Tectonometamorphism in the hanging wall of extruding rocks

A large number of tectonic models try to explain exhumation processes of continental high-pressure metamorphic rocks. Even for coevally exhumed eclogite-bearing Austroalpine basement Units of the Eastern Alps (Thöni, 1999), very different exhumation models have been proposed. Detailed and correlated petrological, structural and geochronological data therefore are required in order to impose constraints on tectonic models applicable to exhuming HP rocks. The proposed study focuses on the hanging wall units (= Ötztal-Stubai basement) of the eclogite-bearing Texel Complex, which experienced subduction-related burial to c. 45 km depth. An extrusion model has been proposed for the exhumation of the Texel Complex from eclogite to greenschist facies metamorphic conditions (Sölva et al., 2005). The major aspects of the proposed project concern: 1) quantification of the metamorphic conditions in the hanging wall during extrusion in the footwall: i) estimation of maximum burial depths of the hanging wall rocks during the high-pressure event, ii) constraints on the regional distribution of metamorphic P and T in profiles parallel to the extrusion direction, in order to iii) test the significance of conductive heating by the exhuming footwall compared to tectonic heat advection-processes as a cause for Cretaceous metamorphism in the hanging wall; 2) investigation of the structural imprint of the hanging wall related with extrusion of the footwall: i) correlation of deformation and crystallization processes during Cretaceous metamorphism, ii) constraints on the extent and the kinematics of extrusion-related deformation in the hanging wall units, iii) investigation of the deformational imprint pre- and post-dating the extrusion process; 3) age constraints on deformation and cooling by Rb-Sr and fission track dating; 4) comparison of the data with current tectonic models applied to intracontinental subduction/extrusion systems. The objectives require the application of an interdisciplinary approach. Based on field work, structurally and mineral compositionally well defined spot samples will be used for geothermobarometry, respectively thermodynamic modeling of phase equilibria, as well as for geochronology. The results will yield new insights on the P-T-t-d evolution and the thermal structure of the hanging wall during extrusion of high-pressure rocks, test a potentially poly-phase versus a single phase exhumation process, extend the extrusion model (Sölva et al., 2005) to the low-temperature cooling history, and finally provide a basis for resolving the pre-Alpine tectonometamorphic evolution of the Austroalpine Ötztal-Stubai basement.