Geology of Nepal

[1] About 800 km (500 mi) of this extent is in Nepal; the remainder includes Bhutan and parts of Pakistan, India, and China.

[4] Immediately prior to the onset of the Indo-Asian collision, the northern boundary of the Indian shield was likely a thinned continental margin on which Proterozoic clastic sediments and the Cambrian ±Eocene Tethyan shelf sequence were deposited.

[5] From south to north, it can be divided into five latitudinal morpho-tectonic zones and these are : The gangetic plain is also called the Terai which is a rich and fertile land in the southern parts of Nepal.

It is the Nepalese extension of the Indo-Gangetic Plains, which covers most of northern and eastern India, the most populous parts of Pakistan, and virtually all of Bangladesh.

The upward coarsening sequence of the sediments obviously exhibit the time-history in the evolution and growth of the Himalaya during the early Tertiary time.

[8] The Sub Himalayan zone is the 10 to 25 km wide belt of Neogene Siwaliks (or Churia) group rocks forming the topographic front of the Himalaya.

It rises from the fluvial plains of the active foreland basin, and this front generally mapped as the trace of the Main Frontal Thrust (MFT).

[9] Palaeocurrent and petrographic data from the sandstone and conglomerate indicate that these rocks were derived from the fold-thrust belt, and deposited within the flexural foredeep of the Himalayan foreland basin.

The Lesser Himalayas is made up mostly of unfossiliferous sedimentary and metasedimentary rocks; such as shale, sandstone, conglomerate, slate, phyllite, schist, quartzite, limestone and dolomite.

The highest-grade rocks (kyanite and sillimanite gneisses) are found within the MCT shear zone, i.e. upper Lesser Himalaya.

[23] The northern part is marked by the North Himalayan Normal Fault (NHNF), which is also known as the South Tibetan Detachment system (STDS).

The protolith of the HHC is interpreted to be Late Proterozoic clastic sedimentary rocks deposited on the northern Indian margin.

The area north of the Annapurna and Manaslu ranges in central Nepal consists of metasediments that overlie the Higher Himalayan zone along the South Tibetan Detachment system.