Progressive Dissolution of Titanomagnetite in High‐Temperature Hydrothermal Vents Dramatically Reduces Magnetization of Basaltic Ocean Crust

Abstract

Abstract Hydrothermal alteration at high‐temperature vents near mid‐ocean ridge is thought to produce pervasive magnetization lows on basaltic ocean crust, but the detailed alteration process is insufficiently documented. Here, we performed microscopic and magnetic analyses on a large set of hydrothermal‐related basaltic samples from the Southwest Indian Ridge. Fresh basalts were chloritized and brecciated during hydrothermal alteration, where titanomagnetite nanoparticle clusters hosted in interstitial glasses were dissolved in the first order, followed by large micron‐scale dendritic particles. Natural remanent magnetization was reduced from 10 0 –10 1 A/m for fresh basalts to 10 −3 A/m for fully altered basalts. Hydrothermal deposits acquired a chemical remanent magnetization of 10 −2 A/m. Our results link direct magneto‐mineralogical observations to geophysical interpretations, which is important in understanding seafloor hydrothermal circulation and mid‐ocean ridge geodynamics.