How does the initial configuration of oceanic ridge segments affect their interaction? Insights from analogue models

Oceanic ridge segments interact forming different types of structures, of which transform faults and overlapping spreading centers represent the most common end-members. This study uses analogue models for testing the role of the initial configuration of the ridges on the geometry and kinematics of the resulting interaction zones. The models, run in a centrifuge, consist of a lighter silicone (LDS), rising within a denser silicone (HDS) below a brittle layer simulating the oceanic lithosphere. Pre-cut fractures in the brittle layer simulate the initial configuration of oceanic ridges. The rise and lateral spreading of the LDS induce the propagation, widening, interaction and linkage of the fractures. We varied the offset and overlap between the fractures, obtaining 10 distinctive types of interaction. Variations in fracture overlap and offset define several interaction types. Increase of fracture overlap leads to interaction zones of lower aspect ratio, with fractures propagating at lower angles to the mean extension direction. Increase of offset leads to the elongation of the interaction zones with the new fractures propagating subparallel to the extension direction. The comparison with several examples of natural ridges shows close geometric similarities, confirming the existence of predominant types of ridge interaction. Among these, ridges with smaller offsets develop interactions similar to overlapping spreading centers, whereas ridges with larger offsets have geometries reminiscent of transform zones. The comparison between experimental and natural examples suggests that the observed wide spectrum of ridge interaction types in nature results from the initial configuration of the divergent plate boundary.