Continental slivers in oceanic transform faults controlled by tectonic inheritance

Abstract

The ocean floor shows variable morphological features, transtensional and transpressional structures, magmatic and amagmatic domains. Surprisingly, continental blocks separated from the continental margins from 100s or 1000s km distance have been occasionally reported, however, their origin remains debated. We conducted 3D magmatic-thermo-mechanical numerical experiments with the code I3ELVIS to simulate the dynamics of continental rifting, continental proto-transform fault zones, and eventually the formation of persistent oceanic transform faults and their connection to mantle melting. Numerical modelling results allow to analyze the first order features of passive and transform margins and oceanic basins. Our models explain the evolution of continental blocks entrapped between oceanic spreading ridges bounded by strike-slip fault zones inherited from the preceding continental rifting stage. The formation of such continental slivers is controlled by the relative timing between the onset of oceanic spreading and strain localization along strike-slip fault zones. This is connected to the rheology of the plates and also linked to different thermal gradients, divergence velocities, melting conditions and surface processes. Furthermore, we discuss the formation of zero-offset V-shaped oceanic fracture zones and the along-ridge variation of oceanic crustal thicknesses. Our model results are compared with observational data from the Romanche transform of the Equatorial Atlantic, the East Greenland Ridge and Newfoundland Ridge in the northern Atlantic, the Zabargad Islands in the Red Sea and the Davie Fracture Zone.