Final answer:
Ultra mafic and mafic magmas come from a mantle source, mainly at divergent plate boundaries like mid-ocean ridges through processes such as decompression melting.
Step-by-step explanation:
Ultra mafic and mafic magmas originate from a mantle source. These magmas are generally associated with tectonic plate boundaries where certain processes such as decompression melting and the addition of heat can cause the mantle material to melt.
For instance, at mid-ocean ridges, which are a type of rift zone, upwelling mantle material undergoes decompression melting due to reduced pressure as the plates pull apart, producing mafic magma that forms the oceanic crust.
Similarly, at subduction zones, the subduction of oceanic crust can introduce volatiles such as water into the mantle, which lowers the melting point and can produce magma; however, the magma generated at subduction zones is not ultra mafic or mafic in nature, but more commonly andesitic or even rhyolitic due to the interaction with crustal materials.