The referred in literature as Larji-Kullu-Tectonic Window (LKTW, Fig.1)

The Himachal
Himalaya is known to have a complex
tectonic setting that has evolved during the Cenozoic era (Webb
et al. 2011). The Kullu valley, occurring between 31° 21′ N and 32°
59’N latitude and 76° 49′ E and 78° 59′ E longitude, with an area of 4782 km2 (falling in Survey of India Quadrangle sheet No 52H and 53E), is a prominent tectonic window referred in literature as Larji-Kullu-Tectonic Window (LKTW, Fig.1) (Heim and Gansser 1939; Le
Fort 1996; Hodges 2000; Yin 2006; Upreti 1999; Thakur 1998; Webb et al. 2007). The LKTW has structurally evolved in four phases during Early
Miocene to Pleistocene, where the Greater Himalayan Crystalline Sequence (GHCS) of rocks are brought over the units of Lesser Himalayan
Crystalline Sequence
(LHCS) rocks along the Main Central Thrust (MCT), and the window has been geomorphologically carved out and exhumed
during late phases
of movement spanning
across Pliocene- Pleistocene and Recent times (Vannay et al. 2004; Yin 2006; Remington M. Leger et al. 2013). The present study
area lies in the north-western part of LKTW, where the MCT tectonically juxtaposes rocks of the Higher Himalayan
Sequence with the Lesser Himalayan Sequence.

LKTW, the par-autocthnous structure (Dubey and Bhat 1991), is characterized by an antiformal fold structure in LHCS circumscribed by two prominent
thrusts MCT-I (Vaikrita Thrust) and MCT-II (Kullu thrust) with the axial zone of the fold trending NNW-SSE. The most conspicuous feature of the area is the presence of “Window in Window” structure, where a
20 km long and 6 km wide, lozenge-shaped “Larji window”
is bound by Banjar thrust and this Larji window lies within a larger window structure bounded by the Kullu Thrust (Fig- 2).  In addition,
the Munsiari Thrust, the thrust/fault line of regional
importance in the Himalayas
also traverses

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the area along the axial zone of Kullu Window (KW) and it has been described as an out-of-sequence thrust (OOST: Thiede 2004).


The present
day topography was developed by the last
phase of thrusting activity in this region. Recent seismic events clustering data indicates
that SW-directed thrusting
is still going on along the Munsiari
Thrust in the Garhwal
region (Kayal 1996), and at the same time east-directed extension is taking place in the MCT hanging wall in the Sutlej section
of the Larji-Kullu Tectonic window
(Molnar and Lyon-Caen 1989; Vannay
2004). The morpho-tectonic features
and a number of seismic events of moderate
magnitude in the region indicate active tectonic
movement in the Larji-Kulu Tectonic
Window (Dubey et al. 2003).


The Kullu Valley is characterized by highly variable lithology
consisting of a dominant
assemblage of low to high grade meta-sedimentary rocks belonging to different litho-tectonic groups. The upper part of the valley consists of gneisses,
granites and migmatites of the Vaikrita Group, locally
designated as the Rohtang
Gneissic Complex.
Micaceous Slates, garnetiferous quartzite and schist, green massive quartzite
and limestone of the Jutogh Group (in pockets limestones of Shali Formation as well) lie in the middle part. The Lesser Himalayan Sequence
consists of at least two tectono-metamorphic units: (i) The very low- to medium-grade Proterozoic meta-quartzites, shales, dolomites
and meta-igneous rocks (Frank et al. 1973, 1977; Miller et al. 2000) of the Lesser Himalayan Sedimentary Succession and (ii) the amphibolite-facies ortho- and paragneisses of the Lesser Himalayan Crystalline Unit (LHC),
i.e. the Jeori–Wangtu granitic
gneisses (Thiede
et al. 2004; Thoni et al. 2012). Geomorphologically, the area is characterized by high relief and variable degrees
of dissection with deep narrow gorges, steep slopes,
escarpments and cliff faces. The relief of the area varies in altitude
between 900 m to above 5000 m msl at Rorung Dhar. The upper reaches with high relief zone is mainly characterized by funnel-shaped valley with steep and variable slope
elements and also it is under the influence
of seasonal snow and mass movement
activity. The steepness of the topography can be judged from the fact that the altitude
rises from about 2000m near Manikaran
to about 5000m on Rorung Dhar within a distance of about 8 km and also experiences heavy snowfall. The middle reaches
of the Beas valley constitutes and characterized by wide open valleys, large alluvial fans, fluvial terraces
and flood plains belonging to the Quaternary period.               This area is drained
by Beas River and its tributaries viz Parvati,
Hurla, Sainj and Tierthan rivers joining Beas from the east. The Beas River, flowing southerly, transects
the area, with stream
base level ranging from 2800m
in the north to 900m in the south. The river is characterized by fluvio-glacial Quaternary alluvial deposits with three to four levels of fill and cut-fill
terraces (Sah and Mazari 2007). Bajada fans of large dimension
are seen on the eastern bank of the river offering
suitable space for urban development. Near Bhuntar, the channel changes its course from north- south to south-east direction where the process
channel avulsion
of about 45m is noticed.
However, the three sub-parallel tributaries (viz Parvati, Sainj
and Hurla) on the eastern
flank are primarily
bedrock rivers with unpaired strath
terraces. The Parvati
River, the main tributary of Beas is flowing
in E-W direction with the elevation drop from 4500 to 1090 m above msl. Climatically, the upper Beas basin experiences a subtropical to temperate type of climate.
The uppermost part of the Beas basin
experiences cold temperate
conditions, whereas temperate and subtropical conditions prevail
in the middle and lower zone. The rainfall pattern
clearly demonstrates that the influence
on precipitation is altitude
depended within the basin. The upper reaches of the



Beas basin experience more rainfall as compared to the lower as indicated by the average rainfall
distribution curve for the years
of 1983, 2004 and 2015.