Kink band microstructures in Mica in the  Dafla Formation of the Siwalik Group of  rocks, West Kameng District, Arunachal  Pradesh

Tapos Kumar Goswami

Volume : II, Issue : XII, December - 2013

Kink band microstructures in Mica in the Dafla Formation of the Siwalik Group of rocks, West Kameng District, Arunachal Pradesh

Tapos Kumar Goswami

Abstract :

The Neogene Siwalik sequence of western Arunachal Pradesh comprises northward dipping thrust sheets structurally below the Main Boundary Fault (MBT) and above the Main Frontal Thrust (MFT). In the foreland propagating thrust package, the compact and micaceous Dafla sandstone -shale-clay stone sequence is thrusted over the semi consolidated Subansiri sandstone -clay sequence. Near the zone of cataclasis the micaceous Dafla sandstones show microscale kink folds. These kink bands verge in the same direction of the vergence of the mesoscale folds in the Dafla sandstones. Both mobile and fixed hinge kink bands are observed showing lot of variation in the angles. At the initial stage the high water pressure under elevated confining pressure may play a vital role in the development of these kink bands. At the initial diagenetic temperature where mica shows considerable ductility the quartz and feldspar grains show ittle fracturing in response to the compression parallel to the (00)1 basal plane of mica.