---
title: "Tectonic zones and major discontinuities"
subject: "Engineering Geology I"
chapter: 7
key: "semester_3/engineering_geology_i:tectonic-zones-and-major-discontinuities"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/tectonic-zones-and-major-discontinuities
site: BCT Engineering
---

# Tectonic zones and major discontinuities

Engineering Geology I · Chapter 7: Geology of Nepal

- Asked in: 2081 Baisakh, 4 marks; 2080 Baisakh, 3 marks (asked 2 times)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/tectonic-zones-and-major-discontinuities
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-7

## Question

Describe the tectonic zones and the major discontinuities (HFT, MBT, MCT) of the Nepal Himalaya.

## 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).

## Answer

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

```text
  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.

| 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 |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. The correct south-to-north order of discontinuities is:
   A. MCT, MBT, MFT, STDS
   B. STDS, MCT, MBT, MFT
   C. MBT, MFT, STDS, MCT
   D. MFT/HFT, MBT, MCT, STDS
   Answer: D. They separate Terai, Siwalik, Lesser, Higher and Tethys. (Key point: Ordering)

2. MFT/HFT is regarded as:
   A. Active (Holocene)
   B. Inactive since Precambrian
   C. Miocene only
   D. A normal fault
   Answer: A. MCT is Miocene and partly active. (Key point: Age)

3. The STDS is:
   A. A thrust between Terai and Siwalik
   B. A normal fault system between Higher Himalaya and Tethys zone
   C. A river
   D. A lake
   Answer: B. It is Miocene in age. (Key point: STDS)

4. Rocks of the Sub-Himalaya (Siwalik) are:
   A. Precambrian schist
   B. Granite
   C. Miocene to Pleistocene molasse sediments
   D. Quaternary alluvium
   Answer: C. Terai is Quaternary alluvium. (Key point: Sub-Himalaya rocks)

## Related in Engineering Geology I

- [Geology of Nepal; significance of HFT, MBT, MCT](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ageology-of-nepal-significance-of) — Engineering Geology I, chapter 7
- [Discontinuities and engineering problems in Nepal Himalaya](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Adiscontinuities-and-engineering-problems-in) — Engineering Geology I, chapter 7
- [Tectonic divisions of the Nepal Himalaya](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Atectonic-divisions-of-the-nepal) — Engineering Geology I, chapter 7, asked 4×
- [Discontinuities; Siwalik and Higher Himalaya lithology](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Adiscontinuities-siwalik-and-higher-himalaya) — Engineering Geology I, chapter 7
- [Tectonic division and Lesser Himalaya geology](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Atectonic-division-and-lesser-himalaya) — Engineering Geology I, chapter 7
- [Tectonic divisions with sketch and problems](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Atectonic-divisions-with-sketch-and) — Engineering Geology I, chapter 7, asked 4×

## Related in other subjects

- [Major discontinuity systems of Nepal Himalaya](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Anepal-discontinuity-systems) — Engineering Geology II, chapter 2, asked 12×