Preprints
https://doi.org/10.5194/se-2020-176
https://doi.org/10.5194/se-2020-176

  27 Oct 2020

27 Oct 2020

Review status: a revised version of this preprint is currently under review for the journal SE.

Transversely Isotropic Lower Crust of Variscan Central Europe imaged by Ambient Noise Tomography of the Bohemian Massif

Jiří Kvapil1, Jaroslava Plomerová1, Hana Kampfová Exnerová1, Vladislav Babuška1, György Hetényi2, and the AlpArray Working Group Jiří Kvapil et al.
  • 1Institute of Geophysics, Czech Academy of Sciences, Boĉní II/1401, 141 31 Prague 4, Czech Republic
  • 2Institute of Earth Sciences, University of Lausanne, Lausanne, Switzerland
  • For further information regarding the team, please visit the link which appears at the end of the paper.

Abstract. Recent development of ambient noise tomography, in combination with 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 crust of the Bohemian Massif (BM). The velocity model with a cell size of 22 km is built by 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 model provides compelling evidence for a regional-scale of velocity distribution. The Cadomian part of the region has a thinner crust, while 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 thickenings. 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 anisotropic fabric of the lower crust, which is characterized 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 NW SE shortening of the crust and the late Variscan strike slip movements along the NE SW 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 extrusion 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.

Jiří Kvapil et al.

 
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
[Login for authors/topical editors] [Subscribe to comment alert] Printer-friendly Version - Printer-friendly version Supplement - Supplement

Jiří Kvapil et al.

Jiří Kvapil et al.

Viewed

Total article views: 460 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
368 86 6 460 35 2 2
  • HTML: 368
  • PDF: 86
  • XML: 6
  • Total: 460
  • Supplement: 35
  • BibTeX: 2
  • EndNote: 2
Views and downloads (calculated since 27 Oct 2020)
Cumulative views and downloads (calculated since 27 Oct 2020)

Viewed (geographical distribution)

Total article views: 406 (including HTML, PDF, and XML) Thereof 404 with geography defined and 2 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 28 Feb 2021
Download
Short summary
The high-resolution 3-D shear velocity model of the BM crust imaged from high-density data and enhanced depth sensitivity of tomographic inversion. The dominant features of the model are relatively higher vS in the upper crust than in its surrounding, distinct intra crustal interface and a velocity decrease in the lower part of the crust. The low vS in the lower part of the crust is explained by an anisotropic fabric of the lower crust.