Rheological responses to plate boundary deformation at the Eastern Volcanic Zone in Iceland

- A new geodynamic finite element model (FEM) for divergent plate boundary deformation is provided.
- Geodynamic FEM model considers temperature- and stress-dependent viscoelastic olivine rheology.
- Detailed sub-surface temperature is reproduced.
- In the FEM model, 700 °C demarcates the layer where elastic deformation is the greatest.

Located on the mid-Atlantic ridge, Iceland allows for direct measurement of crustal deformation. Global Positioning System (GPS) data from the Eastern Volcanic Zone (EVZ), Iceland, and crustal deformation of the rift near its southern end at 64°N show a spreading rate of 13.8 ± 1.8 mm yr− 1. About 90% of the deformation occurs in an 80 to 90-km wide zone. To understand how the rheology of the lithosphere influences rifting, we applied a thermo-mechanical stretching model that includes thermal states in Iceland using temperature- and stress-dependent wet and dry olivine rheology. We attempt to reproduce the thermal structure of a rift by defining 700 °C from 5- to 15-km depth at the rift axis that leads to variation in rheological structure, and to estimate the layer (from surface to a depth of 700 °C) where the elastic deformation of the lithosphere is the greatest. At a fixed spreading rate, the deformation field is controlled by the sub-surface thermal state. The vertical subsidence rate at the ridge axis increases almost linearly as the half-velocity increases. The best fitted model suggests a thermal gradient of ~ 54 °C km− 1 at depth below where 700 °C occurs at the ridge axis. The models have little sensitivity to the wet or dry olivine rheology.Estimated viscosity is ~ 1 × 1019 Pa s at 20-km depth at the ridge axis and ~ 1 × 1018 Pa s up to 100-km depth in the model. The spreading rate influences the tangential (non-linearity) shape of the deformation field, and a change in spreading rate affects the deformation field the most. After spreading velocity, the model's second most sensitive parameter is the location of the 700 °C at the rift axis. The thermomechanical model confirms that the rheological responses at the central part of the rift zone in the EVZ, Iceland caused of plate spreading is nonlinear, comparable with surface deformation observed by GPS measurement.