Parametric unfolding of flexural folds using palaeomagnetic vectors
Maria José Ramón, Emilio L. Pueyo, Guillaume Caumon, José Luis Briz, 2016. "Parametric unfolding of flexural folds using palaeomagnetic vectors", Palaeomagnetism in Fold and Thrust Belts: New Perspectives, E. L. Pueyo, F. Cifelli, A. J. Sussman, B. Oliva-Urcia
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Providing that a primary and reliable record of the magnetic field and its reference in a deformed area exists, the incorporation of palaeomagnetic constraints in restoration methods reduces uncertainty of rotation because such constraints can be applied both before and after deformation. In this paper, we utilize palaeomagnetic data to improve an unfolding algorithm based on the parameterization of the surface using isometric constraints. This method is more robust than others based on piecewise restoration of a triangulated surface, which are dependent on the meshing and, especially, on the pin-element. A disadvantage of this approach is that parametric restoration is sensitive to the initial solution, which hampers results for complex non-coaxial or non-cylindrical structures. We show that the use of palaeomagnetism as the initial gradient of one of the parameters improves the results of the method. We use analogue models to test the method because the expected restoration result can be stated, since the initial surface is known. We study the restoration sensitivity to surface meshing and the initial palaeomagnetic orientation. All in all, the use of palaeomagnetic vectors in the studied analogue models achieves the best restoration results. The implementation of palaeomagnetic vectors is crucial to obtain reliable 3D restorations of complex structures.
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Palaeomagnetism is a technique used to understand complex deformation patterns in fold-and-thrust belts; it can be used to characterize the distribution, magnitude and timing of vertical axis rotations, an elusive variable using other methods. A combination of palaeomagnetic and structural geology analyses has helped to unravel the geometry and kinematics of fold-and-thrust belts around the world and of different geological ages for more than 50 years. This volume comprises three sections: the first shows thorough overviews of western Mediterranean arcs and the western Carpathians; the second depicts several examples from the Andes, the Alps, Anatolia, Pyrenees, Iberian Ranges and the Atlas; and the third shows the latest research on the use of palaeomagnetism to understand fold-and-thrust belts in 3D and 4D in a more quantitative way and it also includes some methodological proposals to avoid common errors. In the papers of the first two sections, the combination of palaeomagnetic analyses with structural data, AMS or magnetostratigraphic analyses demonstrate the usefulness of palaeomagnetism in deciphering complex deformation patterns in fold-and-thrust belts.