Changing direction of magnetic fabric in a thrust unit: an example from the Karkonosze-Izera massif (SW Poland)

The southern and eastern margins of the Karkonosze-Izera massif in the West Sudetes expose a nappe pile overthrust toward the NW onto the pre-Variscan continental basement of the Saxothuringian basin. The uppermost thrust she et, the Leszczyniec nappe, shows an entirely different structural pattern i n comparison to all underlying units. Although this contrast of structural trends has been long recognized, the irregular distribution of structural d ata prevented its reliable tectonic interpretation. Therefore, the AMS meth od was applied in that area to collect more structural information from met a-igneous, often massive and weakly foliated and lineated rocks of the Lesz czyniec unit. An analysis of the magnetic fabric confirms the general diffe rence of structural plan between the Leszczyniec nappe and the underlying t ectonic units, interpreted below to result from the juxtaposition of entire ly decoupled crustal segments. Furthermore, the AMS data reveals a discrepa ncy of the magnetic fabric within the Leszczyniec unit itself, between the metabasites and penetrating them metagranitoids. Thee latter rocks demonstr ate a continuous transition of a structural trend towards that, typical of the underlying nappe pile. This abrupt change probably reflects an uplift o f the Leszczyniec unit into the shallower crustal level dominated by a diff erent deformation regime. (C) 2000 Elsevier Science Ltd. All rights reserve d.