Question

Describe three processes that generate magma in the asthenosphere.

Short answer

Magma is generated by decompression melting, addition of volatiles, and heat transfer.

Step-by-step solution

Decompression Melting

Magma in the asthenosphere can be generated through decompression melting. This occurs when hot mantle rock rises toward the Earth's surface. As it ascends, the pressure decreases more rapidly than the temperature, which lowers the melting point of the rock, causing it to melt and form magma.

Addition of Volatiles

Another process that generates magma is the addition of volatiles, such as water and carbon dioxide, to the mantle rock. These volatiles decrease the melting point of the rock by modifying its chemical structure, which results in partial melting and the production of magma.

Heat Transfer

The transfer of heat from hotter to cooler rock can also generate magma. When hot magma invades cooler mantle rock, the heat can cause the rock's temperature to reach its melting point, leading to partial melting. This addition of heat can produce sufficient temperatures to create new magma.

Key concepts

Decompression Melting

Decompression melting is a fascinating process that occurs deep within the Earth. As mantle rock ascends towards the surface, the pressure around it decreases significantly faster than the temperature. This rapid pressure reduction lowers the melting point of the rock, causing it to melt and transform into magma. This process is one of the primary ways magma is generated within the asthenosphere.
- An essential aspect of decompression melting is its reliance on mantle convection currents. - As hot, buoyant mantle rock rises, it retains its heat but loses pressure, making it easier for the rock to melt. - Decompression melting typically occurs at mid-ocean ridges and hot spots, where mantle rock is able to ascend without losing much heat to its surroundings.
Understanding decompression melting can help geologists explain the formation of new oceanic crust and volcanic activity at various tectonic settings.

Addition of Volatiles

The addition of volatiles is another intriguing phenomenon that contributes to magma formation. Volatiles, such as water and carbon dioxide, play a crucial role in modifying the chemical composition of mantle rock, leading to a decrease in its melting point. When these volatiles are introduced into the mantle, they disrupt the mineral bonds, facilitating partial melting. - This process often happens in subduction zones, where oceanic plates are forced under continental plates. - The subducting plate carries water and other volatiles into the mantle, where they are released into the overlying mantle wedge, triggering melting. - Addition of volatiles is essential for generating explosive volcanic eruptions, as the presence of volatiles lowers the melting point and creates more fluid magma.
The study of volatile addition is fundamental in understanding the behavior of subduction-related volcanism and the formation of volcanic arcs.

Heat Transfer in Asthenosphere

Heat transfer within the asthenosphere is a significant process that leads to the generation of magma. This happens when hot magma or mantle plumes invade cooler mantle rock. As the heat transfers from the hotter regions to cooler ones, it can increase the temperature of the surrounding rock to its melting point, resulting in partial melting and the formation of new magma. - This process is prominent where large magma bodies or plumes from deep within the Earth come into contact with the cooler surrounding rock. - Heat transfer is crucial in creating a thermal gradient, where the difference in temperature facilitates the melting of mantle rock. - It plays a vital role at convergence zones and continental rift zones where deep-sourced magma bodies rise into cooler lithospheric structures.
By studying heat transfer processes in the asthenosphere, geoscientists can gain insights into the creation of magmatic intrusions and volcanic regions.