HR: 14:55h
AN: GP12A-06 INVITED     [PDF]
TI: Contrasting Magnetic Fabrics in Sediments of Alpine and Variscan Accretionary Wedges of Central Europe
AU: * Hrouda, F
EM: fhrouda@agico.cz
AF: AGICO Inc., Jecna 29a, Brno, CZ-621 00 Czech Republic
AB: The magnetic fabrics in sediments of the Alpine thrust sheets of the Flysch and Klippen Belts of the West Carpathians range from essentially sedimentary to mostly deformational in origin. The former magnetic fabrics are characterized by virtual parallelism of the magnetic foliations to the bedding and by close relationship of magnetic lineations to the current directions, if observable. These magnetic fabrics are typical of the thrust sheets at both margins of the Flysch Belt. The sheets were probably detached from the wedge relatively early and underwent deformations as rigid bodies (translation and perhaps rotation) without being affected by detectable ductile deformation. The latter magnetic fabrics show significant deflections of the magnetic lineations from the current directions and important deflections of magnetic foliations from the bedding evolving into girdle pattern in magnetic foliation poles. These magnetic fabrics are typical of the central thrust sheets where the magnetic fabric was relatively strongly affected by ductile deformation represented by a combination of simple shear (responsible for overthrust movements) and lateral shortening (mostly bedding-parallel), probably associated with creation and motion of the thrust sheets driven by a push from the rear side. However, the deformation was too weak to give rise to the cleavage. The Variscan thrust sheets of the Rheno-Hercynian Zone of the E Bohemian Massif show very variable magnetic fabrics and deformation fabric elements. In some areas, the achimetamorphism, ductile deformation and degree of AMS are in general weak; the magnetic fabric is oblate, the magnetic foliation is either parallel to the bedding or tends to create a partial girdle in its poles. The strata create buckle folds of long wavelength whose magnetic fabric can be unfolded geometrically. In the other areas, spaced cleavage and relatively tight buckle folds can be found. Magnetic foliation is still mostly parallel to the bedding, but the magnetic lineation is re-oriented into parallelism to the cleavage/bedding intersection lines. The magnetic fabric of the most folds can be unfolded only partially. In the other areas, cleavage folds and very well developed slaty cleavage occur. The degree of AMS is high, the magnetic foliation is parallel to the slaty cleavage and the magnetic lineation is parallel to the cleavage/bedding intersection lines. The magnetic fabric in the folds is homogeneous, the folds cannot be unfolded at all. In places, the slaty cleavage is transposed into the metamorphic schistosity. The magnetic fabric in crystalline rocks neighboring this wedge shows the same orientations as that of the wedge. This is interpreted as underplating the wedge by the detached crystalline basement.
DE: 1518 Magnetic fabrics and anisotropy
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting