Degree of magnetic anisotropy as a strain intensity gauge in ferromagnetic granites

Abstract

Anisotropy of magnetic susceptibility data for a ferromagnetic granite (Godhra Granite, NW India) are presented and it is shown that the degree of magnetic anisotropy ( P ′) is not controlled by the mean susceptibility ( K m ). Analyses carried out across a high-strain zone lying between granite and adjacent gneiss show that P ′ values are highest in samples that lie close to the contact and decrease away from it. Based on these results it is concluded that if P ′ is not controlled by K m , then the former can be used to gauge strain-intensity variations in ferromagnetic granites.

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

“…AMS analysis of samples from 12 sites located at varying distance from the shear zone was carried out and it was observed that P 0 increases towards the shear zone. A relation between P 0 and distance from a shear zone was also noted by Sen et al (2005), who carried out AMS studies of samples of the Godhra Granite and associated banded gneiss located in the southern parts of Aravalli Mountain Belt (India). Samples were taken along an 18 m traverse cutting across a shear zone located at the contact between the two lithologies.…”

“…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.…”

“…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. Borradaile and Henry (1997), discussed result of AMS analysis of samples taken along a 10 m transect through a vertical shear zone near Rankin Inlet, Hudson's Bay (Canada).…”

“…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).…”

Structural and magnetic fabric studies of recess structures in the western Himalaya: Implications for 1905 Kangra earthquake

“…Figure 3 (Pj vs. K m plot) shows absence of one-to-one correlation between the two parameters. Hence P j and AMS fabric can be correlated with strain (Borradaile, 1987;Pares and van der Pluijm, 2002; Mukherji et al 2004;Sen et al 2005;Majumder and Mamtani, 2009;Mamtani and Sengupta, 2009). …”