1. Structure and Origin of the Alpine–Himalayan Belt**

### **Origin**

* The **Alpine–Himalayan Belt** is the world’s most extensive **young folded mountain system**, stretching for about **15,000 km** from the **Atlantic (Iberian Peninsula, Alps, Carpathians)** through the **Middle East (Zagros, Caucasus, Taurus)** to the **Himalayas in Asia**.
* It formed mainly during the **Cenozoic Era (65 Ma onwards)** due to the **closure of the Tethys Ocean** and subsequent **collision of continental plates**.
* The **African, Arabian, and Indian plates** collided with the **Eurasian plate**, causing large-scale compression, crustal shortening, thrusting, and uplift.

### **Structure**

The belt consists of several **orogenic zones**:

1. **The Alpine System (Europe):** Alps, Carpathians, Apennines.
2. **The Middle Eastern System:** Zagros, Caucasus, Taurus.
3. **The Himalayan System:** Himalayas and adjoining ranges.

**Common Structural Features:**

* **Fold-and-thrust belts** (intense folding, nappes, thrust faults).
* **Metamorphic zones** and **granitic intrusions**.
* **Suture zones** marking the closure of Tethys (e.g., Indus–Tsangpo Suture Zone in Himalayas).
* **Foreland basins** in front of mountain belts (e.g., Indo–Gangetic Basin).

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## **2. Evolution of the Indo–Gangetic Basin**

### **Origin**

* The **Indo–Gangetic Basin (Indo–Gangetic Plain)** is a large, linear **foreland basin** lying south of the Himalayas.
* It formed due to **flexural downwarping of the Indian plate** under the enormous load of the rising **Himalayan orogen** during the **Cenozoic Era**.
* It represents the **peripheral depression** that developed as the Indian lithosphere flexed in response to the thrust loading from the Himalayas.

### **Stratigraphy and Sedimentation**

* The basin has been filled with a thick succession (up to **6,000 m**) of **Tertiary and Quaternary sediments** derived from the Himalayas.
* **Siwalik Group (Miocene–Pleistocene):** Coarse clastics deposited in molasse basins.
* **Recent Alluvium (Holocene):** Sands, silts, clays deposited by Indus, Ganga, and Brahmaputra river systems.

### **Present-day Significance**

* Forms the most fertile agricultural belt of India (the “Granary of India”).
* Hosts significant **groundwater resources**.
* Represents a natural record of **Himalayan uplift and erosion history**.

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## **Summary**

* The **Alpine–Himalayan Belt** is a major **Cenozoic mountain chain** formed by the collision of Africa, Arabia, and India with Eurasia, closing the Tethys.
* The **Indo–Gangetic Basin** originated as a **foreland basin** due to the load of the Himalayas on the Indian plate and is filled with thick Tertiary–Quaternary sediments, shaping present-day fertile plains.