A previously unknown tectonic plate — one that has been swallowed up by the Earth — has been discovered in the Philippine Sea, according to a recent study.
Using images constructed from earthquake data, geoscientists have developed a method for resurrecting a “slab graveyard” of tectonic plate segments buried deep within the Earth,unfolding the deformed rock into what it may have looked like up to 52 million years ago. This helped the researchers identify the previously unknown East Asian Sea Plate, where an ancient sea once existed in the region shortly after dinosaurs went extinct.
The Philippine Sea lies at the juncture of several major tectonic plates. The Pacific, Indo-Australian and Eurasian plates frame several smaller plates, including the Philippine Sea Plate, which researchers say has been migrating northwest since its formation roughly 55 million years ago. 
In the process, the Philippine Sea Plate collided with the northern edge of the East Asian Sea Plate, driving it into the Earth’s mantle. The southern area of the East Asian Sea Plate was eventually subducted by, or forced beneath, other neighboring plates, the researchers said.