“Magmatism Controls Global Oceanic Transform Fault Topography”

Speaker: Dr. Xiaochuan Tian, Postdoctoral Research Fellow, Boston College

Abstract

Oceanic transform faults are fundamental features of plate tectonics, accommodating strike-slip motion between two adjacent mid-ocean ridge segments. The continuations of these faults form tectonically inactive fracture zones, creating the longest ‘scars’ on the Earth’s surface. Yet, despite the relatively simple kinematic and thermal structures, oceanic transform faults 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 local compression that generates fault-parallel ridges. The models not only reproduce the observed global transform valley depths but also predict the observation that fracture zones are consistently shallower than their adjacent transform valleys. These results suggest that plate motion changes are not a necessary condition for generating oceanic transform topography and that oceanic transform faults are not simple conservative strike-slip plate boundaries.