Formation, deformation and exhumation of a high-pressure/ultra-high-pressure mélange - the Adula Nappe (Central Alps).

• Applicant: Professor Dr. Thorsten Nagel
• Subject Area: Palaeontology
• Term: from 2009 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 128245454

We want to study the formation and exhumation of an eclogite facies, tectonic melange in the Adula Nappe (Central Alps). Most findings of rocks that were subducted to ultra-high-pressure (UHP) metamorphic conditions (depths in excess of 80 kilometres) are located in melange zones of dominantly continental rocks similar to the Adula Nappe and exhumation of such rocks back to the surt ace represents one of the most discussed tectonic problems. In particular, the relation between melange formation and exhumation along the subducting plate boundary remains controversial. Some studies propose Intense mixing of rocks simultaneous with exhumation during continuous return flow in a weak subduction channel, while others argue for exhumation of coherent HP/UHP units in distinct exhumation events (implying that the melanges formed eariier during subduction. The Adula Nappe represents a perfect example to attack this fundamental problem. We will (1) determine the time of peak pressure conditions in eclogites and garnet-whIte-mica schists throughout the entire Adula Nappe by dating garnets, (2) determine pressuretemperature histories of the same samples, and (3) unravel kinematics and metamorphic conditions of the eariiest deformation postdating peak-pressure conditions. We will identify the nappe internal strain associated with exhumation and find out whether the Adula Nappe was exhumed as a coherent unit or was amalgamated from components with different pressure-temperature-time histories during exhumation. Hence, this study will improve the overall knowledge about the behaviour of continental crust in a subduction channel.

• DFG Programme: Research Grants
• Participating Person: Professor Dr. Nikolaus Froitzheim