The Role of Viscous Coupling in Determining Subduction Style within Numerical Models of Mantle Convection
Abstract
Earth recycles its lithosphere through convective single-sided subduction, while other bodies, such as Mercury and Mars, exhibit stagnant lithospheres. Using a numerical model of mantle convection, StagYY, we investigate how this spectrum of behavior from 1-sided, to 2-sided, to stagnant lid may arise due to a combination of viscous coupling in the system. A 2D reference model includes a 80 km plate with maximum viscosity 1E25 Pa-s and 8 km of "weak crust", a viscous 1E20 Pa-s 660 km upper mantle of 1600 K, and 5E21 Pa-s 600 km lower mantle. The internal heated Rayleigh number remains constant at 1.8E8. The boundary conditions are free slip everywhere and the top has a pseudo-free surface with 100 km of sticky air. The weak crust has a lower viscosity than the mantle with values ranging between 0.001 and 1 times the mantle viscosity. The weak crust has different yield parameters than the mantle with values of cohesion ranging between 1 and 80 MPa (mantle value 150 MPa) and no depth dependence (mantle value 0.1). The weak crust converts back into mantle at a specified depth which is taken to be 150 km. Conversion depths less than 150 km result in stagnant lids due to a greatly increased viscous coupling at the plate interface. Similarly, this viscous coupling is sensitive to the minimum viscosity allowed (varied between 1E18 and 1E19 Pa-s). The system is more sensitive to crustal cohesion than the viscosity contrast which can alter the subduction style. These parameters control the amount of viscous coupling between the plate interface and within the mantle wedge. Within the parameter space, a window of 1-sided subduction appears for intermediate values of cohesion and viscosity contrast. Low values of cohesion lead to 2-sided subduction and high values lead to stagnant lid. In general, this is a nonlinear system due to the feedback between the stresses generated by viscous coupling and the amount of yielding in the weak crust both on the upper plate and atop the subducting plate.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.T31F2976J
- Keywords:
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- 1031 Subduction zone processes;
- GEOCHEMISTRYDE: 7240 Subduction zones;
- SEISMOLOGYDE: 8104 Continental margins: convergent;
- TECTONOPHYSICSDE: 8413 Subduction zone processes;
- VOLCANOLOGY