Publications

The main structures of the mid-European lithosphere, crossing Europe from the Iberian peninsula to the Bohemian Massif, are predominantly formed by the Variscan orogeny. To investigate the anisotropy of the mantle at the transition zone between the two Variscan units, the Saxothuringicum and the Moldanubicum, we carried out a field experiment in SE Germany in 1995-1996: 23 mobile broad-band stations were installed for 6 months in the Vogtland-Oberpfalz-Bavarian Forest area. The station profile crossed the suture zone of the Saxothuringicum and Moldanubicum near the KTB borehole (German Continental Deep Drilling Program). With a mean station spacing of about 10 km? we intended to obtain a high lateral resolution of the anisotropy parameters and to resolve possible changes when passing the suture zone. The analysis of the observed birefringence of SKS phases shows E-W directions for the fast polarization. Therefore, the directions deviate only slightly from the strike of the Hercynian mountain belt and from the direction of the absolute plate motion in that region. Indications for the transition zone come from a rotation of the fast polarization direction from 86 degrees +/- 13 degrees in the northern part of the profile (Saxothuringicum) to 110 degrees +/- 15 degrees in the southern part (Moldanubicum) as well as from strong variations of the splitting parameters with respect to the azimuths of the incoming waves in the middle of the profile. We interpret these variations as an expression of a complex mantle structure formed either by several anisotropic layers with inclined symmetry axes in at least one layer or by a model consisting of inhomogeneous anisotropic layers. A comparison of the azimuthal variations of the splitting parameters in the middle of the profile with those observed at the Grafenberg station GRAl-situated in the central part of the transition zone approximately 100 km to the west-shows remarkable differences, which may reflect lateral variations in the direction and inclination of the symmetry axes in the transition zone even on a small scale. Both observations-the change in the fast polarization direction from the northern to the southern part as well as the variations with respect to different azimuths in the middle of the profile-suggest that the transition zone between the Saxothuringicum and the Moldanubicum continues down into the upper mantle.

---

Plenefisch, T.; Klinge, K.; Kind, R. (2001): Upper mantle anisotropy at the transition zone of the Saxothuringicum and Moldanubicum in southeast Germany revealed by shear wave splitting. Geophysical Journal International, 144, 2, 309-319.