Reactive Fluid Flow in Generation of Felsic Crust

Understanding the formation of continental crust, predominantly felsic and rich in silicon and aluminum, remains a key challenge in geoscience. Current models emphasize magmatic differentiation of basaltic magma, produced by partial melting of mantle peridotite induced by fluids from subducting oceanic crust.

However, over 70 years ago, D.S. Korzhinsky proposed the principle of alkali mobility during metamorphism and granitization, emphasizing the significance of alkali (K₂O, Na₂O) and volatile components (H₂O, CO₂) in crust formation [1]. His insights highlighted the role of transmagmatic fluids but lacked a physical framework for describing fluid transport through silicate melts.

Building on Korzhinsky’s concept, we propose a coupled mathematical model that describes the migration of multi-component aqueous solutions at the lithosphere’s base, driven by (de)compaction of fluid-saturated viscoelastic rocks and accompanied by (de)hydration reactions. This model incorporates fluid-rock interactions within vein structures and accounts for changes in density and composition of coexisting phases. Thermodynamic calculations using THERMOLAB [3] reveal that SiO₂ content in fluids significantly influences mineral assemblages. For example, decompression from 2.5 to 0.2 GPa at 700°C transitions a six-mineral system to a three-phase assemblage, increasing the Si/O ratio and priming the mantle protolith for felsic melt generation.

This approach, validated through numerical simulations [4], advances the understanding of metasomatic processes, offering a robust framework to explore fluid-mediated mechanisms in continental crust formation.

 

[1] Korzhinskii, D. S. Transmagmatic Fluid Flows of Subcrustal Origin and Their Role in Magmatism and Metamorphism. Crust and Upper Mantle of the Earth (IGC, XXIII Session. Reports of Soviet Geologists, Problem 1), Moscow: Nauka, 1968, pp. 69-74.

[2] Aranovich, L. Y. The Role of Brines in High-Temperature Metamorphism and Granitization. Petrology, 2017, Vol. 25, No. 5, pp. 491-503.

[3] Vrijmoed, J. C., & Podladchikov, Y. Y. Thermolab: A Thermodynamics Laboratory for Nonlinear Transport Processes in Open Systems. Geochemistry, Geophysics, Geosystems, 2022, Vol. 23, No. 4, e2021GC010303.

[4] Khakimova, L., & Podladchikov, Y. Modeling Multicomponent Fluid Flow in Deforming and Reacting Porous Rock. Petrology, 2024, Vol. 32, No. 1, pp. 2-15.