An integrated magnetic susceptibility anisotropy (AMS) and structural geological study on Cenozoic clay-rich sediments from the Transdanubian Range

摘要

Systematic structural and anisotropy of magnetic susceptibility (AMS) measurements were carried out on Cenozoic clay-rich deposits from the Transdanubian Range, central part of the Alcapa Unit. The aim was to improve the knowledge of the Neogene tectonic evolution of the area and of the connection of the stress field and the magnetic fabric of the sediments. The measurements of AMS revealed dominant foliation with weak lineation for Middle Eocene-Lower Miocene sediments. The directions of AMS lineation are aligned either with the direction of NNE-SSW extension of a strike slip phase (30-19 Ma) or with the direction of NE-SW extension of the main rifting phase of the Pannonian Basin (19-14 Ma).The studied Late Miocene sediments have foliated AMS fabric, maximum and intermediate AMS directions are intermixed, and the AMS fabrics do not show any sign of tectonic deformation. In contrast, joints and faults were observed in the same rocks. Detailed structural analysis shows two extensional phases between ca. 10-4 Ma, with E-W to WNW-ESE and with NW-SE extension, respectively, and the youngest neotectonic strike-slip phase. The contrast between the presence of markers of brittle deformation and the absence of tectonically-induced AMS lineation is striking, since the same types of sediments in the South Pannonian basin show just the opposite. The explanation may be that northward-moving and CCW-rotating Adria caused strong compression in the southern Pannonian Basin, resulting in ductile deformation of the clay-rich sediments and systematic reorganization of AMS texture, while in our study area sediments of similar character and age were at a larger distance from the strongly deforming basin part.