Tectonics of the Leinetal Graben: unsolved questions

The Leinetal Graben (LTG) is a key element of Germany´s post-Variscan fault network. It is part of the generally NNE-trending fault system running from the Upper Rhine Graben to the eastern border of the Lower Saxony Basin (LSB) and connects NW-SE-striking faults of the LSB with at least one regional fault in the Thuringian Syncline over a distance of some 50 km. This geometry suggests displacement transfer along the LTG. The link to the inverted LSB predicts two main phases of motion on the LTG faults: sinistral transtension during LSB opening (Triassic to Early Cretaceous) and dextral transpression during inversion (Late Cretaceous). Paleostress analysis (Sippel et al. 2008) does not contradict this model but has sparse observations from the LTG. The complicated western border of the LTG may record more strike-slip deformation while the eastern border is dominated by normal faulting. The role of Zechstein salt in the evolution of the LTG is unclear. Evacuation of thick, stratiform salt or collapse of a Triassic salt wall (Tanner et al. 2015) have been proposed, with minimal involvement of the basement. Concentrated brines drilled at about 400 m depth have been interpreted as revealing salt-intruded normal faults. The LTG is typically shown as part of the European Cenozoic Rift System, but may have remained inactive in Cenozoic time. Oligo-Miocene sediments and basalts are only present on the western shoulder but not within the LTG. The present topography of the graben may reflect river incision into soft Keuper and Lower Jurassic strata.