A Near-Seafloor Study Reveal a Smaller Low Magnetization Zone of a Basalt-Hosted Hydrothermal Field at East Pacific Rise

Rock types of basement determine the magnetic signature of hydrothermal fields. Low magnetization zone (LMZ) is commonly observed at the basalt-hosted hydrothermal fields due to the fluid-rock interaction destroying the magnetic minerals inside basalt. We here report a near-seafloor magnetic survey conducted by the Autonomous Underwater Vehicle (AUV) over a basalt-hosted hydrothermal field on the East Pacific Rise (EPR). Inversed magnetization and Reduced-To-the-Pole (RTP) magnetic anomaly both show negative reduced magnetic signature centered on the hydrothermal field, reflecting enhanced demagnetization alteration process. Meanwhile, we delineate the range of the LMZ and compare it with the previous high-resolution near-seafloor magnetic studies on the fast-spread EPR, slow-spread Mid-Atlantic Ridge, and ultra-slow-spread Southwest Indian Ridge and Mohns Ridge. The statistical result shows that the diameter of LMZ increases with the decreasing spreading rate, suggesting the stable tectonic environment and focused melt supply at slower spreading ridge favor the birth of larger hydrothermal field.