Magmatism at Thick–Thin Lithosphere Transitions: Mantle Flow and Melt Generation from Numerical Modelling

An increasing number of studies identify craton boundaries marked by the transitions from thick to thin lithosphere as favorable regions for magmatism-derived mineralization. Similarly, numerous Cenozoic intraplate volcanic provinces are clustered or aligned with thick-to-thin lithosphere transitions, as observed in the Circum-Mediterranean region.

Proposed explanations for the origin of this magmatism invoke mantle flow patterns modulated by lithospheric steps or lithosphere-asthenosphere boundary (LAB) topography. These steps have been proposed to trigger edge-driven convection patterns potentially leading to decompression melting. Other hypotheses suggest that asthenospheric flow guided by LAB topography and directed toward adjacent thinner lithosphere produces decompression melting. However, recent studies suggest that these mechanisms are inefficient in generating long-lived high-volume magmatism.

This presentation explores convection patterns associated with thick-to-thin lithosphere transitions and investigates how they are modulated by asthenospheric thermal anomalies and/or extensional boundary conditions. We use numerical two-dimensional thermo-mechanical modelling to explore combined scenarios including variable buoyancy of the continental root, upwelling of mantle plumes, and distributed asthenospheric heating. The impact of each setting on mantle flow and melt production is assessed using the ASPECT open-source code, which employs a visco-plastic formulation. Preliminary results indicate that anomalous asthenospheric heating, likely associated with secondary mantle plumes, strongly enhances magmatism near the transition to thick lithosphere.