1. Decompression Melting:
* As tectonic plates move apart at divergent boundaries, the pressure on the underlying mantle decreases.
* This decrease in pressure causes the mantle rock to partially melt, a process known as decompression melting.
* The resulting magma is basaltic in composition.
2. Mantle Upwelling:
* The separation of plates creates a gap that allows hot, less dense mantle material to rise towards the surface.
* This upwelling mantle material is typically basaltic in composition.
3. Lower Melting Point of Basalt:
* Basaltic magma has a relatively lower melting point compared to other types of magma.
* This means that basaltic magma is more likely to form under the lower pressure conditions found at divergent boundaries.
4. Formation of Mid-Ocean Ridges:
* The upwelling of basaltic magma at divergent boundaries leads to the formation of mid-ocean ridges, underwater mountain ranges that mark the location of plate separation.
* These ridges are characterized by extensive basaltic volcanism.
5. Formation of Oceanic Crust:
* The solidified basaltic magma forms new oceanic crust, which is constantly being created at divergent boundaries.
Summary:
The combination of decompression melting, mantle upwelling, and the relatively lower melting point of basalt makes these volcanic rocks the primary product of divergent plate boundaries. This process results in the formation of mid-ocean ridges and the continuous creation of oceanic crust.
