High-resolution magnetic exploration of Longqi hydrothermal field (49.6°E) on SWIR

Studies in recent years have shown that high-resolution magnetic exploration of both low- and high-temperature hydrothermal vent fields found in basalt- and ultramafic-hosted areas is a crucial geophysical surveying method for locating and characterizing these sites. We have recently analyzed and inverted near-bottom magnetic field data collected by autonomous vehicles Qianlong II and ABE in the Longqi hydrothermal field (49.6°E) on the Southwest Indian Ridge (SWIR). The observed magnetic anomaly field data have undergone conventional processing that includes, data filtering, corrections for the interference caused by the AUV platform, and removal of Earth's geomagnetic reference field (IGRF). The magnetic anomaly data were then inverted to obtain a 3-D magnetization distribution using a 3-D focused inversion method. We chose focus areas with different grid mesh sizes to target the sulfide deposit and ocean core complex (OCC) region within the overall regional study area. The inversion results show that a strong magnetization zone, possibly a dike, is located below the north main mound and underneath the OCC region, and a reduced magnetization zone, a circle of radius 120 m, is found below the sulfide deposit, likely due to an altered rock body. Finally, we combine the geological survey data from the hydrothermal vent distribution mapped by the HOV Jiaolong and geological sampling by the TV-grab (TVG), to provide insight into the magnetic inversion results and discuss these in the context of the hydrothermal circulation present at this site.