SUBSIDENCE AND TECTONICS OF THE SAAR-NAHE BASIN (SOUTHWESTERN GERMANY)

The Saar-Nahe-Basin in SW-Germany is one of the largest Permo-Carbonif erous basins in the internal zone of the Variscides. Its evolution is closely related to movements along the Hunsruck Boundary Fault, which separates the Rhenohercynian and the Saxothuringian zones. Recent deep seismic surveys indicate that the Saar-Nahe-Basin formed in the hangi ng wall of a major detachment which soles out at lower crustal levels at about 16 km depth. Oblique extension along an inverted Variscan thr ust resulted in the formation of a half-graben, within more than 8 km of entirely continental strata accumulated. The structural style withi n the basin is characterized by normal faults parallel to the basin ax is and orthogonal transfer fault zones. Balanced cross-section constru ction and subsidence analysis indicate extension of the orogenically t hickened lithosphere by 35%. Subsidence modeling shows discontinuous d epth-dependent extension with laterally varying extension factors for crust and mantle lithosphere. Thus, the offset between maximum rift an d thermal subsidence can be explained by a zone of mantle extension sh ifted laterally with respect to the zone of maximum crustal extension.