Thermo-mechanical model of the mantle wedge in Central Mexican subduction zone and a blob tracing approach for the magma transport

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The origin of the Central Mexican Volcanic Belt (CMVB) and the influence of the subducting Cocos plate on the CMVB volcanism are still controversial. In this study, the temperature and mantle wedge flow models for the Mexican subduction zone are developed using the finite element method to investigate the thermal structure below CMVB. The numerical scheme solves a system of 2D Stokes equations and 2D steady-state heat transfer equation. Two models are considered for the mantle wedge: the first one with an isoviscous mantle wedge and the second one with strong temperature-dependent viscosity. The first model reveals a maximum temperature of ∼830 °C in the mantle wedge, which is not sufficient for melting of wet peridotite. Also, the geotherm of the subducting plate upper surface does not intersect the dehydration-melting solidus for mafic minerals. The second model predicts temperatures of more than 1200 °C beneath the CMVB for a wide range of rheological parameters (reference viscosity and activation energy). Up to 0.6 wt.% H 2O can be released down to 60 km depth through metamorphic changes in the oceanic crust of the subducting slab. The melting of this oceanic crust apparently occurs in a narrow depth range of 50–60 km and also melting of the mantle wedge hydrated peridotite is now expected to take place beneath CMVB. Considering that the melting processes on and in the vicinity of the subducting plate surface generate the most of the volcanic material, a dynamic model for the blob tracers is developed using Stokes flow at infinite Prandtl number. The blobs of 0.2–10.0 km in diameter migrate along very different trajectories only at low wrapping viscosities ( η w = 10 14–5 × 10 17 Pa s). The modeling results show that the “fast” trajectories terminate at the same focus location at the base of the continental crust, while the arrival points of “slow” trajectories, which are common for the blobs of smaller size (∼0.4–0.5 km), are scattered away from the average focus location. This observation may give us a hint on a possible mechanism of strato and mono volcanoes genesis. The rise time, which the blob detached from the subducted plate, needs to reach the bottom of the continental crust, is from 0.001 up to 14 million years depending on the blob diameter and surrounding viscosity.