The Upper Lahul region in the NW Himalaya is located in the transition
zone between the High Himalayan Crystalline (HHC) to the SW and the
Tethyan Zone sedimentary series to the NE. The tectonic evolution of
these domains during the Himalayan Orogeny is the consequence of a
succession of five deformation events. An early D1 phase corresponds to
synmetamorphic, NE verging folding. This deformation created the Tandi
Syncline, which consists of Permian to Jurassic Tethyan metasediments
cropping out in the core of a large-scale synformal fold within the HHC
paragneiss. This tectonic event is interpreted as related to a NE
directed nappe stacking (Shikar Beh Nappe), probably during the late
Eocene to the early Oligocene. A subsequent D2a phase caused SW verging
folding in the HHC. This deformation is interpreted as contemporaneous
with late Oligocene to early Miocene SW directed thrusting along the
Main Central Thrust. In the Tethyan Zone, a D2b phase is marked by a
decollement thrust, a system of reverse faults, and gentle folds,
associated with SW directed tectonic movements. This deformation is
related to an imbricate structure, characteristic of a shallow
structural level, and developed in the frontal part of a nappe affecting
the Tethyan Zone units of SE Zanskar (Nyimaling-Tsarap Nappe). A later
D3 phase generated the Chandra Dextral Shear Zone (CDSZ), a large-scale,
ductile, dextral strike-slip shear zone, located in the transition zone
between the HHC and the Tethyan Himalaya. The CDSZ most likely
represents a part of a system of early Miocene extensional and/or
dextral, strike-slip shear zones-observed at the HHC-Tethyan Zone
contact along the entire Himalaya. A final D4 phase induced large-scale
doming and NE:verging back folding.