Separation of Gagua Rise from Great Benham Rise in the West Philippine Basin during the Middle Eocene.

The West Philippine Basin (WPB) has started opening at ~ 58 Ma and ceased spreading at ~ 33 Ma, developing a fast spreading (~ 44 mm/yr half-spreading rate) magmatic episode between 58 and 41 Ma and the second amagmatic episode between 41 and 33 Ma. The occurrence of the first stage of spreading is closely related to the Oki-Daito mantle plume and related Benham Rise (BR) and Urdaneta Plateau (UP) activity. To the east of the Luzon-Okinawa Fracture Zone (LOFZ), BR was the most active volcanism from 48 to 41 Ma.