for the structural and topographic evolution of the studied region.