What geologic features might form at the surface of Plate A?
The correct answer and explanation is:
Correct Answer: Volcanic island arcs and oceanic trenches
At the surface of Plate A, if it is an oceanic plate converging with another oceanic or continental plate, the main geologic features likely to form are volcanic island arcs and deep oceanic trenches. These features are formed through the process of subduction, where one tectonic plate is forced beneath another.
When an oceanic plate such as Plate A converges with another oceanic plate, the older, denser plate subducts beneath the younger, less dense plate. As Plate A descends into the mantle, it heats up due to increased pressure and temperature. Water and other volatile materials in the subducting plate lower the melting point of the overlying mantle, causing it to partially melt. This molten rock, or magma, rises through the overriding plate and may erupt on the ocean floor, forming a chain of volcanic islands known as a volcanic island arc. A well-known example is the Mariana Islands in the western Pacific Ocean.
Along the boundary where Plate A is subducting, a deep oceanic trench forms. This trench marks the location where the oceanic plate bends and begins its descent into the mantle. One of the deepest oceanic trenches in the world, the Mariana Trench, was created by such subduction processes.
In cases where Plate A subducts beneath a continental plate, the resulting features at the surface include volcanic mountain ranges on land rather than island arcs. An example of this scenario is the Andes Mountains in South America, formed by the subduction of the oceanic Nazca Plate beneath the continental South American Plate.
These surface features are visible expressions of the immense forces involved in plate tectonics and provide important evidence of the dynamic processes shaping Earth’s crust.