Abstract
The Huatung Basin is a small oceanic basin located east of Taiwan. Previous age estimates from magnetic lineationstudies indicated an Eocene age for the basin, and formation from the Central Basin Spreading Center of the WestPhilippine Basin during the last phase of spreading in Middle Eocene. New Ar/Ar ages obtained on gabbros dredged onoceanic basement highs of the Huatung Basin are Early Cretaceous. These old ages are consistent with Early Cretaceousages determined on radiolarian assemblages from Lanyu Island (Luzon Arc). We have performed magnetic anomaliesmodeling for an Early Cretaceous oceanic crust. Our results are in good agreement with new Ar/Ar ages determinations.The best fit is indeed obtained with an opening of the Huatung Basin during the Early Cretaceous from 131 to 119 Ma,with a half spreading rate varying between 25 and 30 mm/yr. The spreading center appears to be located south of theactual basin. The abnormal depth (5500 m instead of 5900 m) and thickness (V12 km instead of 6 km) of the crustbeneath the basin indicate that there was probably an excess supply of magma during its formation. We propose thatthe basin is a fragment of the former `proto-south China Sea' or possibly the `New Guinea Basin' that has been trappedby the Philippine Sea Plate.