A tectonic origin of magnetic fabric in the Shemshak Group from Alborz Mts. (northern Iran) |
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| Institution: | 1. Geological Survey of Iran, Azadi Square, Meraj Avenue, 13185-1494 Tehran, Iran;2. Dipartimento di Scienze, Largo San Leonardo Murialdo 1, 00146 Roma, Università Roma TRE, Rome, Italy;1. Munich, Germany;2. National Iranian Oil Company (NIOC) Exploration Directorate, Tehran, Iran;1. Departamento de Geología, Universidad de Oviedo, C/Jesús Arias de Velasco s/n, 33005 Oviedo, Spain;2. National Iranian Oil Company, Exploration Directorate, Seoul Ave., Tehran, 1994814695, Iran;1. Key Laboratory of Crustal Dynamics, China Earthquake Administration, Beijing 100085, China;2. Institute of Crustal Dynamics, China Earthquake Administration, Beijing 100085, China;3. China University of Geosciences (Beijing), Beijing 100083, China;4. Institute of Geology, China Earthquake Administration, Beijing 100029, China;1. Computational Geology Laboratory, Polish Geological Institute – National Research Institute, Wroc?aw, Poland;2. Physics of Geological Processes, University of Oslo, Norway;3. Department for Geodynamics and Sedimentology, University of Vienna, Austria |
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| Abstract: | The magnetic lineation observed in “undeformed” sedimentary units has been interpreted either as an indication of paleoflow direction, or as a result of tectonic overprint which progressively modifies the original sedimentary fabric related to compactional processes. Distinguishing between the two processes is not always easy. In fact, most studies of the Anistropy of Magnetic Susceptibility (AMS) of “undeformed” sequences have been carried out in fine-grained sediments from foredeep sequences, which are characterized by sedimentary flow directions which are almost parallel to the main deformation structures, like thrust faults and folds. In the Alborz Mts., the Upper Triassic–Lower Jurassic Shemshak Group was deposited in a foreland to molassic basin of the Eo-Cimmerian orogen and now outcrops in several folds which are oriented parallel to the curved chain. Paleoflow directions are generally oblique to the main tectonic structures, being directed SSW to SSE and showing negligible changes in their orientation along the Alborz Mountains. We have, therefore, the opportunity to distinguish between tectonic- or sedimentary-related origins of the magnetic lineation. The AMS results show that magnetic lineations of the Shemshak Group are oriented almost parallel to the main fold axes and thrust structures, which follow the Alborz Mts. curved trend, suggesting that magnetic lineation is of tectonic origin in fine to medium grained, mostly massive sandstones, and confirming that AMS is a valuable tool to study deformation processes in sedimentary rocks. |
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| Keywords: | AMS Magnetic lineation Compressional tectonics Shemshak Group Northern Iran |
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