The Oceanic Crust Age Modelling Of The West Philippine Sea Basin Based On The Gravity And Magnetic Data And Its Evolution

The Philippine Sea plate is one of the most respective continental margin plates. The West Philippine Sea Basin (WPB), which is the main tectonic element of the Philippine Sea plate, includes the main basin, the northwest sub-basin and the southern sub-basin.Due to the complicated geological background and the geophysical features of the WPB,more and more geoscientists interest in this study area. Though studies of the WPB last a long time, even there are some researches on the movement evolution, there is still not a consistent conclusion of the oceanic crust age and the opening history of the WPB.Analysis on the present tectonic features with latest geophysical data and research on revising the oceanic crust age and the its movement evolution are full of significance for knowing more about evolution of the whole Philippine Sea Plate and its adjacent plates.Based on the previous research findings, the tectonic units of the western Philippines Sea plate and its tectonic relationship with the surrounding Eurasian plate, the Pacific plate and the Indo Australian plate are briefly introduced. Considering the terrain,landform and geographical tectonics and geophysical characteristics of the western Philippines basin, using the latest high resolution ocean gravity field model and satellite magnetic anomaly data, the study area's regional oceanic crust density distribution and magnetic structure are derived by using the potential data 3D inversion in the spherical coordinate system. What's more, combined with the heat flow distribution feature, we study the oceanic crust age in three parts, the main basin, the southern sub-basin and the northwestern sub-basin. Meanwhile, the constraints about geological age, the spreading center and the spreading form are roughly supplied, which supplied reference for the age modelling and the motion history recurrence.With help of the remanent magnetization magnetic lineation distribution caused by the oceanic crust spreading and geomagnetic polarity reversal, and through the magnetic identification we can get the magnetic picks which can be used to revise the oceanic crust age distribution and supply the initial data source of confirming the basin seafloor's opening mechanism. In this study, the high precision magnetic anomaly lineation data from a variety of sources in the West Philippines Basin area is collected, integrated, and processed by digitized and attribution specified. Then the magnetic picks and the main basin's crust age distribution are obtained. And, by using a new high-resolution global ocean gravity model, the opening direction constrain for the West Philippine Sea Basin is derived by extracting the seafloor tectonic structure trench in this study. In addition, the motion and oceanic curst age information of small tectonic units including the Palau Basin and the Huatung Basin are derived after through comparing the filtered and RTP magnetic data with the geomagnetic polarity reversal models.Using the processed magnetic anomaly data of West Philippines Basin, the lithosphere structure trench, the constraints about geological age, the spreading center and the spreading form, and based on the Spherical Euler motion criterion for plate motion, and with help of the GPlates, the magnetic anomaly identification, magnetic picks and the oceanic crust age isochrones distribution are obtained. Then the two phase opening history of the West Philippine Sea Basin are reproduced primarily, the main basin opening as a NE-SW direction in the first stage and it changes to the second phase with nearly N-S opening. The opening direction change time is about 41Ma and the cease time is about 34.1 Ma according to this study. The spreading motion of small basin of the West Philippine Basin area is different with the main basin. However, according to the magnetic lineation identification result by comparison between the ship track magnetic data and the geomagnetic polarity reversal model, the modelling results shows that the oceanic crust age of the Palau Basin is about 32?41 Ma with a half spreading rate 3.7 cm/yr and both the geophysical feature and age information shows that Palau Basin is not a south limb of the main basin; the oceanic crust age of the Huatung Basin is about 33?39 Ma with a half spreading rate 2.8 cm/yr and the gravity and magnetic anomaly feature shows the Huatung Basin is a part of the main basin because that it's lithosphere density and magnetic structure have good consecutiveness with the main basin's.