Plate boundary processes of the Caroline Plate

The tectonic evolution of the Caroline Plate during the Oligocene to Early Miocene was mainly controlled by two fulcrums.The west fulcrum at Palau Island remained fixed during 29-25 Ma as the Ayu Trough rifted and produced the abyssal hills parallel to its boundaries,and the Pacific Plate and part of the Caroline Plate subducted to the north.At the northeast corner of the Caroline Plate,the east fulcrum is surrounded by a series of arc seamount chains.These chains resulted from the convergence between the Caroline Plate and the Pacific Plate and crustal softening of the northeastern Caroline Plate induced by the Caroline Hotspot at~25 Ma.This softening of the crust also led to the dysfunction of the east fulcrum,and the west fulcrum migrated south,which caused dextral motion along the Ayu Rift and the development of an en echelon structure.The Yap Trench was a part of the spreading center in the Parece-Vela Rift at~29 Ma.However,sinistral motion along the Parece-Vela Rift at around 20-15 Ma led to the exposure of the subducted Yap Trench and left a triangular region with distinctive geophysical characteristics in the surrounding area.