Intraplate seismicity in the western Bohemian Massif (central Europe): A possible correlation with a paleoplate junction |
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| Institution: | 1. Senckenberg Museum für Naturkunde Görlitz, Am Museum 1, PF 300154, 02826 Görlitz, Saxony, Germany;2. Institute of Geophysics, Academy of Sciences of the Czech Republic, Boční II/1401, 141 31 Praha 4, Czech Republic;1. Institute of Earth Sciences, University of Graz, Heinrichstraße 26, 8010 Graz, Austria;2. School of Earth Sciences, The University of Melbourne, Vic. 3010, Australia;3. Isotope Geosciences Unit, Scottish Universities Environmental Research Centre, Scottish Enterprise Technology Park, East Kilbride G75 0QF, UK;4. Institute of Geology, University of Innsbruck, Innrain 52, 6020 Innsbruck, Austria |
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| Abstract: | Locations of the Eger Rift, Cheb Basin, Quaternary volcanoes, crustal earthquake swarms and exhalation centers of CO2 and 3He of mantle origin correlate with the tectonic fabric of the mantle lithosphere modelled from seismic anisotropy. We suggest that positions of the seismic and volcanic phenomena, as well as of the Cenozoic sedimentary basins, correlate with a “triple junction” of three mantle lithospheres distinguished by different orientations of their tectonic fabric consistent within each unit. The three mantle domains most probably belong to the originally separated microcontinents – the Saxothuringian, Teplá-Barrandian and Moldanubian – assembled during the Variscan orogeny. Cenozoic extension reactivated the junction and locally thinned the crust and mantle lithosphere. The rigid part of the crust, characterized by the presence of earthquake foci, decoupled near the junction from the mantle probably during the Variscan. The boundaries (transitions) of three mantle domains provided open pathways for Quaternary volcanism and the ascent of 3He- and CO2-rich fluids released from the asthenosphere. The deepest earthquakes, interpreted as an upper limit of the brittle–ductile transition in the crust, are shallower above the junction of the mantle blocks (at about 12 km) than above the more stable Saxothuringian mantle lithosphere (at about 20 km), probably due to a higher heat flow and presence of fluids. |
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