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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 40 39 thrust (MT). Detailed in-situ geochronology by U-Th-Pb on monazite and Ar / Ar on micas demonstrated that these 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.

A newly identified high-temperature shear zone, the Badrinath shear zone (BSZ), is described within the metamorphic core of the Himalayan belt along the Alaknanda valley, Garhwal Himalaya (NW India). A multidisciplinary approach comprising fieldwork, microstructural analyses, petrology and in situ monazite geochronology was addressed to this high-strain zone to better understand its role in the Greater Himalayan Sequence (GHS) evolution along the study area. The Badrinath mylonite displays top-to-the-south thrust-sense of shear and affects sillimanite-bearing gneiss showing evidence of partial melting. The data integration allowed us to reconstruct the following model for BSZ development: the pre-mylonitic stage took place during prograde metamorphic path reaching conditions of 700–720 °C and 10 kbar during the time interval of 34 and 23 Ma, with incipient partial melting, followed by nearly-isothermal decompression triggered by the shear activity between 23 and 19 Ma, with exhumation rate of ±0.3 cm yr−1. Moreover, the rocks from the lower part of GHS, in the BSZ footwall, experienced metamorphic conditions of c. 660–700 °C and c. 10–11 kbar, the partial melting and exhumation took place ~3 Ma after the BSZ. Such findings led us to correlate the BSZ with the High Himalayan Discontinuity (HHD) of Central Himalaya. The BSZ is the first reported HHD branch in NW Himalaya (Garhwal). It corroborates the regional extent of the HHD accomplishing an important role during the GHS exhumation. In the Alaknanda valley, the BSZ activity accommodated deformation during early exhumation stages, 3 Ma before the MCTz and STDS coeval motion took place. Our observations point to a shift in time and place of the deformation responsible to trigger the GHS exhumation.