Electrical conductivity structure of the crust and upper mantle beneath the Rhenish Massif.

Abstract

A magnetotelluric survey was undertaken in the Rhenish massif and adjacent areas. Observations were made in the period range 5-3000 s at >70 sites along four profiles. The profiles Eifel-Palatinate, Sauerland-Taunus, and Munsterland-Spessart run normal to the main trend of the Variscan fold belt. The profile Eifel-Rothaargebirge follows the Variscan trend. Results from a 1-D inversion of observed rotationally invariant resistivity and phase values show mainly a southward-dipping intra-crustal conductor, in striking correspondence with a subfluence model or with large-scale overthrusting as geodynamic models of the Rhenish massif. Preliminary 2-D modelling indicates that there is no major dislocation of this conductor at the southern margin of the massif (Hunsruck-Sudrand-Storung). In some areas - especially outside the massif proper - an additional increase of conductivity at shallower depths was found. According to the present stage of data analysis and interpretation, there are no distinct regional differences at upper mantle depth within the massif.-J.M.H.