Study On Data Processing And Interpretation Methods Of Near-seafloor Magnetic Data And Its Application At The Yuhuang Hydrothermal Area

Hydrothermal area located in the oceanic ridges is one of the most important discoveries in the 20 th century.It has been being a hotspot filed for studying inner process of the Earth and exploration of sulfide minerals.Hydrothermal areas usually have particular physical and chemistry process,making their rocks gain different properties and physical characters from normal ocean crust,which in turn to produce magnetic anomaly over these areas.Given these reasons,we can use magnetic methods to study hydrothermal areas.Comparing to the traditional ship-loaded magnetic exploration,near-seafloor magnetic method has higher resolution,making it has priority of studying hydrothermal areas' structure and finding the potential areas.However,because of the short-time development of this technique,its data processing and inversion methods of magnetic data is needed to be improved.In addition,its application in the practical hydrothermal areas,especially the typical hydrothermal areas in china's contract area at the South-West Indian Ridge,is little and magnetic structure and evolution history of these areas have not been clear.Therefore,improving the data processing and inversion methods and applying the methods in the typical hydrothermal areas at the South-West Indian ridge are the urgent problem to solve.Our study focus on the near-bottom magnetic data of china's 4500 m Autonomous Underwater Vehicle,“Qianlong II”.To begin with,we introduced adaptive filter method and interpolation-iteration continuation method to filter out the random noise and error introduced by the altitude variation of AUV,respectively,arising the precise of data.In addition,using 3D forward method based on the cubic discretion and 3D focused inversion method to obtain the magnetization model and introducing terrain weighting to inverse the precise magnetization structure of the hydrothermal areas with complicate terrain.Model experiment and processing of practical data both prove the effectiveness of the mentioned methods.Given above method system,we processed and interpreted actual near-bottom magnetic data over Yuhuang hydrothermal area at the South-West Indian Ridge.After obtaining the inversed 3D magnetization structure of the study area,we connected the samples distribution gotten from the previous cruise and rock's physical characters to give a synthetic interpretation of our inversion result.We thought that the known Yuhuang I site is a basalt-hosted site and its low magnetization is aroused by the low magnetic sulfide deposit and demagnetization process of basalt's alteration,whereas Yuhuang II is probably an ultramafic-hosted site whose high magnetization comes from the magnetite produced in the serpentinization process.Finally,we concluded that Yuhuang hydrothermal area is controlled by detachment fault and basalt-hosted hydrothermal site and ultramafic-hosted hydrothermal site both exist,which subsequently helps us summarize two situations that two kinds of sites exist in a detachment-fault controlled hydrothermal system.