Mantle lithosphere transition from the East European Craton to the Variscan Bohemian Massif imaged by shear-wave splitting

L Vecsey,J Plomerová,V Babuška

doi:10.5194/se-5-779-2014

Abstract

Abstract. We analyse splitting of teleseismic shear waves recorded during the PASSEQ passive experiment (2006–2008) focused on the upper mantle structure across and around the Trans-European Suture Zone (TESZ). Altogether 1009 pairs of the delay times of the slow split shear waves and orientations of the polarized fast shear waves exhibit lateral variations across the array, as well as back-azimuth dependences of measurements at individual stations. Variable components of the splitting parameters can be associated with fabrics of the mantle lithosphere of tectonic units. In comparison with a distinct regionalization of the splitting parameters in the Phanerozoic part of Europe that particularly in the Bohemian Massif (BM) correlate with the large-scale tectonics, variations of anisotropic parameters around the TESZ and in the East European Craton (EEC) are smooth and of a transitional character. No general and abrupt change in the splitting parameters (anisotropic structure) can be related to the Teisseyre–Tornquist Zone (TTZ), marking the edge of the Precambrian province on the surface. Instead, regional variations of anisotropic structure were found along the TESZ/TTZ. The coherence of anisotropic signals evaluated beneath the northern part of the Brunovistulian in the eastern rim of the BM and the pattern continuation to the NE towards the TTZ, support the idea of a common origin of the lithosphere micro-plates, most probably related to Baltica. Smooth changes in polarizations of the core-mantle boundary refracted shear waves (SKS), polarizations, or even a large number of null splits northward of the BM and further across the TESZ towards the EEC indicate less coherent fabrics and a transitional character of structural changes in the mantle beneath the surface trace of the TESZ/TTZ. The narrow and near-vertical TTZ in the crust does not seem to have a steep continuation in the mantle lithosphere. The mantle part of the TESZ, whose crust was formed by an assemblage of suspect terranes adjoining the EEC edge from the southwest, appears in our measurements of anisotropy as a relatively broad transitional zone in between the two lithospheric segments of different ages. We suggest a southwestward continuation of the Precambrian mantle lithosphere beneath the TESZ and the adjacent Phanerozoic part of Europe, probably as far as towards the Bohemian Massif.

Highlights

The Trans-European Suture Zone (TESZ) represents a distinct tectonic feature that can be traced through northwestern to southeastern Europe at a length of ∼ 3500 km and manifests the contact zone between the Precambrian and Phanerozoic Europe (Fig. 1)
Though this presentation shows only azimuthal anisotropy with the π-periodicity, we can identify main large upper mantle provinces with different anisotropic signal: the orientations from W–E prevail in the Bohemian Massif (BM) in general, less coherent fast S orientations occur to the northwest of the BM, while between the Moravian Line and the www.solid-earth.net/5/779/2014/
We have analysed splitting of shear waves (SKS phases) recorded during the PASSEQ passive experiment focused on a study of the upper mantle structure across the TransEuropean Suture Zone (TESZ). 1009 pairs of the delay times of the slow split shear waves and orientations of the polarized fast shear waves exhibit lateral variations within the array, even if evaluated from the same event

Summary

Introduction

The Trans-European Suture Zone (TESZ) represents a distinct tectonic feature that can be traced through northwestern to southeastern Europe at a length of ∼ 3500 km and manifests the contact zone between the Precambrian and Phanerozoic Europe (Fig. 1). Spakman, 1991; Babuška et al, 1998; Piromallo and Moreli, 2003; Majorowicz et al, 2003; Artemieva, 2009; Jones et al, 2010; Debayle and Richard, 2012). The region westward of the TESZ represents a Variscan assemblage of micro-plates with varying lithosphere thickness and fabrics, partly rimmed by rifts and subduction zones reflecting micro-plate collisions Plomerová and Babuška, 2010). The central part of the long TESZ, running through the territory of Poland, is a zone of about 150–200 km wide.

Results

Discussion

Conclusion