Final answer:
The Mariana Subduction Zone is a geological boundary where the Pacific Plate is being subducted beneath the Philippine Plate. It contributes to significant geological activities like earthquakes and the formation of deep ocean trenches.
Step-by-step explanation:
In the context of the Mariana Subduction Zone, located at the boundary between the Pacific Plate (PA) and the Philippine Plate (PH), it is the Pacific Plate that is being subducted beneath the Philippine Plate. Subduction zones are tectonic plate boundaries where one plate moves under another and is forced into the mantle. This process causes some of the most significant geological events on Earth, including earthquakes and volcanic activity. In the Mariana Trench, the Pacific Plate dives beneath the Philippine Plate, creating one of the deepest parts of the ocean. Subduction at this zone not only leads to deep sea trenches but also has implications for the creation of island arcs and seismic activity in the region. The ongoing subduction also recycles the oceanic crust by melting it into the mantle where it can be reformed at rift zones, maintaining a balance in the Earth's crustal features.