Magma transfer and pluton growth: Modelling short- and long-term processes by thermo-mechanical two-phase flow including the heat pipe mechanism

This study investigates the conditions sustaining long-lived molten plutons in the middle to upper crust, driven by lower crustal melting due to magmatic underplating and episodic melt extraction. Using 2D two-phase flow models solving conservation equations for mass, composition, momentum, and energy, and assuming a simplified melting law, we examine the interplay between long-term magmatic processes (e.g., lower crust heating, melt generation, segregation, diapiric ascent) and short-term dynamics (e.g., magma extraction, dyke ascent, emplacement). A novel melt extraction and intrusion formulation is introduced, varying parameters such as melt extraction volume threshold, intrusion depth, size, and geometry. Results indicate that smaller extraction thresholds lead to more frequent intrusions, increasing total melt volume in the intrusion and prolonging pluton lifespan. Intrusion geometry strongly influences melt accumulation: small radii (~2 km) favor significant melt volumes, while larger zones (>4 km) promote rapid freezing. Circular intrusions retain heat longer than dyke- or sill-like intrusions. Frequent intrusions promote vertical stacking of melt batches, pluton floor subsidence, and compositional stratification. Model-derived magma supply rates (0.15–0.3 km 3 /yr per extraction pulse; 0.001–0.002 km 3 /yr averaged over the total time extraction events) align with observed Central Andean magmatic systems. Melt extraction accelerates heat transport, producing early heat flux peaks (0.5–2 Myr) via the heat pipe mechanism, introduced in geoscience literature as a rapid transport of heat and mass through the lithosphere. This effect, quantified by a Nusselt number, increases with greater extracted melt volumes and shallower intrusions. Comparison with Central Andean heat flux data suggests a heat pipe Nusselt number of ~3.5, indicating extraction and intrusion enhance heat transport by this factor. These findings provide insights into the interplay between magmatism, heat transfer, and pluton evolution in continental crust. • We propose a new formulation for melt extraction and shallow intrusion for magmatic systems. • Rapid magma extraction increases surface heat flux by effective heat transport (heat pipe). • Multiple mama pulses lead to SiO 2 -rich intrusions with internal chemical layering. • Episodic magma extraction pulses may occur on time-scales of order of 100 kyrs. • Convection in the lower crust may occur or not depending on magma extraction efficiency.