Final answer:
Andesitic magma is typical at continental margins with subduction zones, formed by flux melting when oceanic crust subducts beneath continental crust, as exemplified by the Andes mountains.
Step-by-step explanation:
This type of magma is usually found at continental margins associated with subduction zones. The correct answer is b) Andesitic. Andesitic magma is common at continental margins where subduction zones are present.
When oceanic crust, which is typically mafic and leads to basaltic compositions, subducts beneath continental crust, the resultant melting produces magmas that are intermediate in composition - like andesite.
This process describes a situation where water released from the hydrated minerals in the subducting slab triggers flux melting, producing a magma that is less mafic than the oceanic crust but not as felsic as continental crust material.
Andesitic magma is therefore typical in volcanic regions along continental margins, such as the Andes mountain range in South America, which has a history of subduction-related volcanism.