Abstract
We constructed a new free-air gravity anomaly map of the Philippine Sea Plate (PSP) using ship-tracked gravity data from the National Geophysical Data Center (NGDC). Our results show that the isogals trend correlates well with the tectonic structures in the PSP. After removing the gravity induced by sea water from the free-air gravity data, we obtained the regional Bouguer gravity anomaly, which is later used to compute the Moho geometry in the PSP by applying the Parker-Oldenburg iterative method. Our results indicate that in the southern part of the West Philippine Basin (WPB) the crustal thickness is nearly homogeneous with a value of about 5 km, which implies that the WPB is quite stable. The low-amplitude and near-zero free-air gravity anomalies clearly indicate that the whole WPB, except at trenches and island arcs, is nearly in a state of isostatic equilibrium. The average crustal thickness of the Palau Kyushu Ridge (PKR) is more than 10 km. In the eastern PSP the crustal thickness gradually increases eastward. Our results also imply that a relatively thin and low density mantle exists beneath the Parece Vela Basin (PVB) as a consequence of back-arc spreading and serpentinized upwells of the thin crustal thickness.
Highlights
The Philippine Sea Plate (PSP) is located in the western Pacific Ocean, bounded by the Pacific and Eurasian plates and within the latitude range 5 - 35°N and longitude range 120 - 150°E (Fig. 1)
We compiled a free-air anomaly map for the PSP which shows that the gravity anomaly over the PSP generally has a low amplitude and long wavelength with near-zero average values
The isogals trend is generally consistent with the geological structures and closely correlates with the PSP bathymetry
Summary
The Philippine Sea Plate (PSP) is located in the western Pacific Ocean, bounded by the Pacific and Eurasian plates and within the latitude range 5 - 35°N and longitude range 120 - 150°E (Fig. 1). Four subduction zones lie along the eastern PSP: the Izu-Bonin Trench (IBT), the Mariana Trench (MT), the Yap Trench (YT) and the Palau Trench (PAT) stretching from north to south. There are four subduction zones along the western PSP, which include the Philippine Trench (PT), the Manila Trench (MAT), the Ryukyu Trench (RT) and the Nankai Trough (NT). The interior of the PSP can be divided into three major basins: the Shikoku Basin (SB), the Parece Vela Basin (PVB) and the West Philippine Basin (WPB). Another prominent geological feature is the Palau Kyushu Ridge (PKR) with North-South trending (Fig. 1)
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