Suchergebnisse

Mantle xenoliths from the Styrian Basin Volcanic Field (Western Pannonian Basin, Austria) are mostly coarse granular amphibole-bearing spinel lherzolites with microstructures attesting for extensive annealing. Olivine and pyroxene CPO (crystal-preferred orientation) preserve nevertheless the record of coeval deformation during a preannealing tectonic event. Olivine shows transitional CPO symmetry from [010]-fiber to orthogonal type. In most samples with [010]-fiber olivine CPO symmetry, the [001] axes of the pyroxenes are also dispersed in the foliation plane. This CPO patterns are consistent with lithospheric deformation accommodated by dislocation creep in a transpressional tectonic regime. The lithospheric mantle deformed most probably during the transpressional phase after the Penninic slab breakoff in the Eastern Alps. The calculated seismic properties of the xenoliths indicate that a significant portion of shear wave splitting delay times in the Styrian Basin (0.5 s out of approximately 1.3 s) may originate in a highly annealed subcontinental lithospheric mantle. Hydroxyl content in olivine is correlated to the degree of annealing, with higher concentrations in the more annealed textures. Based on the correlation between microstructures and hydroxyl content in olivine, we propose that annealing was triggered by percolation of hydrous fluids/melts in the shallow subcontinental lithospheric mantle. A possible source of these fluids/melts is the dehydration of the subducted Penninic slab beneath the Styrian Basin. The studied xenoliths did not record the latest large-scale geodynamic events in the regionthe Miocene extension then tectonic inversion of the Pannonian Basin. ; We acknowledge the constructive criticism and helpful comments of Q‐K. Xia, an anonymous reviewer, and the Editor, John Geissman. We are grateful to F. Barou for his assistance during EBSD‐SEM analyses. L. E. Aradi is grateful to Bernardo Cesare, Levente Patkó, and Raúl Carampin for their help during the EPMA measurements. The FTIR analyses were carried out with the help of Judith Mihály and Csaba Németh. This research was partially granted by the Hungarian Science Foundation (OTKA, 78425 to Cs. Szabó). K. H.'s work was funded by the European Union Seventh Framework Programme Marie Curie postdoctoral fellowship (grant PIEFGA‐2012‐327226) and by the Juan de la Cierva Postdoctoral Fellowship (grant FPDI‐2013‐16253) of the Spanish Ministry of Economic and Competitiveness (MINECO). This project has been implemented with the support provided to I. J. Kovács from the National Research, Development and Innovation Fund of Hungary, financed under the K119740 funding scheme. The data used in this paper are listed in the references, tables, and supporting information. The raw EBSD and geochemical data are available from the corresponding author upon request. The FTIR spectra are available at the PULI (Pannonian Uniform Lithospheric Infrared spectral database) website (http://puli.mfgi.hu/). This is the 86 publication of the Lithosphere Fluid Research Lab (LRG).