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

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 degrees 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 thermomechanical 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 degrees 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 degrees 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 similar to 54 degrees C km(-1) at depth below where 700 degrees C occurs at the ridge axis. The models have little sensitivity to the wet or dry olivine rheology.& para;& para;Estimated viscosity is similar to 1 x 10(19) Pa s at 20-km depth at the ridge axis and similar to 1 x 10(18) 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 degrees 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. (C) 2017 Elsevier B.V. All rights reserved.