Age-depth correlation of the Philippine Sea back-arc basins and other marginal basins in the world

Abstract

Statistical analysis of underway bathymetric profiles of the Philippine Sea back-arc basins; the Mariana Trough, the Shikoku Basin, the Parece Vela Basin and the West Philippine Basin reveals an age-depth correlation in the basins. The basement depths of the Philippine Sea range from 3200 to 6000 m with their ages from 0 to 60 Ma. The age-depth curve of the whole Philippine Sea can be represented by the following equation: Depth (m) = 3222 + 366√Age (Ma) The equation shows that the basement depth of the Philippine Sea is about 800 m deeper than that of the major ocean floors of the same age. The coefficient of 366 in this equation is close to that for major oceans, 350. This suggests that the cooling processes of the lithospheres in the Philippine Sea and major oceans are similar to each other, whereas the structure and composition of the deeper layers of the Philippine Sea seem to be different from those of major oceans. Our analysis of ETOP digital bathymetric data, however, indicates that this relationship does not hold for some other marginal basins. Marginal basins other than back-arc basins generally follow the age-depth curve of major oceans. Young back-arc basins ( <10 Ma) show a variety of the basement depth from shallower to deeper than major oceans and their basement depths are well correlated with dipping angles of the corresponding subducting slabs. Shallower back-arc basins are associated with more gently dipping slabs and deeper back-arc basins with more steeply dipping slabs. The back-arc basins older than 15 Ma, however, are always deeper than the major oceans and follow the age-depth curve of the Philippine Sea back-arc basins.