Magmatism, Metamorphism, and Plate Tectonics Dynamics

Internal Processes: Magmatism and Plate Tectonics

High pressures subject the rocks, raising their melting point and keeping them solid.

Magma Generation Factors:

• An increase in temperature produced by friction.
• A drop in pressure, which lowers the melting point.
• The presence of fluid reduces the temperature required for fusion.

Fusion occurs where:

• Ridges and rifts cause the lithosphere to thin.
• Under hot spots, a hot plume rises to the surface, causing pressure to decrease and leading to melting.
• In subduction areas, friction and water-saturated sediments reduce the melting point of rocks.

Metamorphism and Plate Tectonics

Metamorphism is a process that transforms rocks due to increased pressure, temperature, or both factors, without causing fusion (isochemical process).

Types of Metamorphism:

• Contact Metamorphism: Produced by an increase in temperature.
• Regional Metamorphism: Produced by increased temperature and pressure.
• High-Pressure Metamorphism: Caused by increased pressure.

Metamorphic Environments:

• In Subduction Zones: Two metamorphic belts form: one beside the trench (due to the collision of two plates) and another in the volcanic chain (due to the rise of magmas).
• In Continental Collision Zones: Large areas of metamorphism occur where enormous pressures are compounded by heat generated from friction and the ascent of magmas.

Isostasy: Lithospheric Balance

Isostasy describes the floating balance between the lithosphere and the plastic mantle. If mass increases, the lithosphere tends to sink into the mantle; if mass is reduced, it tends to rise.

Movements Linked to Glaciation:

The burden of an ice sheet causes the continent to sink. When the ice melts, the continent rises, retrieving its initial equilibrium situation.

Movements Linked to Erosion and Deposition:

• Subsidence: When a great thickness of sediments is deposited in a sedimentary basin, the basin floor tends to sink.

Isostatic Response to Mountain Erosion:

1. Growth of a root under a mountain recently formed.
2. Beginning of erosion.
3. Lithosphere download (reduction) due to erosion.
4. Isostatic ascent in response to weight loss.