HR: 16:50h
AN: GP34A-03    [Abstracts]
TI: Constraints on the Mechanics of Folding from Paleomagnetic Data
AU: * Waldhoer, M
EM: martin.waldhoer@uni-tuebingen.de
AU: Appel, E
EM: erwin.appel@uni-tuebingen.de
AF: University of Tuebingen, Inst. for Geoscience, Sigwartstr. 10, Tuebingen, 72072, Germany
AB: We analyzed published paleomagnetic data sets from fold belts upon actual fold geometry and the way how layers become tilted and rotated during deformation by folding. The analysis bases on the combination of remanence vectors and bedding poles to bipod-like pairs of vectors. These vector pairs have new geometrical properties that allow to study the path of tilting and rotation. From our analysis of more than 100 data sets, several general observations turn out: (1) Bedding strikes at the early stage of folding have a significant variation around a mean strike, with a standard deviation of about 30° on average. A concentric fold geometry as often presupposed in paleomagnetism is rather the exception than the rule. (2) The strike variations originate initially with folding, being a general feature of heterogeneity in the early stage of deformation. Until a layer dip of about 30°-50°, the layers are being tilted around (sub)horizontal axes parallel to respective bedding strike. These findings become evident from the distribution of the intersections of the remanence small circles. (3) When folding proceeds, layers with the dip azimuth parallel to the shortening direction (‘compatible layers') continue in the same way, i.e. the axes of tiling do not change orientation. ‘Incompatible' layers, with the dip azimuth not parallel to the shortening direction, however, become accomodated by rotation around (sub)vertical axes. Tilting and vertical-axis rotation perform simultaneously; the bedding poles follow curved paths in the stereoplot. This process of accomodation is referred to as ‘layer parallelisation‘. It can be observed in paleomagnetic data of strongly folded sediments in various fold belts.
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 1527 Paleomagnetism applied to geologic processes
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly