The geologic structure that arises from the subduction of oceanic lithosphere under a continental block is called a magmatic arc.

Here's a breakdown:

* Subduction: The denser oceanic plate sinks beneath the less dense continental plate.

* Volcanic arc: As the oceanic plate descends, water trapped within its minerals is released into the overlying mantle. This water lowers the melting point of the mantle rock, leading to the formation of magma. This magma rises to the surface, creating a chain of volcanoes known as a volcanic arc.

* Igneous plutons: Some magma cools and crystallizes underground, forming intrusive igneous bodies called plutons. These plutons can be massive and contribute to the uplift and deformation of the surrounding continental crust.

In summary, the subduction zone is the birthplace of magmatic arcs, characterized by volcanic arcs and associated igneous plutons.