GEOLOGICAL SOCIETY OF THE PHILIPPINES

 
 

Recent Offshore Data in South China Sea and West Philippine Basin: Implications to The Understanding of Philippine Tectonics

 

G.P. Yumul, Jr.1,2,3 and C.B. Dimalanta2

1 Department of Science and Technology, Taguig City
2 National Institute of Geological Sciences, College of Science, University of the Philippines
Diliman, Quezon City
3 Honorary SEG Lecturer, Society of Economic Geologists


 

Abstract

 

Recent work in the northernmost portion of the South China Sea and the West Philippines basin had revealed new information that are deemed important in understanding the geology and tectonic evolution of the Philippine island arc system. The northernmost boundary of the South China Sea revealed the presence of Eocene (37Ma) oceanic crusts (Hsu et al. 2004). Furthermore, a trapped Philippine Sea Plate has also been found north of the Eocene South China Sea, west-southwest of Taiwan. The existence of this Eocene oceanic crust and the recognition that spreading rates in the South China Sea had changed from 44mm/yr (half-spreading rate) to less than 30mm/yr (half-spreading rate) through time has tremendous implication on how we interpret the evolution of the western portion of the Philippines.

 

On the other hand, the existence of Cretaceous complexes in the West Philippine Basin has also been reaffirmed and reported recently. The West Philippine Basin is one of the sub-basins of the Philippine Sea Plate marginal basin. The other sub-basins are the Shikoku, Parece Vela and Mariana Trough. Although still controversial, the trapped Huatung Basin, east-southeast of Taiwan, is thought to be Cretaceous in age (Deschamps and Lallemand, 2002). Hickey-Vargas (2005) had recently reported the presence of Cretaceous igneous rocks in the Amami Plateau. Offshore geophysical work had also supported a back-arc basin setting for the Philippine Sea Plate marginal basin, rather than being a trapped oceanic crust (Okino and Fujioka 2003). All of these new data and information have tremendous implications on how the Philippine Mobile Belt, especially the eastern seaboard, had evolved through space and time.

 

 
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