Syn‐Rift Magmatism and Oceanic Spreading Initiation Controlled by Rift Obliquity: Insights From 3D Coupled Thermo‐Mechanical and Surface Processes Modeling

Abstract Continental rifting is often oblique, controlled by various inherited weak crustal and mantle heterogeneities striking at non‐orthogonal angles to the direction of extension. Oblique rifting is known to induce strain partitioning and along‐strike segmentation of the rift structure, but its effects on the magma generation and spreading initiation have remained insufficiently explored. In this study, we used coupled 3D petrological–thermo‐mechanical and surface processes numerical models to quantify the dynamic feedbacks between rift obliquity, crustal faulting, thermal evolution, magmatism, and erosion and sedimentation processes. The models show that increasing rift obliquity delays the onset of melting and non‐linearly reduces the crustal melt supply, whereas the mantle melt volumes are much less influenced. Spatial distribution of the crustal melting zones follows the same segmented en echelon arrangement as the main fault zones, suggesting a strong structural control over the crustal melt generation. Subsequently, the location of the first continental break‐up is linked to the thermally most weakened sub‐orthogonal rift segments, followed by along‐strike propagation of the offset spreading centers. The rate of this propagation changes in space and time, driven by the variable efficiency of strain localization. The models also suggest that above 30° rift obliquity, deformation between the offset spreading centers may be accommodated by oceanic transform faults, which form spontaneously during the late stage of spreading initiation. These model predictions are in good agreement with observations from the Woodlark Basin and Main Ethiopian Rift.