Multi-stage detachment faulting controls hydrothermal activity in the Dragon Horn area (49.7°E, SWIR): Insight from magnetic studies

The existing and evolution of detachment fault plays an important role in hydrothermal circulation at ultramafic mid-ocean ridges where lack of enough magmatic supply. Near-bottom magnetic exploration considered as a crucial way for characterizing hydrothermal areas and detachment faults. Here, sea-surface and high-resolution near-bottom magnetic data and series rock samples were obtained on hydrothermal area in Dragon Horn, where developed detachment fault (DF) system, along ultra-slow southwest Indian ridge. Sea-surface magnetic results suggested that the DF system probably began before 0.48 Ma and detached about 4.1 km. Near-bottom magnetic results mapped the structure of DF system, revealed that the system undergone multi-stage detachment and left a slipped block on oceanic complex core (OCC) surface, which also can get support from the petrological properties of located rock samples and can be verified by magnetic forward modeling with 2-D geomagnetic models. Furthermore, we mapped the magnetic features of hydrothermal area where an obvious high magnetization dike presented in the main mound, and relatively low but without detail low magnetization obtained in the hydrothermal area as survey line spacing is too wide and the weak anomaly drowned out by lavas. Nonetheless, we discussed the evolutionary relationship between DF system and hydrothermal activity and believed that multi-stage DF system dominated hydrothermal activity in Dragon Horn. The research results can provide evidence for hydrothermal system evolution.