Low-grade metamorphic units in the Eastern Alps: An important tectonic transition zone

2018 – 2021, Funding: Uni:docs Fellowship programme 2018

Principal Investigator:
Bernhard Grasemann

Benjamin Huet (Geological Survey of Austria, Vienna)
David Schneider (University of Ottawa, Canada)

Sophie Hollinetz

During continent collision and orogeny, the continental crust undergoes deformation and mineral transformations. Between the non-metamorphic upper and high-grade lower crust an intermediate crustal domain experiences mineral transformations and deformation at 300-500°C and <1 GPa (greenschist-facies).
This low-grade metamorphic (LGM) unit comprises and controls major crustal shear zones and links surface and depth processes. However, little research has been done in this field so far, providing ample opportunity to improve the understanding of this zone during orogeny.
In this multidisciplinary project, I will acquire and integrate pressure-temperature-time-deformation (P-T-t-D) data to develop a thermo-mechanical evolution model for LGM units of orogens, using the Eastern Alps as natural laboratory.

A large share of the exposed crust in the Eastern Alps consists of LGM units in tectonic key positions at top and bottom of the Eo-Alpine extrusion wedge. Understanding the processes occurring there has a major impact on our comprehension of the evolution of the whole orogen, however, no modern P-T-t-D data is known for this part so far.

This project aims
to compensate this deficit of data by combining state-of-the-art methods in metamorphic petrology, structural geology and geochronology.
Structural data and samples are collected in several representative areas selected based on preparational work on existing samples provided by the Geological Survey of Austria.
Metamorphic conditions are determined by combining petrographic and chemical characterization using scanning electron microscopy and electron microprobe analysis with thermodynamic forward modeling.
The age of metamorphism and deformation is determined by high-precision U-Th-Pb dating of accessory minerals using laser-ablation inductively-coupled-plasma mass spectroscopy (LA-ICP-MS).

Finally, the acquired data will be integrated in a time- and space-resolved thermo-mechanical model that predicts cooling and exhumation rates and the viscosity of this part of the crust.
This model will be compared to models developed in other mountain belts to infer general trends for orogenic processes on Earth.