Deformation and seismic anisotropy of the lithospheric mantle in the southeastern Carpathians inferred from the study of mantle xenoliths |
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| Authors: | Gyrgy Falus Andrea Tommasi Jannick Ingrin Csaba Szab |
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| Institution: | aEötvös Lorand Geophysical Institute of Hungary, Columbus u. 17-23, H-1145 Budapest, Hungary;bGéosciences Montpellier, CNRS & Université Montpellier 2, F-34095 Montpellier cedex5, France;cMinéralogie, LMTG, University of Paul Sabatier, 14 Av. Edouard Belin, 31000 Toulouse, France;dEötvös University, Budapest, Lithosphere Fluid Research Lab, Pázmány Péter s. 1/c, H-1117 Budapest, Hungary |
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| Abstract: | Peridotite xenoliths with a broad range of textures provides evidence for consistent microstructural evolution in a vertical transect of the shallow lithospheric mantle (35–55 km depth) beneath the Persani Mountains, SE Carpathians, Romania, due to ongoing plate convergence in the Carpathian Arc nearby. The recrystallized grain size, crystal preferred orientations strength, and resulting seismic anisotropy vary continuously and display a strong correlation to equilibrium temperatures, suggesting a continuous change in deformation conditions with depth. The shallowmost xenoliths have microstructures typical of high stress deformation, marked by strong recrystallization to fine grain sizes, which results in weak crystal preferred orientations and anisotropy. The deepest xenoliths have coarse-grained porphyroclastic microstructures and strong crystal preferred orientations. Replacive orthopyroxene structures, consuming olivine, and high H2O concentrations in the pyroxenes are observed in some xenoliths indicating limited percolation of fluids or volatile-rich melts. Despite the high stress deformation and high H2O contents in some of the studied xenoliths, analysis of olivine crystallographic orientations indicates that 100] slip systems, rather than “wet” 001] accommodate most of the deformation in all samples. Seismic anisotropy estimated from the measured olivine and pyroxene crystal preferred orientations suggests that the strike-parallel fast SKS polarization directions and ~ 1 s delay times measured in the SE Carpathians are likely the consequence of convergence-driven belt-parallel flow in the lithospheric mantle. |
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| Keywords: | SE Carpathians mantle xenoliths olivine deformation crystal preferred orientations anisotropy plate convergence subduction collision microstructures recrystallisation |
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