Miocene rotations in the Eastern Alps — palaeomagnetic results from intramontane basin sediments

Abstract

A palaeomagnetic study of late Early Miocene to late Middle Miocene sediments from the Eastern Alpine intramontane basins revealed counterclockwise rotations in the Ennstal, in the western part of the Noric and in the Lavanttal depressions. For the basal strata of the basins, declinations are between 273° and 315°, while for the younger strata they are between 321° and 333°, in perfect agreement with observations from the Klagenfurt basin. The results suggest synsedimentary rotation during the lateral tectonic extrusion of the Eastern Alps (ca. 17–13 Ma), which was also responsible for the formation of the mostly transtensional basins. We propose a model in which domino-shaped blocks, separated by NNW–SSE trending dextral faults, rotated counterclockwise due to faster eastward motion in the south relative to areas further north. The protrusion of the Bohemian spur inhibited eastward motion in the northern part of the study area, thus creating a sinistral wrench corridor. After lateral extrusion had ceased the counterclockwise rotation continued probably as ‘en bloc’ rotation of ca. 30°. Clockwise rotation was observed in the eastern part of the Noric depression, which appears to belong to a limited area with complex rotation pattern near the eastern margin of the Alps. This area is wedged between the counterclockwise rotated Eastern Alps and the similarly rotated North Pannonian area in Hungary.