1. Decompression Melting:
* As tectonic plates move apart at divergent boundaries, the space between them is filled with rising magma from the asthenosphere (the upper layer of the mantle).
* This rising magma experiences a decrease in pressure as it moves towards the surface.
* The decrease in pressure lowers the melting point of the mantle rocks, causing them to melt.
2. Water Content:
* The mantle rocks at divergent boundaries are often enriched in water, which is released from the subducting plate at convergent boundaries.
* Water lowers the melting point of rocks, making them more susceptible to melting.
* This water is incorporated into the rising magma, contributing to its fluidity and explosiveness.
3. Heat Transfer:
* The rising magma from the asthenosphere transfers heat to the surrounding mantle rocks.
* This heat can also contribute to the melting of the mantle rocks, especially if they are already close to their melting point due to decompression or water content.
Overall, the combination of decompression, water content, and heat transfer creates the conditions necessary for mantle rocks to melt at divergent boundaries. This molten rock then rises to the surface, forming new crust and driving the process of seafloor spreading.
