Magmatism at oceanic core complexes on the ultraslow Southwest Indian Ridge: Insights from near-seafloor magnetics

Abstract

Oceanic core complexes (OCCs) and detachment faults play a key role in crustal accretion at slow and ultraslow spreading centers. We investigated the effect of different magma supply at three OCCs of the Southwest Indian Ridge using high-resolution deep-sea bathymetric and magnetic data. The average equivalent thickness of extrusive basalt deduced from the magnetic anomalies, a proxy for magma supply, decreases from west to east, from the Yuhuang (49.25°E) to Longqi (49.65°E) to Junhui (51.75°E) OCCs. Conversely, serpentinite outcrops become more abundant, the domal OCC morphology flattens as the footwall rotation (measured by the magnetization vector inclination) increases, and hydrothermal evidence becomes sparse. Combined with results from the amagmatic easternmost Southwest Indian Ridge, our study shows that the magma supply controls the character and evolution of the OCCs and detachment faults on the Southwest Indian Ridge.

Coupled Detachment Faulting and Hydrothermal Circulation at 49.7°E Southwest Indian Ridge Revealed by Seafloor Magnetism

“…However, more active hydrothermal vents were found in the M zone than in the S zone (Figures 1c and 8d), and it was inferred that the alteration zone underneath the Longqi hydrothermal field migrated northward (Wu et al., 2021). Overall, the Longqi hydrothermal field is located at the termination of the detachment fault in the Dragon Horn area (Figure 1b; Zhao et al., 2013; Zhou et al., 2022); thus, the hydrothermal channel orientation is controlled by multiple fracture activities. The estimated chloritized basalt unit in the Longqi hydrothermal field extends approximately 100 m below the seafloor (Figures 7d–7f, 8d and 8e), which is close to TAG (Galley et al., 2021) and Suye hydrothermal fields.…”

“…The occurrence of hydrothermal circulation along mid‐ocean ridges is considered to increase linearly with spreading rate (Baker et al., 1996), but intensive surveys have revealed that hydrothermal circulation in slow‐ and ultraslow‐spreading mid‐ocean ridges may be underestimated (Baker, 2017; Baker et al., 2016). Detachment faults are essential for hydrothermal circulation at slow‐ and ultraslow‐spreading mid‐ocean ridges (e.g., DeMartin et al., 2007; Zhou et al., 2022) because their deep penetration can provide pathways for fluid and heat migration (Tao et al., 2020). In addition, footwall rotation exposes the lower crust on the seafloor (Garcés & Gee, 2007; Morris et al., 2009), promoting reactions between hydrothermal fluids and oceanic crust.…”

Sensitivity of mid-ocean ridge hydrothermal system controlled by the detachment fault to the glacial cycle

“…This holds regardless of the heat source, hydrothermal circulation depth and uid composition, hydrothermal activity life, stability over time, etc. 13,14,16,17 . Therefore, the response of hydrothermal activity to the glacial cycle would also be different between hydrothermal systems with different types and spreading rates of the host ridge segments.…”

“…1b). Recent studies have revealed that the Yuhuang HF is located on the hanging wall of a detachment fault, and thus controlled by tectonic activity and affected by magmatic activity, and its sul de formation is multi-stage 17,20 . The presence of a large detachment fault in this area, as well as hot anomalous magma, maintains long-term hydrothermal activity in the Yuhuang HF, forming a large (and rare) accumulation of 45.1 Mt of sea oor massive sul des 11,17,19 .…”

The effect of brittle-ductile weakening on the formation of tectonic patterns at mid-ocean ridges

“…In contrast to the symmetric and high-angle normal faults in fast-spreading centers, slow-spreading ridges are characterized by asymmetric, large-offset, and low-angle detachment faults with oceanic core complexes (MacLeod et al, 2011;Sauter et al, 2013). Previous studies suggested that the crucial factor in the seafloor tectonic patterns may be the ratio of magmatically accommodated extension to total plate separation which is mainly controlled by spreading rates (Buck et al, 2005;Olive and Dublanchet, 2020;Liu et al, 2022;Zhou et al, 2022). Low magma supply and thick axial lithosphere in slow-spreading ridges facilitate the formation of detachment faults, while normal faults in axial topographic high spreading centers are very sensitive to fast-spreading rate and thin axial lithosphere with full magma supply.…”