Anisotropy of magnetic susceptibility in the Almora crystalline zone lesser Himalaya, India: a case study

Abstract

The Almora Crystalline Zone (ACZ) in the Kumaun Lesser Himalaya is disposed in the form of a large thrust sheet over the unfossiliferous Precambrian-Palaeozoic sedimentary sequences and have tectonic contacts, known as North Almora Thrust (NAT) and South Almora Thrust (SAT). The rocks are metamorphosed under greenschist and amphibolite facies and contain mainly diamagnetic and paramagnetic minerals. The structural and fabric data collected from the field has been found to be matching with the newly generated magnetic data of crystalline rocks from the vicinity of the NAT and SAT. Anisotropy of Magnetic Susceptibility (AMS) measurements has become an important tool for fabric study based tectonic evolution of metamorphic terrains. These rocks show a very strong preferred orientation of lineation (kmax) and the mean shape of the strain ellipsoid is prolate due to the late stage thrust sheet movements. However, in places, a few samples show high mean susceptibility due to the presence of ferromagnetic minerals.