244-2 Numerical Model of Slip Behavior, Fluid Flow, and Pressure Solution along the Subduction Plate Interface

Session: Subduction Zone Processes: Insights from Geology, Geochemistry, and Petrochronology

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Abstract:

We incorporate a pressure solution flow law (combined with a dislocation creep flow law for quartz-phyllosilicate mixtures) into a numerical model that depicts interseismic creep, seismicity, and fluid flow, including the fluid flow transients that occur during earthquakes. This model (MEFISTO- a Mineralization, Earthquake, and Fluid flow Integrated SimulatOr) includes:1) an earthquake simulator with temperature-dependent increases in cohesion, 2) a fluid flow model coupled to the earthquake simulator through the link between increasing strength (contact area) and permeability, with both low strength and ambient permeability restored by ruptures of the plate interface, and 3) interseismic creep that responds to variations in stress that could drive acceleration in strain rate toward the later part of the seismic cycle.  The fluid moves down a pressure gradient driven by fluid production from metamorphic reactions within and downdip of the seismogenic zone.  An increase in average shear stress with increasing lithostatic stress along the interface emerges during simulations, with a very low effective coefficient of friction (~0.07), consistent with the shear stress estimates based on heat flow in the forearc.  Pressure solution, which is capable of producing measurable strain in mudstones at the updip end of the seismogenic zone (100-150˚C), increases downdip to a point along the interface where the strain rate is capable of accommodating the plate rate.  Silica saturation state is tracked using an expression for the P-T dependence of equilibrium solubility that is based on experiments and included in the flow law. Silica precipitates in response to fluid advection, both during ambient fluid flow and transients with systematic precipitation relative to earthquake ruptures. No reasonable values for permeability lead to precipitation rates from advecting fluid capable of explaining the volumes of vein quartz in rocks exhumed from the interface. Strain measurements for dissolution along the scaly fabric indicate that local dissolution-precipitation creep is capable of producing the observed vein density, so pressure solution is likely the primary mechanism for increasing cohesion, or healing of the plate interface in the aftermath of earthquakes in subduction zones. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8742

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