Thermo-tectonic evolution of the Dolomites Indenter

Orogens like the Andes or the Himalaya show a notably consistent lithospheric architecture along strike. This consistency is in stark contrast to the distinct lateral variations in crust and lithospheric structure of the Alps that occur over comparably short distances and include, e.g., the subduction polarity of the underlying plates, east-west extensional structures, and the Adriatic indenter. Indenters (strong lithospheric blocks that collide with weaker units) are a main reason for along strike variation in tectonics in many convergent zones and are therefore of special interest. For the Adriatic Indenter the relationship of the deformation in the crust to the dynamics of the underlying mantle remains speculative due to a lack of a comprehensive thermochronological and structural dataset. But the few existing data loosely denote an exhumation pattern not linked to the known fault structures. Our hypothesis is that major changes in the lithospheric structure resulted in regional (large wavelength low magnitude) variations in exhumation rates, the timing of exhumation within the Indenter, and the spatial and temporal shifts of its internal deformation. We propose to collect a new and comprehensive dataset to constrain this history of exhumation and deformation of the eastern Adriatic Indenter (Dolomites Indenter) and to address its relationship to the dynamics of the underlying mantle lithosphere. It is this exhumation record that can provide a solution to the unresolved question: what is the role of deep-seated mantle dynamics in controlling the geometry and internal deformation of the Adriatic Indenter? The latter will be investigated through the proposed physical analogue modelling, which will provide insight in the forcing and associated length-scales of deformation. As part of the international AlpArray initiative, with its focus on seismological investigations of the subsurface, our study provides crucial data for an integrated geodynamic model of Alpine convergence.

The European Eastern Southern Alps have a fascinating geological history. For more than 50 million years, the Adriatic microplate has gradually moved northwards into and on top of Europe. This movement has shaped the European Alps, with rock layers folding, breaking and uplifting. While often thought of as a rigid indenter, the Adriatic plate has undergone significant internal deformation, particularly during the Miocene (23-5 million years). We used the latest low-temperature thermochronology and physical analogue sandbox models to see how the Eastern Southern Alps' unique crustal structure affected its evolution. Geological events before the Alps were formed, including Permian volcanic activity and Jurassic crustal extension, created a patchwork of strong and weak crustal zones. These lateral strength variations were a big factor in how and where the crust deformed later on. Physical analogue sandbox experiments simulating the crust showed that areas with stronger crustal materials (like Permian volcanic rock and carbonate platforms) produced fewer but more pronounced thrust faults. Another important thing we noticed is that newly formed thrust faults tend to change their orientation laterally to follow the boundaries between the weak and strong zones. These outcomes line up well with what we've seen during field work in the Eastern Southern Alps. To put a time constraint on the Alpine and Pre-Alpine deformation events, we used some advanced techniques to figure out when the rocks in this region were heated and cooled over time. By looking at tiny mineral crystals separated from rocks all over the Eastern Southern Alps, we were able to trace a series of heating events caused by volcanic activity, extension of the Earth's crust, and the burial of rocks under thick layers of sediment. One of the main things we found out is that a Triassic volcanic event around 240 million years ago caused temperatures underground to rise a lot. This affected the whole region, not just the areas near the actual volcanoes. Later, as the Earth's crust cooled and stabilised, these volcanic and tectonic events left a patchwork of thermal signatures in the rocks. In the last 20 million years, rapid movements along the aforementioned thrust faults brought the before buried rocks to the surface. The results of this study show how massively earlier geological events influence the behaviour of the earth's crust, both on a large scale and down to the crystal level. When interpreting data, it is therefore important to bear in mind that rocks also have a memory.