Stress-controlled magma-plumbing system during rift evolution

Rift zones host highly dynamic melt pathways in which magma may ascend vertically as dikes or migrate laterally to form sills, generating complex trans-crustal magma plumbing systems. While diking is a well-recognized consequence of extension, the mechanisms that promote sill emplacement during rifting remain poorly constrained. Here, we conduct high-resolution geodynamic models using ASPECT coupled with the surface process modeling code FastScape, to track the evolving lithospheric stress state over millions of years and assess its control on melt migration.Inspired by the Main Ethiopian Rift, the reference model comprises 40 km-thick crust of intermediate strength, featuring a 25 km-thick wet quartzite upper crust and a 15 km-thick wet anorthite lower crust, and is extended at a rate of 6 mm/yr. The model spans 12 Myr and accommodates 72 km of extension. Despite the overall extensional regime, the results reveal the development of localized compressional stress. This horizontal compression arises from flexure of the mechanically competent lithosphere during rifting and is concentrated at depths of 15–20 km and 5 km. In contrast, in weak crustal configurations, compression is confined to shallower levels (