25-9 Thermodynamic Modeling of Subduction-Mélange and Hydrated Lithospheric Mantle Constrains Water Fluxes, Seismicity, and Arc Magmatism Along the Cocos Plate Beneath Central Mexico

Session: Integrating metamorphism, mass transfer, and magmatism across the American Cordillera (Posters)

Poster Booth No.: 53

Presenting Author:

Fabián Gutiérrez Aguilar

Authors:

Gutiérrez Aguilar, Fabián¹, Parolari, Mattia², Gómez Tuena, Arturo³, Hernández Uribe, David⁴, Ramírez Salazar, Anthony⁵

Abstract:

Beneath central Mexico, the Cocos plate exhibits flat-to-steep subduction, driving fluid-related processes like slow slip events (SSE) and intermediate-depth seismicity (IDS) to mantle serpentinization and H₂O -rich magmatism in the Trans-Mexican Volcanic Belt (TMVB). Yet, the controls on how and where these fluids are generated and transferred—whether governed by slab dehydration, redox conditions, or lithologic heterogeneity—remain debated. In this work, we apply Gibbs free-energy minimization along slab-top and Moho geotherms to model phase equilibria, H₂O release, porosity, volume change, and fluid flux in sediments, mafic oceanic crust, hydrated lithospheric mantle, and subduction-mélange under varying hydration, redox, and hybridization. Sediments and mafic crust dehydrate at shallow to intermediate depths, limiting deep fluid transport. Instead, along the flat slab, talc- and chlorite-rich subduction-mélanges and serpentinized mantle retain most bound water, keeping porosity <0.01 and trapping fluids in an overpressured interface consistent with SSE. As the slab steepens, epidote breakdown in subduction-mélanges and brucite + amphibole + antigorite breakdown in serpentinized mantle generate dehydration pulses up to ~10⁷ kg m^–2 Myr^–1, porosity up to 0.5, and solid + fluid volume changes ≤355.7 J bar⁻¹, exceeding percolation thresholds and promoting IDS by dehydration embrittlement and stress transfer. During steep subduction, amphibole (subduction-mélange) and antigorite + chlorite (lithospheric mantle) breakdown deliver a 10⁹ Tg H₂O Myr^–1 flux to the mantle wedge, fueling TMVB magmas. Thus, subduction-mélanges and hydrated lithospheric mantle form a connected fluid system that mediates where fluids accumulate, when they are released, and how they modulate the Cocos plate’s mechanical behavior.

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