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. |