What kind of magma is generally produced at mid-ocean ridges?

Basaltic magma is the primary type of magma produced at mid-ocean ridges due to the processes occurring at these divergent tectonic plate boundaries. As tectonic plates move apart, the reduction in pressure allows mantle rock to partially melt, forming this type of magma, which is relatively low in viscosity and rich in iron and magnesium.

Basalt is characterized by its lower silica content compared to andesitic or rhyolitic magmas, reflecting the composition of the mantle source material. This leads to the formation of new oceanic crust as the basaltic magma erupts onto the ocean floor, solidifying to create features like the mid-ocean ridge itself. The basaltic composition is integral to the geology of oceanic plates and is a key factor in understanding the dynamics of seafloor spreading, making it the correct choice in this context.

In contrast, andesitic and rhyolitic magmas are typically associated with more complex tectonic settings, such as subduction zones, where the involvement of continental crust and volatiles alters the magma’s composition. Volcanic ash is a byproduct of explosive volcanic eruptions, usually related to more viscous magmas, but it is not a type of magma itself.