Decompression Melting

Definition

Decompression melting is the process where a decrease in pressure allows magma to form from solid rock, typically occurring in the Earth's mantle. As tectonic plates move apart or when hot rock rises, the pressure decreases, which can lead to the melting of the rock without the addition of heat. This phenomenon is crucial for understanding magma generation, especially in relation to volcanic activity and plate tectonics.

5 Must Know Facts For Your Next Test

1. Decompression melting primarily occurs at divergent boundaries where tectonic plates are moving apart, leading to a drop in pressure as magma rises.
2. This process can generate basaltic magma, which is typically less viscous and leads to effusive eruptions when it reaches the surface.
3. Decompression melting plays a significant role in creating new oceanic crust at mid-ocean ridges, contributing to seafloor spreading.
4. The presence of water and other volatiles can lower the melting point of rocks, enhancing decompression melting in certain geological settings.
5. Understanding decompression melting helps explain why certain areas experience more frequent volcanic activity compared to others.

Review Questions

• How does decompression melting contribute to magma generation at divergent plate boundaries?
  • At divergent plate boundaries, tectonic plates are moving away from each other, which causes a decrease in pressure on the underlying mantle rocks. This reduction in pressure allows the solid mantle to partially melt without the need for additional heat, resulting in the formation of magma. The newly generated basaltic magma rises toward the surface, creating new oceanic crust and often leading to volcanic activity at mid-ocean ridges.
• Analyze the role of decompression melting in explosive versus effusive eruptions.
  • Decompression melting tends to generate basaltic magma, which is low in viscosity and typically results in effusive eruptions characterized by lava flows rather than explosive events. In contrast, more explosive eruptions are usually associated with magma that has higher viscosity and contains significant amounts of gas, such as andesitic or rhyolitic magmas. While decompression melting itself may not directly lead to explosive eruptions, it contributes to the overall magma generation process that influences eruption styles based on magma composition and gas content.
• Evaluate how understanding decompression melting can impact our predictions of volcanic activity at divergent plate boundaries.
  • Understanding decompression melting is vital for predicting volcanic activity because it provides insights into the processes that generate magma at divergent plate boundaries. By studying tectonic movements and pressure changes in these areas, scientists can anticipate when and where magma might reach the surface. Additionally, recognizing how decompression affects magma composition allows researchers to evaluate potential eruption styles and risks associated with new volcanic formations along mid-ocean ridges.

Related terms

Magma Generation: The process by which molten rock is formed in the Earth's crust and mantle, often through mechanisms like decompression melting or the addition of volatiles.

Volcanic Arc:

A series of volcanoes formed at a convergent plate boundary, where one tectonic plate is subducted beneath another, often resulting from decompression melting of the mantle.

Plate Tectonics:

The scientific theory explaining the movement of the Earth's lithosphere, which leads to the formation of various geological features, including mountains and volcanoes, largely driven by processes like decompression melting.