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Tectonic zones and major discontinuities
Short answer
Nepal has five zones from south: Terai (alluvium), Siwalik (molasse), Lesser Himalaya (low-grade metasediments), Higher Himalaya (high-grade gneiss/granite), and Tethys (fosiliferous sediments). Major discontinuities are MFT/HFT (Terai-Siwalik), MBT (Siwalik-Lesser Himalaya), MCT (Lesser-Higher), and STDS (Higher-Tethys).
Describe the tectonic zones and the major discontinuities (HFT, MBT, MCT) 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
- Terai (Gangetic plain): Quaternary alluvium.
- Sub-Himalaya (Siwalik zone): Miocene to Pleistocene molasse sediments.
- Lesser Himalaya: Precambrian to Palaeozoic low-grade metamorphic rocks and sediments.
- Higher Himalaya (Great Himalaya): high-grade metamorphic rocks and granites.
- 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.
| Thrust | Between | Tentative location | Age of last movement |
|---|---|---|---|
| MFT / HFT | Terai and Siwalik | Along the southern foot of the Churiya hills | Active (Holocene) |
| MBT | Siwalik and Lesser Himalaya | Along the northern edge of the Siwaliks / foot of the Mahabharat range | Late Pleistocene, reactivated |
| MCT | Lesser and Higher Himalaya | Along the foot of the Higher Himalaya, mostly north of Kathmandu | Miocene, partly active |
| STDS | Higher Himalaya and Tethys | Along the northern slopes of the Great Himalaya | Normal fault, Miocene |
✓ Answer checked by Claude Opus 5.5 (high effort)
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