Orogen-transverse tectonic window in the Eastern Himalayan fold belt: A superposed buckling model |
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| Institution: | 1. Department of Geology, University of Calcutta, 35, Ballygunge Circular Road, Kolkata, West Bengal 700019, India;2. Department of Geological Sciences, Jadavpur University, Kolkata 700032, India;1. Univ. Montpellier2, CNRS, UMR5243, Géosciences, CC060 UM2, 34095 Montpellier Cedex 5, France;2. CNRS, UPMC Univ. Paris 06, UMR7619, METIS, 75005 Paris, France;1. DipNeT, Sassari University (Italy), via Piandanna 4, 07100 Sassari, Italy;2. Dipartimento dj Scienze Chimiche e Geologiche, Cagliari University (Italy), via Trentino 51, 09127, Italy;1. Hans Ramberg Tectonic Laboratory, Department of Earth Sciences, Uppsala University, Villavagen 16, SE-752 36 Uppsala, Sweden;2. Steinmann-Institut, University of Bonn, D-53115 Bonn, Germany;1. Laboratorio de Modelado Geológico, Instituto de Estudios Andinos “Don Pablo Groeber” (IDEAN), Departamento de Ciencias Geológicas, FCEN, Universidad de Buenos Aires, BsAs C1428EGA, Argentina;2. School of Ocean and Earth Science and Technology, University of Hawaii, 1680 East-West Rd., Honolulu, HI 96822, USA;3. Schoolof Earth and Space Exploration, Arizona State University, Tempe, AZ, USA;4. Department of Geosciences, University of Massachusetts, Amherst, MA 01002, USA;5. Geodetic Science, Ohio State University, Columbus, OH, USA |
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| Abstract: | The Eastern Lesser Himalayan fold-thrust belt is punctuated by a row of orogen-transverse domal tectonic windows. To evaluate their origin, a variety of thrust-stack models have been proposed, assuming that the crustal shortening occurred dominantly by brittle deformations. However, the Rangit Window (RW) in the Darjeeling-Sikkim Himalaya (DSH) shows unequivocal structural imprints of ductile deformations of multiple episodes. Based on new structural maps, coupled with outcrop-scale field observations, we recognize at least four major episodes of folding in the litho-tectonic units of DSH. The last episode has produced regionally orogen-transverse upright folds (F4), the interference of which with the third-generation (F3) orogen-parallel folds has shaped the large-scale structural patterns in DSH. We propose a new genetic model for the RW, invoking the mechanics of superposed buckling in the mechanically stratified litho-tectonic systems. We substantiate this superposed buckling model with results obtained from analogue experiments. The model explains contrasting F3–F4 interferences in the Lesser Himalayan Sequence (LHS). The lower-order (terrain-scale) folds have undergone superposed buckling in Mode 1, producing large-scale domes and basins, whereas the RW occurs as a relatively higher-order dome nested in the first-order Tista Dome. The Gondwana and the Proterozoic rocks within the RW underwent superposed buckling in Modes 3 and 4, leading to Type 2 fold interferences, as evident from their structural patterns. |
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| Keywords: | Rangit window Ductile deformations Multi-ordered superposed buckling Types 1 and 2 interference patterns Tista dome |
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