Self-organization of mid-ocean ridge segments during oblique oceanisation

Obliquely rifted continental margins are common, yet oblique spreading ridge segments are surprisingly rare. Oblique oceanisation, as seen in the southeast Indian Ocean, the Central Gulf of Aden, and the Equatorial Atlantic, invariably evolved into orthogonal ridge segments connected by transform faults. It remains unclear why the orthogonal ridge-transform configuration is preferred, and how it develops under sustained oblique divergence. Using 3D thermomechanical numeric models, we show that slow/ultraslow oblique spreading inherited from oblique rifting is a dynamic process. It enhances asymmetric oceanic plate growth with alternating directions and spontaneously self-organizes into orthogonal ridge segments connected with transform faults. The offset and spacing of the oceanic transform faults are controlled by the obliquity angle and the spreading rate. The step-wise orthogonal ridge-transform pattern is favored because it minimizes the total length of stronger ridge segments relative to weaker transforms, thereby reducing the mechanical work required for plate separation. Oblique spreading at slow to ultraslow rates fosters asymmetric growth of the ocean floor and leads to spontaneous formation of orthogonal ridge segments and new transform faults, according to thermomechanical simulations.