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 subducted slabs, releasing water (H2O) and other volatiles such as carbon dioxide (CO2) and methane (CH4).
Aluminum enrichment in subducted slabs:
Some studies suggest that subducted oceanic crust may become enriched in aluminum (Al) during subduction. This can occur through various mechanisms, such as the release of Al-rich fluids from the slab or the alteration of minerals within the slab by fluids derived from the surrounding mantle.
Transport of water by Al-enriched slabs:
Aluminum-enriched subducted slabs have the potential to transport significant amounts of water into the mantle. This is because aluminum can bind with water to form stable minerals, such as amphibole and chlorite. These minerals can incorporate significant amounts of water in their crystal structures, effectively trapping the water within the slab.
Melting of subducted slabs:
As the subducted slab descends further into the mantle, it may encounter conditions where the temperature and pressure are high enough to cause partial melting. This melting can produce magmas that may rise back towards the surface through volcanic activity. Some of these magmas may carry dissolved water derived from the hydrated minerals within the subducted slab.
Therefore, aluminum-enriched hydrated slabs can act as important carriers of water into the Earth's mantle. The water and other volatiles released from these slabs play a crucial role in various geological processes and contribute to the water budget of the planet.
