An array study of lithospheric structure across the Protogine zone, Varmland, south-central Sweden - signs of a paleocontinental collision

A small seismological array was installed on bath sides of the Protogine Zo ne (PZ) in Varmland, south-central Sweden, to study the structure of the ma ntle lithosphere and lateral variations of its anisotropy. No distinct isot ropic velocity anomalies were detected by tomography in the upper mantle ar ound the PZ, The observed velocity variations depending on the direction of propagation can be explained by anisotropy within the subcrustal lithosphe re on both sides of the suture, The best solution of a joint analysis of an isotropic inferences from teleseismic P-residual spheres and an inversion o f shear-wave splitting parameters, resulted in 3D self-consistent anisotrop ic models of blocks of the subcrustal lithosphere. The anisotropic structur es within the lithosphere an approximated by hexagonal models (k(P) = 5%) w ith low-velocity symmetry axes. The high-velocity planes dip to the E in a region westward of the PZ and to the NW eastward of the PZ. The PZ can be i nterpreted as a steep and narrow suture cutting the whole lithosphere and s eparating the two anisotropic blocks of different origin. (C) 2001 Elsevier Science B.V. All rights reserved.