Presentation 6 Igneous rocks 2025

## Introduction to Rocks
- Rocks are categorized into three main groups:
- **Igneous Rocks**: Formed from magma.
- **Sedimentary Rocks**: Formed from deposition due to water, wind, or ice.
- **Metamorphic Rocks**: Altered from existing rocks under high temperature and pressure.

## Igneous Rocks
- Focus: Formation, environments, and characteristics of igneous rocks.

### Formation Environments
- **Two Primary Environments for Igneous Rock Formation**:
- **Divergent Margins**: Mid-ocean ridges, continental rifts.
- Rocks melt via **decompression melting** (lowering pressure).
- **Subduction Zones**: Water addition leads to melting.
- Rocks melt through **hydration melting** (addition of water).

### Melting Phase Diagrams
- **Phase Diagrams**: Show stability fields of different phases of a material.
- Example with Water (H2O)
- Triple Point: Where solid, liquid, and vapor phase coexist.
- Water uniquely has a negative slope between solid and liquid phases.
- The pressure affects states, leading to potential transformations (e.g., ice to water).

### Melting Mechanisms
1. **Decompression Melting**
- Occurs as mantle rock rises and pressure decreases without temperature increase.
- Important in:
- **Mid-Ocean Ridges**: Create new oceanic crust (basaltic magma).
- **Continental Rifts**: Similar melting process occurring within continents (e.g., East African Rift).
- **Mantle Plumes**: Hotspots where rock rises from deep within the Earth (e.g., Hawaii).

2. **Hydration Melting**
- Takes place in subduction zones: Water lowers melting points.
- Leads to higher silica magmas (e.g., Andes).
- Results in diverse magma compositions and eruptive styles.

### Bowen's Reaction Series
- Classification based on mineral crystallization as temperature decreases.
- **Basaltic Rocks (