Tectonic divisions of the Nepal Himalaya

From south to north, Nepal is divided into five tectonic zones, separated by major thrusts and faults (discontinuities):

  S                                              N
  Terai | Sub-Him | Lesser Him | Higher Him | Tethys
        |(Siwalik)|            |            |
       MFT/HFT   MBT          MCT          STDS

1. Terai (Gangetic plain): Quaternary alluvium.
2. Sub-Himalaya (Siwalik zone): Miocene to Pleistocene molasse sediments.
3. Lesser Himalaya: Precambrian to Palaeozoic low-grade metamorphic rocks and sediments.
4. Higher Himalaya (Great Himalaya): high-grade metamorphic rocks and granites.
5. Tibetan-Tethys Himalaya: Palaeozoic to Cretaceous fossiliferous marine sediments.

Boundaries (major discontinuities)

• Main Frontal Thrust (MFT) / Himalayan Frontal Thrust (HFT): between the Terai and Siwalik.
• Main Boundary Thrust (MBT): between the Siwalik and Lesser Himalaya.
• Main Central Thrust (MCT): between the Lesser and Higher Himalaya.
• South Tibetan Detachment System (STDS): between the Higher Himalaya and the Tethys zone.

Short notes on the zones

• Terai: Quaternary alluvium; flat, flood-prone.
• Siwalik: weak sandstone, mudstone and conglomerate.
• Lesser Himalaya: phyllite, slate, quartzite, limestone, dolomite.
• Higher Himalaya: gneiss, schist, migmatite and granite.
• Tethys: fossiliferous limestone, shale, sandstone.