A review of localization of the deformation in Garhwal Himalaya: younging activation of shear zones from the metamorphic core of the belt towards the foreland

Recent studies highlighted that, starting from ~23 Ma onwards, deformation in Garhwal Himalaya (NW India) localized first in the inner part of the Greater Himalayan Sequence (GHS) along the Badrinath shear zone (BSZ) and subsequently along the Main Central thrust zone (MCTz), made by the upper Vaikrita thrust (VT) and the lower Munsiari thrust (MT). Detailed in-situ geochronology by U-Th-Pb on monazite and Ar / Ar on micas demonstrated that these 40 39 thrust-sense shear zones were active in different times from the older BSZ active at 23-21 Ma, through the VT 20-16 to 9-8 Ma up to the younger MT, active at 5-4 Ma. The consequences are twofold: a) all deformation in the MCTz was not active at the same time but in at different times, as deformation migrated from the upper levels to the lower levels of the GHS in few Myrs. In addition, the static growth of micas after deformation testifies that once deformation migrated to the lower shear zone levels, the levels, the deformation in the upper part ceased; b) the downward sequence of deformation demonstrates that the GHS and Lesser Himalayan Sequence were exhumed by an “in-sequence shearing” deformation resulting in the earlier exhumation of the upper portions of the metamorphic core.