A mechanical perspective on magma trapping, storage and ascent in rift-related volcanic systems

Understanding magma pathways and eruptive vent patterns is fundamental to deciphering how volcanic systems evolve in regard to their surface and subsurface structure, magma chemistry, and eruptive style. Recent studies have emphasized the critical role of the crustal stress field in controlling magma ascent, including magma trapping and prolonged storage in crustal volumes defined by stress field patterns. In extensional tectonic regimes, the influence of stress on magma pathways and vent distributions has been explored mainly across and along rift axes, showing that unloading and extension tend to focus magma pathways toward rift shoulders or rift tips, producing either distributed or localized vent patterns. These patterns are sensitive to basin geometry and the relative magnitudes of unloading and tensional stresses.

In this contribution, I first illustrate how unloading associated with extensional basins modifies the crustal stress field and promotes magma trapping at specific depths. Using stress-based models of magma propagation, I show that basin-related unloading can, in spite of extension, inhibit vertical ascent and favor the formation of laterally extensive, sub-horizontal magma storage zones, where magmas, deprived of their buoyancy, are effectively trapped. This leads to prolonged magma residence prior to eruption, creating the opportunity for cooling and chemical exchange with the host rock and successive magma batches reaching the stress trap. Upon eventual ascent, stress conditions drive dikes to propagate obliquely and then vertically, accelerating magma transport; together with volatile exsolution, this promotes conditions favorable for explosive eruptions. These results provide a mechanical framework linking tectonic forces, magma pathways, magma evolution, eruptive style and caldera formation in rift-related volcanic systems.