Symmetry of pebble-deformation involving solution pits and slip-lineations in the northern Alpine Molasse Basin |
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| Institution: | 1. Departamento de Petrología y Geoquímica, UCM, IGEO (UCM-CSIC), Madrid, Spain;2. Instituto Nacional del Carbón, INCAR-CSIC, Oviedo, Spain;3. Departamento de Estratigrafía, UCM, IGEO (UCM-CSIC), Madrid, Spain;4. EOST, Université de Strasbourg, Strasbourg, France;1. Department of Geology, Saint Mary''s University, Halifax, Nova Scotia, B3H 3C3, Canada;2. Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia, B2Y 4A2, Canada;1. Key Laboratory of Orogenic Belt and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, China;2. Institute of Oil & Gas, Peking University, Beijing 100871, China;3. Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China;4. Department of Earth, Atomospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, United States;5. CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;6. College of Geosciences, China University of Petroleum(Beijing), Beijing 102249, China |
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| Abstract: | Deformation features on pebbles of the Alpine Molasse Basin are most clearly developed in carbonate components. Ductile distortion is small; most of the pebbles moved against each other to produce solution pits and slip-lineations on the pebble surfaces. The complete lineation field has a triaxial geometry. From a compressional axis of divergence with maximum solution, fields of diverging lineations extend to meet at a plane of convergence. Their ends bend away from an intermediate axis towards an (extensional) axis of convergence. The strain-symmetry is pure shear for orthogonal lineation-field axes, uniaxial compression and extension representing special cases. The angle α between the divergent and the convergent axes decreases from 90 to 0° with the transition from pure to simple shear. For Molasse pebbles α angles between 90 and 60° were usually observed. Regional compression developed perpendicular to the Alpine structures and parallel to bedding, with increasing deviations near the Alpine border. Zones are recorded of vertical and horizontal extension and of compression perpendicular to bedding and horizontal extension perpendicular to the Rhinegraben existing at the northern border of the Molasse Basin. |
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