Variations in faulting style of the Southwest Indian Ridge (46°–53.5°E): Implications for crustal accretion process at ultraslow-spreading ridges

Abstract The variations in faulting style at the Southwest Indian Ridge (SWIR) 46°–53.5°E segment, correspond to different patterns of crustal accretion under different magma supply in an ultraslow-spreading ridge. We use multi-beam and filtered bathymetry to identify the fault characteristics and measure the fraction of magmatic accretion M and axial valley depth D. Four styles of faulting, namely, mode-C, mode-E, one-side detachment, and flip-flop detachment faults, are identified in the study area. The heave of these four faulting styles tends to increase gradually, and these faults can be progressive evolve in order from symmetrical to asymmetrical spreading. The reducing M significantly affects the faulting styles from mode-C to mode-E faults by largening fault heave, resulting in a deeper D at mode-E faults. However, there was no significant difference in M and D from mode-E to one-side detachment faults with the increase of heave. We consider that more magma may preferentially intrude into the asthenosphere at one-side detachment faults. Moreover, the flip-flop detachment faults are developed at the amagmatic segments, constrained by the extreme low M, talc- serpentinization, and dense transform faults.