Reconstruction of early phase deformations by integrated magnetic and mesotectonic data evaluation

• Published in: Tectonophysics 2018-02, Vol.726, p.73-85
• Main Authors: Sipos, András A., Márton, Emő, Fodor, László
• Format: Article
• Language: English
• Subjects: Anisotropy; Brittleness; Cementation; Data; Deformation; Deformation mechanisms; Ductile-brittle transition; Evaluation; Fracture mechanics; Geological faults; Magnetic fabrics; Magnetic permeability; Magnetic susceptibility; Markers; Methods; Orientation; Reconstruction; Reconstruction of weak deformations; Rocks; Rotation; Rotational anisotropy; Sediments; Slip; Statistical tests; Stochastic models; Stochastic stress inversion; Stress; Stresses
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2018.01.019

Markers of brittle faulting are widely used for recovering past deformation phases. Rocks often have oriented magnetic fabrics, which can be interpreted as connected to ductile deformation before cementation of the sediment. This paper reports a novel statistical procedure for simultaneous evaluation of AMS (Anisotropy of Magnetic Susceptibility) and fault-slip data. The new method analyzes the AMS data, without linearization techniques, so that weak AMS lineation and rotational AMS can be assessed that are beyond the scope of classical methods. This idea is extended to the evaluation of fault-slip data. While the traditional assumptions of stress inversion are not rejected, the method recovers the stress field via statistical hypothesis testing. In addition it provides statistical information needed for the combined evaluation of the AMS and the mesotectonic (0.1 to 10 m) data. In the combined evaluation a statistical test is carried out that helps to decide if the AMS lineation and the mesotectonic markers (in case of repeated deformation of the oldest set of markers) were formed in the same or different deformation phases. If this condition is met, the combined evaluation can improve the precision of the reconstruction. When the two data sets do not have a common solution for the direction of the extension, the deformational origin of the AMS is questionable. In this case the orientation of the stress field responsible for the AMS lineation might be different from that which caused the brittle deformation. Although most of the examples demonstrate the reconstruction of weak deformations in sediments, the new method is readily applicable to investigate the ductile-brittle transition of any rock formation as long as AMS and fault-slip data are available. •A new statistical method for nearly rotationally anisotropic AMS data sets•A new stress inversion method based on stochastic considerations•A combined method for simultaneous evaluation of AMS and fault-slip data•A new approach to study the ductile-to-brittle transition of rocks•Field examples from the Pannonian Basin