Magmatism Controls Oceanic Transform Fault Topography

Abstract Oceanic transform faults are fundamental features of plate tectonics, accommodating strike-slip motion between two adjacent mid-ocean ridge spreading segments. The continuations of these faults form tectonically inactive fracture zones, creating the longest ‘scars’ on the Earth’s surface. However, despite the relatively simple kinematic, thermal, and compositional structures of oceanic transform faults and fracture zones, these features display an enigmatic continuum of morphologies ranging from deep valleys to small ridges. Here, through three-dimensional numerical modeling of two mid-ocean ridge segments separated by a transform fault, we find that the rate of magma intrusion within the transform domain exerts a first-order control on transform topography. Low-rate magmatism results in transform-parallel tectonic stretching, generating deep transform valleys and fracture zones. Intermediate-rate magmatism fully accommodates far-field stretching, but strike-slip motion induces across-transform tension, producing shallow valleys whose depth increases with the shear strength of the fault. High-rate magmatism leads to curved plate boundaries and local compression that generates fault-parallel ridges. Thus, the global spectrum of transform topography is controlled by spreading-rate dependent variations in magmatism and can arise without changes of plate motion.