Subduction of oceanic plates:
Oceanic plates, which are composed mainly of basaltic rocks, carry water in the form of hydrated minerals within their structure. As these plates move towards a convergent plate boundary, they descend into the Earth's mantle through a process called subduction.
Dehydration of subducted slabs:
As the subducted oceanic plates descend into the mantle, they experience increasing pressure and temperature. This can cause dehydration reactions to occur within the hydrated minerals, releasing water into the surrounding mantle rocks. The released water migrates upwards through the mantle due to its lower density compared to the surrounding minerals.
Role of aluminum-enriched slabs:
Aluminum-enriched hydrated slabs are believed to play a significant role in water delivery to the mantle because aluminum can enhance the stability of hydrous minerals within the subducted slabs. These minerals, such as amphibole and phlogopite mica, can remain stable at higher pressures and temperatures compared to hydrous minerals that are not aluminum-enriched. As a result, aluminum-enriched slabs can carry more water into the mantle before undergoing dehydration reactions.
Additionally, aluminum-enriched slabs can also influence the melting behavior of the mantle rocks they interact with. The presence of aluminum can lower the melting temperature of the surrounding mantle material, leading to partial melting and the formation of hydrous magmas. These magmas may eventually rise and erupt at the Earth's surface, releasing water into the atmosphere or hydrosphere.
Therefore, subduction of aluminum-enriched hydrated slabs represents a potential mechanism for transporting water from the Earth's surface into the mantle. The delivery of water to the mantle is important for understanding various geological processes, such as magma generation, volcanic activity, and the dynamics of plate tectonics.
