Transversely isotropic lower crust of Variscan central Europe imaged by ambient noise tomography of the Bohemian Massif
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Published:2021-05-11
Issue:5
Volume:12
Page:1051-1074
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ISSN:1869-9529
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Container-title:Solid Earth
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language:en
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Short-container-title:Solid Earth
Author:
Kvapil Jiří, Plomerová Jaroslava, Kampfová Exnerová HanaORCID, Babuška Vladislav, Hetényi GyörgyORCID,
Abstract
Abstract. The recent development of ambient noise tomography, in
combination with the increasing number of permanent seismic stations and
dense networks of temporary stations operated during passive seismic
experiments, provides a unique opportunity to build the first
high-resolution 3-D shear wave velocity (vS) model of the entire
crust of the Bohemian Massif (BM). This paper provides a regional-scale
model of velocity distribution in the BM crust. The velocity model with a
cell size of 22 km is built using a conventional two-step inversion approach from
Rayleigh wave group velocity dispersion curves measured at more than 400
stations. The shear velocities within the upper crust of the BM are
∼0.2 km s−1 higher than those in its surroundings. The
highest crustal velocities appear in its southern part, the Moldanubian
unit. The Cadomian part of the region has a thinner crust, whereas the crust
assembled, or tectonically transformed in the Variscan period, is thicker.
The sharp Moho discontinuity preserves traces of its dynamic development
expressed in remnants of Variscan subductions imprinted in bands of crustal
thickening. A significant feature of the presented model is the
velocity-drop interface (VDI) modelled in the lower part of the crust. We
explain this feature by the anisotropic fabric of the lower crust, which is
characterised as vertical transverse isotropy with the low velocity being
the symmetry axis. The VDI is often interrupted around the boundaries of the
crustal units, usually above locally increased velocities in the lowermost
crust. Due to the north-west–south-east shortening of the crust and the late-Variscan
strike-slip movements along the north-east–south-west oriented sutures preserved in
the BM lithosphere, the anisotropic fabric of the lower crust was partly or
fully erased along the boundaries of original microplates. These weakened
zones accompanied by a velocity increase above the Moho (which indicate an
emplacement of mantle rocks into the lower crust) can represent channels
through which portions of subducted and later molten rocks have percolated
upwards providing magma to subsequently form granitoid plutons.
Publisher
Copernicus GmbH
Subject
Paleontology,Stratigraphy,Earth-Surface Processes,Geochemistry and Petrology,Geology,Geophysics,Soil Science
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