Research On Isostatic Gravity Anomaly Of The China South Sea

Isostatic gravity anomaly is one of the varieties gravity anomalies, which is obtained after the values of air correction, the middle layer correction and the topographic correction subtracted from the observed gravity. Geophysicists and geologists usually associate it with free air anomaly, bouguer anomaly together, to study the density distribution of the deep crust, geological structure and the delineation of abnormal body. The calculation and physical model of the free air anomaly and bouguer anomaly is simple and single, there is no dispute. Isostatic gravity anomaly is different, it depends on the isostatic model. Using different isostatic models lead to different results, so it is necessary to conside not only the sizes, shape, direction and other characteristics, but also the circumstance of the isostatic model when using the isostatic gravity anomaly to study the crustal structure and the isostasy of crustal.Geophysicists made a total of four isostatic models from introduction of the concept of isostasy up to now, there are Pratt isostatic model, Airy isostatic model, regional isostatic model and testing isostatic model. Both advantages and disadvantages of various models, but Pratt model and Airy model are commonly used model. This anomaly calculated by the South China Sea is a Airy isostatic model.South China Sea is located in Eurasia, the Pacific and Indian Ocean the junction of three plates, belonging to transitional crust tectonic domain between oceanic and continental crust tectonic domain. This tectonic complex, large-scale horizontal movement, large-scale horizontal movement along with the large-scale vertical motion, accompanied by a strong margin expansion in the strong marginsqueeze; Continental crust discreted in the northern margin, but also collaged in the southern margin; New oceanic crust born in the central basin, but disappeared in the east of the Manila trench; Epicontinental graben system formed during the continental margin expansion, island arc-trench system fault-fold growth in the extrusion process. Here, almost all types of tectonic movement, sedimentation, magmatism, metamorphism and mineralization has it's certain occurrence, development and evolution. Therefore, the studying on complicated geological structure and varied geological phenomenon have great theoretical and practical significance, to continental plates on the in-depth study of the interaction with the oceanic plate, the continental geology and marine geology of the contrast, explore oceanic crustand continental crust formation and metallogenic evolution of the law to understand the structure of the lithosphere composition further studying the East Asian continental margin and the global structure.This paper summarizes the calculation of gravity anomalies, and chose the isostatic model for the China South Sea. Secondly, the crustal-scale and the lithospheric-scale isostatic gravity are calculated, combined with existing geological and seismic data comparison, the lithospheric-scale isostatic gravity model is more consistent to adjust the isostasy of the China South Sea. Finally, the free air anomaly, the bouguer anomaly, the isostatic anomaly conducted a preliminary geological interpretation.