| Antarctic and its adjacent sea area is becoming an important region, because there are rich resources and an ideal place for studying environmental change. By carrying out marine geophysical survey and evaluation and detecting the stratigraphic distribution characteristics beneath Antarctic continental shelf, one could obtain some important information environmental changes which have been recorded by the stratigraphy. As a basic method of marine geophysical investigation, marine gravimetric survey is of important significance for studying the geological and tectonic characteristics and regional tectonic evolution in the Antarctic area, and further investigating Antarctic sea area resource and performing global change studies.In 1984, China carried out the first marine gravity survey for Antarctic Peninsula and Bransfield Strait. Since then, China has carried out 31 Antarctic expeditions, obtained a large amount of data for the Bransfield Strait and Prydz Bay. However, some factors such as sea ice, wave, positioning accuracy and other factors, as well as the skimble-scamble instruments and other issues, result in relatively large accidental errors and systematic errors in final results.Based on the measured data in the Antarctic Peninsula and Bransfield Strait,combined with the international public data, this study adopts a series methods including precision control, least-square adjustment method, fusion of ship-derived gravity data, gravity field and structure analysis to analyze the data, and eventually summarized a set of methods which is suitable for gravity data processing of polar sea area. The results showed that by using point-by-point analysis, least squares filtering,analyzing of cross-coupling correction and recalibration of e?tv?s effect correction in sequence, one can reach the requirement of controlling the accuracy in the data processing.This study took use of the measured data for the study area to analyze theregional gravitational field, and inverted the Moho depth of based on airy isostatic model, and calculated the gravity anomalies based on isostatic correction. The results obtained above, combined with collected seismic data, have been used to indicate regional gravitational field and tectonic features. The main conclusions are as follows,(1)The free-air gravity anomaly was separated by NNW-trending tectonic lines and submarine volcanoes, and there also formed multiple abnormal low traps in the central trough.(2)The Bouguer gravity anomaly in the strait rose up from both sides to the middle, and the slope break with a value of 100×10-5m/s2 can be regarded as a line dividing high value region and low value region. Two traps with anomaly high values,with the highest value up to 150×10-5m/s2, appeared in the central trough and the seamounts in eastern trough, respectively. In addition, there formed multiple trap anomalies in continental slope area.(3)The continuity of Moho depth for areas among islands in study area was often cut off by later seafloor volcanic and tectonic activities, which is consistent with those shown by tectonic framework. The minimum value of Moho depth(12km) appeared in the back-arc spreading area. And, the depth gradually increased toward both sides(e.g., Bransfield Strait and Antarctic Peninsula) from the back-arc spreading area, and that for slope area was 24 km.(4) In general, the back-arc spreading center in the Bransfield Strait showed more isostatic than its adjacent areas. In the position of submarine volcanoes of Central Bransfield Basin, there showed the highest value in isostatic residual gravity anomaly, and the anomaly field was surrounded by the value of 60×10-5m/s2. |
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