S₁-cleavage fans in the Moselmulde of the Rheinische Schiefergebirge (Federal Republic of Germany) may be due to a D₃-tectonic event: open folding and reverse faulting

A major problem in the Moselmulde is to explain the change in orientation of both S₁ and S₂ cleavages in distinct regional zones. Existing models used to explain this are not consistent with established field data. Penetrative S₁-fabrics gradually change attitude in sections perpendicular to their regional SW-NE strike. Involute constructions on S₁ reveal an open fold structure that could explain the gradually changing attitude. Misfits in the fold profile coincide with sites where narrow S₁-cleavage fans have been traces for over 50 km along strike in the field. S₃-fabrics, discovered at two sites along one of the three regional S₁-cleavage fans, suggest that the fans are partly due to penetrative microfolding, microshearing and pressure solution. It is suggested here that the large scale structure of the Moselmulde is essentially due to a deformational event, D₃, which caused apparent narrow cleavage fans along moderately NW-dipping reverse faults. The gradual change in attitude of the bedding, S₁- and S₂-cleavage in the zones separated by the regional fans is due to open folding associated with the reverse fault motion. The faults may be generated from a sole thrust which is reconstructed in my profiles at 10 to 15 km depth.