Transform Faults or Overlapping Spreading Centers? Oceanic ridge interactions revealed by analogue models

Transform faults and Overlapping Spreading Centers (OSC) are the two most common types of interaction between oceanic ridge segments. Various factors have been proposed to control one interaction type or the other. However, measurements of several tens of transforms and OSC reveal that a simple ratio, between the total length of the interacting ridge segments (L) and their overstep (S), distinguishes transforms (L/S<6) from OSC (L/S>11). Scaled experiments have been performed to test the possibility that the initial configuration of neighbor ridges controls the interaction type. With L/S<5, experimental transforms develop, provided that minor ridge-parallel extension (~14% of ridge-perpendicular extension at the moment of formation of the transform structure) is present; without ridge-parallel extension, experimental OSC form instead of transforms. With L/S>12, OSC always develop at earlier stages, independently from any ridge-parallel extension. Ridge-parallel extension, commonly observed along oceanic ridges, may accommodate the increase in length of an oceanic divergent boundary during its migration and expansion, enhancing the development of transforms under suitable L/S conditions. The matching between experimental and natural data suggests that the interaction type between oceanic ridges depends from their initial configuration and, subsequently, the overall growth of the divergent boundary.