Subduction-driven shortening and differential exhumation in a Cadomian accretionary wedge: The Teplá–Barrandian unit,Bohemian Massif |
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| Authors: | Jaroslava Hajná Ji?í ?ák Václav Kachlík Martin Chadima |
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| Institution: | 1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;2. School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;3. Department of Geology, Hanoi University of Mining and Geology, Hanoi, Viet Nam;4. John de Laeter Centre, Curtin University, Perth, WA 6102, Australia;5. General Department of Geology and Minerals of Viet Nam, Hanoi, Viet Nam;1. Institute of Petrology and Structural Geology, Faculty of Science, Charles University, Albertov 6, 12843 Prague, Czech Republic;2. Institute of Geology and Paleontology, Faculty of Science, Charles University, Albertov 6, 12843 Prague, Czech Republic;1. Institute of Geophysics ASCR, v.v.i., Bo?ní II 1401/1a, Prague 4 14131, Czech Republic;2. Center for Lithospheric Research, Czech Geological Survey, Klárov 3, Prague 1 11821, Czech Republic;3. Université de Strasbourg, CNRS, Institut de Physique du Globe de Strasbourg, UMR 7516, 67084 Strasbourg, France;4. Institute of Petrology and Structural Geology, Faculty of Science, Charles University, Albertov 6, Prague 2 12843, Czech Republic;5. Department of Earth Science, University of California, Santa Barbara, California, USA;6. Department of Earth and Planetary Sciences, Johns Hopkins University, MD, USA;1. Centre for Lithospheric Research, Czech Geological Survey, Prague, Czech Republic;2. Ecole et Observatoire des Sciences de la Terre, Université de Strasbourg, France;3. Institute of Petrology and Structural Geology, Charles University in Prague, Czech Republic;4. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, China;5. Institute of Geological Sciences, Polish Academy of Sciences, Krakow, Poland;6. Department of Earth Science, University of California, Santa Barbara, CA 93106, USA;1. Institute of Petrology and Structural Geology, Charles University, Albertov 6, Prague 12843, Czech Republic;2. Boise State University, 1910 University Drive, Boise, USA |
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| Abstract: | The Teplá–Barrandian unit (TBU) of Central Europe's Bohemian Massif exposes perhaps the best preserved fragment of an accretionary wedge in the Avalonian–Cadomian belt, which developed along the northern active margin of Gondwana during Late Neoproterozoic. In the central TBU, three NE–SW-trending lithotectonic units (Domains 1–3) separated by antithetic brittle faults differ in lithology, style and intensity of deformation, magnetic fabric (AMS), and degree of Cadomian regional metamorphism. The flysch-like Domain 1 to the NW is the most outboard (trenchward) unit which has never been significantly buried and experienced only weak deformation and folding. The central, mélange-like Domain 2 is characterized by heterogenous intense deformation developed under lower greenschist facies conditions, and was thrust NW over Domain 1 along a SE-dipping fault. To the SE, the most inboard (arcward) Domain 3 is lithologically monotonous (dominated by graywackes and slates), was buried to depths corresponding up to the lower greenschist facies conditions, where it was overprinted by a pervasive SE-dipping cleavage and then was exhumed along a major NW-dipping normal fault.We interpret these domains to represent allochtonous tectonic slices that were differentially buried and then exhumed from various depths within the accretionary wedge during Cadomian subduction. The NW-directed thrusting of Domain 2 over Domain 1 may have been caused by accretion at the wedge front, whereas the SE-dipping cleavage and SE-side-up exhumation of Domain 3 may record inclined pervasive shortening during tectonic underplating and subsequent horizontal extension of the rear of the wedge. The boundary faults were later reactivated during Cambro–Ordovician extension and Variscan compression.Compared to related terranes of the Cadomian belt, the TBU lacks exposed continental basement, evidence for regional strike-slip shearing, and extensive backarc magmatism and LP–HT metamorphism, which could be interpreted to reflect flat-slab Cadomian subduction. This, in turn, suggests that Cadomian accretionary wedges developed in a manner identical to those of modern settings, elevating the TBU to a key position for understanding the style, kinematics, and timing of accretionary processes along the Avalonian–Cadomian belt. |
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