Magnetic fabric, shape preferred orientation and regional strain in granitic rocks

Some remarks on fabric overprints and constrictional AMS fabrics in igneous rocks

“…Hrouda was the first to recognize complex trajectories of magnetic fabric symmetries and intensities related to the process of deformation overprint. In magmatic rocks, deformation overprints of various origins are recognized by several authors dealing with structural studies in the field (e.g., Ž ák et al 2005Sen and Mamtani 2006). However, the magnetic fabric method provides only a record of the bulk strain, and therefore, the maps of the anisotropy of magnetic susceptibility ellipsoid shapes and anisotropy degree may provide confusing information as shown for instance by Kratinová et al (2010).…”

Evaluation of a regional strain gradient in mylonitic quartzites from the footwall of the Main Central Thrust Zone (Garhwal Himalaya, India): Inferences from finite strain and AMS analyses

“…A positive correlation between magnitude of strain and P 0 has been demonstrated in experimentally deformed sandstone (Borradaile and Alford, 1987). In naturally deformed rocks, P 0 has been efficiently used as a strain-intensity gauge (Borradaile and Mothershill, 1984;Archanjo et al, 1995;Henry et al, 2004;Mukherji et al, 2004;Sen et al, 2005;Sen and Mamtani, 2006). In the context of the present tectonic setting of the MCT, the results of Borradaile and Mothershill (1984) and Sen et al (2005) are particularly interesting.…”

“…The measurement of anisotropy of magnetic susceptibility (AMS) is one such technique that has been recently used to gauge strain in rocks that are devoid of strain markers (e.g. Hrouda, 1993;Tarling and Hrouda, 1993;Archanjo et al, 1995;Borradaile and Henry, 1997;Mukherji et al, 2004;Sen et al, 2005;Sen and Mamtani, 2006).…”

Modelling complex geological circular data with the projected normal distribution and mixtures of von Mises distributions

“…Witts et al (2012) used a similar procedure to identify trends in palaeocurrent data from the dip and dip azimuth of sand bars in a Cenozoic sedimentary succession in Indonesia. Sen and Mamtani (2006) used the κ parameter of the von Mises distribution to characterise the preferential orientation of biotite in thin sections of granite which was related to variations in regional strain. O'Brien et al (2012) used von Mises distributions to characterise the orientations of fault plane solutions -with confidence intervals -before, during and after seismic swarms.…”